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James A, Coffeng LE, Blok DJ, King JD, de Vlas SJ, Stolk WA. Predictive Value of Microfilariae-Based Stop-MDA Thresholds After Triple Drug Therapy With IDA Against Lymphatic Filariasis in Treatment-Naive Indian Settings. Clin Infect Dis 2024; 78:S131-S137. [PMID: 38662696 PMCID: PMC11045019 DOI: 10.1093/cid/ciae019] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2024] Open
Abstract
Mass drug administration (MDA) of antifilarial drugs is the main strategy for the elimination of lymphatic filariasis (LF). Recent clinical trials indicated that the triple-drug therapy with ivermectin, diethylcarbamazine, and albendazole (IDA) is much more effective against LF than the widely used two-drug combinations (albendazole plus either ivermectin or diethylcarbamazine). For IDA-based MDA, the stop-MDA decision is made based on microfilariae (mf) prevalence in adults. In this study, we assess how the probability of eventually reaching elimination of transmission depends on the critical threshold used in transmission assessment surveys (TAS-es) to define whether transmission was successfully suppressed and triple-drug MDA can be stopped. This analysis focuses on treatment-naive Indian settings. We do this for a range of epidemiological and programmatic contexts, using the established LYMFASIM model for transmission and control of LF. Based on our simulations, a single TAS, one year after the last MDA round, provides limited predictive value of having achieved suppressed transmission, while a higher MDA coverage increases elimination probability, thus leading to a higher predictive value. Every additional TAS, conditional on previous TAS-es being passed with the same threshold, further improves the predictive value for low values of stop-MDA thresholds. An mf prevalence threshold of 0.5% corresponding to TAS-3 results in ≥95% predictive value even when the MDA coverage is relatively low.
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Affiliation(s)
- Ananthu James
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Luc E Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - David J Blok
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Jonathan D King
- Department of Control of Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Wilma A Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
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2
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Kura K, Mutono N, Basáñez MG, Collyer BS, Coffeng LE, Thumbi SM, Anderson RM. How Does Treatment Coverage and Proportion Never Treated Influence the Success of Schistosoma mansoni Elimination as a Public Health Problem by 2030? Clin Infect Dis 2024; 78:S126-S130. [PMID: 38662698 PMCID: PMC11045018 DOI: 10.1093/cid/ciae074] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2024] Open
Abstract
BACKGROUND The 2030 target for schistosomiasis is elimination as a public health problem (EPHP), achieved when the prevalence of heavy-intensity infection among school-aged children (SAC) reduces to <1%. To achieve this, the new World Health Organization guidelines recommend a broader target of population to include pre-SAC and adults. However, the probability of achieving EPHP should be expected to depend on patterns in repeated uptake of mass drug administration by individuals. METHODS We employed 2 individual-based stochastic models to evaluate the impact of school-based and community-wide treatment and calculated the number of rounds required to achieve EPHP for Schistosoma mansoni by considering various levels of the population never treated (NT). We also considered 2 age-intensity profiles, corresponding to a low and high burden of infection in adults. RESULTS The number of rounds needed to achieve this target depends on the baseline prevalence and the coverage used. For low- and moderate-transmission areas, EPHP can be achieved within 7 years if NT ≤10% and NT <5%, respectively. In high-transmission areas, community-wide treatment with NT <1% is required to achieve EPHP. CONCLUSIONS The higher the intensity of transmission, and the lower the treatment coverage, the lower the acceptable value of NT becomes. Using more efficacious treatment regimens would permit NT values to be marginally higher. A balance between target treatment coverage and NT values may be an adequate treatment strategy depending on the epidemiological setting, but striving to increase coverage and/or minimize NT can shorten program duration.
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Affiliation(s)
- Klodeta Kura
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London
- Medical Research Council Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, United Kingdom
| | - Nyamai Mutono
- Centre for Epidemiological Modelling and Analysis, University of Nairobi, Kenya
- Paul G. Allen School for Global Health, Washington State University, Pullman
| | - Maria-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London
- Medical Research Council Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, United Kingdom
| | - Benjamin S Collyer
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London
- Medical Research Council Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, United Kingdom
| | - Luc E Coffeng
- Department of Public Health, Erasmus University Medical Center, University Medical Center Rotterdam, The Netherlands
| | - S M Thumbi
- Centre for Epidemiological Modelling and Analysis, University of Nairobi, Kenya
- Paul G. Allen School for Global Health, Washington State University, Pullman
- Institute of Immunology and Infection Research, University of Edinburgh, United Kingdom
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London
- Medical Research Council Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, United Kingdom
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Collyer BS, Anderson R. The transmission dynamics of Strongyloides stercoralis and the impact of mass drug administration. Philos Trans R Soc Lond B Biol Sci 2024; 379:20220442. [PMID: 38008114 PMCID: PMC10676814 DOI: 10.1098/rstb.2022.0442] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2023] [Accepted: 10/30/2023] [Indexed: 11/28/2023] Open
Abstract
The epidemiology of Strongyloides stercoralis is briefly reviewed with an emphasis on cross section and longitudinal studies of infection prevalence stratified by age, performance of different diagnostic tools, mass drug administration (MDA) impact and estimates of key population parameters within the complex life cycle of the parasite that determine transmission intensity and response to control measures. The paucity of studies is highlighted, and gaps in current knowledge identified about the population biology of this very prevalent infection in tropical and sub-tropical regions around the world. A stochastic individual based stochastic model is described in part to highlight gaps in knowledge. The impact of repeated MDA is simulated to illustrate some aspects of transmission dynamics of this helminth infection. Specifically, the impact and bounce back times in either the intervals between treatment rounds, or post the cessation of treatment, depend critically on the magnitude of two distinct components of the basic reproductive number R0. The absence of data on these key components is highlighted, as is the value of studies of longitudinal cohorts of people in regions of endemic infection post rounds of MDA to record how infection levels bounce back post treatment at individual and population levels of study. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.
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Affiliation(s)
- Benjamin S. Collyer
- Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London, Praed Street, London W2 1PG, UK
| | - Roy Anderson
- Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London, Praed Street, London W2 1PG, UK
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4
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Garira W, Muzhinji K. Application of the replication-transmission relativity theory in the development of multiscale models of infectious disease dynamics. JOURNAL OF BIOLOGICAL DYNAMICS 2023; 17:2255066. [PMID: 37708175 DOI: 10.1080/17513758.2023.2255066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 08/30/2023] [Indexed: 09/16/2023]
Abstract
Despite the existence of a powerful theoretical foundation for the development of multiscale models of infectious disease dynamics in the form of the replication-transmission relativity theory, the majority of current modelling studies focus more on single-scale modelling. The explicit aim of this study is to change the current predominantly single-scale modelling landscape in the design of planning frameworks for the control, elimination and even eradication of infectious disease systems through the exploitation of multiscale modelling methods based on the application of the replication-transmission relativity theory. We first present a structured roadmap for the development of multiscale models of infectious disease systems. The roadmap is tested on hookworm infection. The testing of the feasibility of the roadmap established a fundamental result which can be generalized to confirm that the complexity of an infectious disease system is encapsulated with a level of organization spanning a microscale and a macroscale.
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Affiliation(s)
- Winston Garira
- Modelling Health and Environmental Linkages Research Group (MHELRG), Department of Mathematical and Computational Sciences, University of Venda, Thohoyandou, South Africa
| | - Kizito Muzhinji
- Modelling Health and Environmental Linkages Research Group (MHELRG), Department of Mathematical and Computational Sciences, University of Venda, Thohoyandou, South Africa
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5
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Okoyo C, Orowe I, Onyango N, Montresor A, Mwandawiro C, Medley GF. Optimal control analysis of a transmission interruption model for the soil-transmitted helminth infections in Kenya. CURRENT RESEARCH IN PARASITOLOGY & VECTOR-BORNE DISEASES 2023; 4:100162. [PMID: 38089690 PMCID: PMC10714213 DOI: 10.1016/j.crpvbd.2023.100162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 11/26/2023] [Accepted: 11/27/2023] [Indexed: 02/12/2024]
Abstract
Kenya is among the countries endemic for soil-transmitted helminthiasis (STH) with over 66 subcounties and over 6 million individuals being at-risk of infection. Currently, the country is implementing mass drug administration (MDA) to all the at-risk groups as the mainstay control strategy. This study aimed to develop and analyze an optimal control (OC) model, from a transmission interruption model, to obtain an optimal control strategy from a mix of three strategies evaluated. The study used the Pontryagin's maximum principle to solve, numerically, the OC model. The analysis results clearly demonstrated that water and sanitation when implemented together with the MDA programme offer the best chances of eliminating these tenacious and damaging parasites. Thus, we advocate for optimal implementation of the combined mix of the two interventions in order to achieve STH elimination in Kenya, and globally, in a short implementation period of less than eight years.
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Affiliation(s)
- Collins Okoyo
- School of Mathematics, University of Nairobi, Nairobi, Kenya
- Eastern and Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
- Department of Epidemiology, Statistics and Informatics (DESI), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
| | - Idah Orowe
- School of Mathematics, University of Nairobi, Nairobi, Kenya
| | - Nelson Onyango
- School of Mathematics, University of Nairobi, Nairobi, Kenya
| | - Antonio Montresor
- Department of Control of Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland
| | - Charles Mwandawiro
- Eastern and Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
| | - Graham F. Medley
- Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine (LSHTM), London, United Kingdom
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Bundy DAP, Schultz L, Antoninis M, Barry FBM, Burbano C, Croke K, Drake L, Gyapong J, Karutu C, Kihara J, Lo MM, Makkar P, Mwandawiro C, Ossipow SJ, Bento AR, Rollinson D, Shah H, Turner HC. A positive consequence of the COVID-19 pandemic: how the counterfactual experience of school closures is accelerating a multisectoral response to the treatment of neglected tropical diseases. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220282. [PMID: 37598709 PMCID: PMC10440164 DOI: 10.1098/rstb.2022.0282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 03/07/2023] [Indexed: 08/22/2023] Open
Abstract
Global access to deworming treatment is one of the public health success stories of low-income countries in the twenty-first century. Parasitic worm infections are among the most ubiquitous chronic infections of humans, and early success with mass treatment programmes for these infections was the key catalyst for the neglected tropical disease (NTD) agenda. Since the launch of the 'London Declaration' in 2012, school-based deworming programmes have become the world's largest public health interventions. WHO estimates that by 2020, some 3.3 billion school-based drug treatments had been delivered. The success of this approach was brought to a dramatic halt in April 2020 when schools were closed worldwide in response to the COVID-19 pandemic. These closures immediately excluded 1.5 billion children not only from access to education but also from all school-based health services, including deworming. WHO Pulse surveys in 2021 identified NTD treatment as among the most negatively affected health interventions worldwide, second only to mental health interventions. In reaction, governments created a global Coalition with the twin aims of reopening schools and of rebuilding more resilient school-based health systems. Today, some 86 countries, comprising more than half the world's population, are delivering on this response, and school-based coverage of some key school-based programmes exceeds those from January 2020. This paper explores how science, and a combination of new policy and epidemiological perspectives that began in the 1980s, led to the exceptional growth in school-based NTD programmes after 2012, and are again driving new momentum in response to the COVID-19 pandemic. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.
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Affiliation(s)
- Donald A. P. Bundy
- Research Consortium for School Health and Nutrition, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK
| | - Linda Schultz
- Research Consortium for School Health and Nutrition, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK
| | | | | | | | - Kevin Croke
- Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | | | - John Gyapong
- University of Health and Allied Sciences, PMB 31, Ho, Volta Region, Ghana
| | | | | | | | | | | | | | | | | | | | - Hugo C. Turner
- MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London SW7 2BX, UK
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7
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Collyer BS, Truscott JE, Mwandawiro CS, Njenga SM, Anderson RM. How important is the spatial movement of people in attempts to eliminate the transmission of human helminth infections by mass drug administration? Philos Trans R Soc Lond B Biol Sci 2023; 378:20220273. [PMID: 37598700 PMCID: PMC10440163 DOI: 10.1098/rstb.2022.0273] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Accepted: 04/02/2023] [Indexed: 08/22/2023] Open
Abstract
Human mobility contributes to the spatial dynamics of many infectious diseases, and understanding these dynamics helps us to determine the most effective ways to intervene and plan surveillance. In this paper, we describe a novel transmission model for the spatial dynamics of hookworm, a parasitic worm which is a common infection across sub-Saharan Africa, East Asia and the Pacific islands. We fit our model, with and without mobility, to data obtained from a sub-county in Kenya, and validate the model's predictions against the decline in prevalence observed over the course of a clustered randomized control trial evaluating methods of administering mass chemotherapy. We find that our model which incorporates human mobility is able to reproduce the observed patterns in decline of prevalence during the TUMIKIA trial, and additionally, that the widespread bounce-back of infection may be possible over many years, depending on the rates of people movement between villages. The results have important implications for the design of mass chemotherapy programmes for the elimination of human helminth transmission. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.
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Affiliation(s)
- Benjamin S. Collyer
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, London W2 1PG, UK
| | - James E. Truscott
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, London W2 1PG, UK
| | | | - Sammy M. Njenga
- Eastern and Southern Africa Centre of International Parasite Control, Kenya Medical Research Institute, Nairobi, Kenya
| | - Roy M. Anderson
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, London W2 1PG, UK
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Clark J, Davis EL, Prada JM, Gass K, Krentel A, Hollingsworth TD. How correlations between treatment access and surveillance inclusion impact neglected tropical disease monitoring and evaluation-A simulated study. PLoS Negl Trop Dis 2023; 17:e0011582. [PMID: 37672518 PMCID: PMC10506705 DOI: 10.1371/journal.pntd.0011582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 09/18/2023] [Accepted: 08/09/2023] [Indexed: 09/08/2023] Open
Abstract
Neglected tropical diseases (NTDs) largely impact marginalised communities living in tropical and subtropical regions. Mass drug administration is the leading intervention method for five NTDs; however, it is known that there is lack of access to treatment for some populations and demographic groups. It is also likely that those individuals without access to treatment are excluded from surveillance. It is important to consider the impacts of this on the overall success, and monitoring and evaluation (M&E) of intervention programmes. We use a detailed individual-based model of the infection dynamics of lymphatic filariasis to investigate the impact of excluded, untreated, and therefore unobserved groups on the true versus observed infection dynamics and subsequent intervention success. We simulate surveillance in four groups-the whole population eligible to receive treatment, the whole eligible population with access to treatment, the TAS focus of six- and seven-year-olds, and finally in >20-year-olds. We show that the surveillance group under observation has a significant impact on perceived dynamics. Exclusion to treatment and surveillance negatively impacts the probability of reaching public health goals, though in populations that do reach these goals there are no signals to indicate excluded groups. Increasingly restricted surveillance groups over-estimate the efficacy of MDA. The presence of non-treated groups cannot be inferred when surveillance is only occurring in the group receiving treatment.
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Affiliation(s)
- Jessica Clark
- School of Biodiversity, One Health & Veterinary Medicine, University of Glasgow, Glasgow, Scotland
- Big Data Institute, Neglected Tropical Disease Modelling Consortium, University of Oxford, Oxford, England
| | - Emma L. Davis
- Big Data Institute, Neglected Tropical Disease Modelling Consortium, University of Oxford, Oxford, England
| | - Joaquin M. Prada
- School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, England
| | - Katherine Gass
- Neglected Tropical Diseases Support Center, Task Force for Global Health, Decatur, Georgia, United States of America
| | - Alison Krentel
- School of Epidemiology and Public Health, University of Ottawa, Ottawa, Canada
- Bruyère Research Institute, Ottawa, Canada
| | - T. Déirdre Hollingsworth
- Big Data Institute, Neglected Tropical Disease Modelling Consortium, University of Oxford, Oxford, England
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9
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Cho SY, Hong ST. What was the main factor in successful control of ascariasis in Korea? PARASITES, HOSTS AND DISEASES 2023; 61:103-126. [PMID: 37258258 DOI: 10.3347/phd.22152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Accepted: 11/15/2022] [Indexed: 06/02/2023]
Abstract
In the l950s, under the legacy of traditional agriculture, Ascaris lumbricoides, spread epidemically in the war-bitten society of Korea. Consensus on the parasite control was drafted in the Parasite Disease Prevention Act, which passed a parliamentary agreement in 1966, and established safe disposal of feces and mass chemotherapy as control strategies. Biannual stool examinations and treating infected schoolchildren were basic scheme of the control activity through which revenue could be secured for organized business. In the 27 years following 1969, a maximum of 16 million stool examinations had been done every year. Cellophane thick smear enabled the task. The infection declined remarkably in the 1970s when industrialization and green revolution proceeded. A population study of A. lumbricoides in the late 1970s helped us better understand its epidemiology. The data also settled down the understandable protest of teachers against the repeated stool examinations. In the 9 years following 1987, the target population was gradually reduced when the egg positive rate was below 0.1%. An article in the Korean Law, stipulating obligatory stool examinations, was made optional. Although the long-term Korean effort of Ascaris control was a success, the effect of mass chemotherapy was not as succinct in terms of lowering reinfection. In the period of control, Korean agricultural technology changed, and the economy grew and supplied sanitary facilities by which the vicious cycle was disconnected. Reduction of morbidity was a benefit of mass chemotherapy, which is the only control method feasible in economically difficult countries. The most important hurdle of parasite control in the 1960s was poverty of general population and limited financial resources in Korea but the society formed a consensus on the priority of intestinal helminthiasis control during the ordeal period. The national consensus in the 1960s was the critical milestone for Ascaris control in Korea. Under the social agreement, application of timely technical and research advancements in parasitology achieved the success of ascariasis elimination. The successful experience of ascariasis elimination in Korea can be a benchmark for countries where neglected tropical diseases are endemically recycled.
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Affiliation(s)
- Seung-Yull Cho
- Department of Molecular Parasitology, Sungkyunkwan University, School of Medicine, Suwon 16419, Korea
| | - Sung-Tae Hong
- Department of Tropical Medicine and Parasitology, Seoul National University, College of Medicine, Seoul 03080, Korea
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10
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Anderson RM, Cano J, Hollingsworth TD, Deribe-Kassaye K, Zouré HGM, Kello AB, Impouma B, Kalu AA, Appleby L, Yard E, Salasibew M, McRae-McKee K, Vegvari C. Responding to the cuts in UK AID to neglected tropical diseases control programmes in Africa. Trans R Soc Trop Med Hyg 2023; 117:237-239. [PMID: 36416069 PMCID: PMC9977241 DOI: 10.1093/trstmh/trac109] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/13/2022] [Accepted: 10/27/2022] [Indexed: 11/24/2022] Open
Abstract
The early termination of the Accelerating the Sustainable Control and Elimination of Neglected Tropical Diseases (Ascend) programme by the UK government in June 2021 was a bitter blow to countries in East and West Africa where no alternative source of funding existed. Here we assess the potential impact the cuts may have had if alternative funding had not been made available by new development partners and outline new strategies developed by affected countries to mitigate current and future disruptions to neglected tropical disease control programmes.
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Affiliation(s)
- Roy M Anderson
- Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, London, UK
- Oriole Global Health, London, UK
| | - Jorge Cano
- Expanded Special Project for Elimination of NTDs, World Health Organization Regional Office for Africa, Brazzaville, Republic of the Congo
| | - T Déirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, UK
| | | | - Honorat G M Zouré
- Expanded Special Project for Elimination of NTDs, World Health Organization Regional Office for Africa, Brazzaville, Republic of the Congo
| | - Amir B Kello
- Expanded Special Project for Elimination of NTDs, World Health Organization Regional Office for Africa, Brazzaville, Republic of the Congo
| | - Benido Impouma
- Communicable and Non-communicable Disease Cluster, World Health Organization Regional Office for Africa, Brazzaville, Republic of the Congo
| | - Akpaka A Kalu
- Tropical and vector-borne diseases, World Health Organization Regional Office for Africa, Brazzaville, Republic of the Congo
| | | | | | | | | | - Carolin Vegvari
- Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, London, UK
- Oriole Global Health, London, UK
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11
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Fleitas PE, Kehl SD, Lopez W, Travacio M, Nieves E, Gil JF, Cimino RO, Krolewiecki AJ. Mapping the global distribution of Strongyloides stercoralis and hookworms by ecological niche modeling. Parasit Vectors 2022; 15:197. [PMID: 35676740 PMCID: PMC9178904 DOI: 10.1186/s13071-022-05284-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 04/11/2022] [Indexed: 11/10/2022] Open
Abstract
Background The WHO has established a control strategy for Strongyloides stercoralis in school-aged children as well as targets and to maintain control programs for Ascaris lumbricoides, Trichuris trichiura and hookworms. For an efficient development of control programs, it is necessary to know the target countries around the world, as well as the areas within each country where efforts should be focused. Therefore, maps that provide information on the areas at risk for soil-transmitted helminth (STH) infections on a national and sub-national scale would allow for a better allocation of resources. Methods We used the ecological niche models MaxEnt and Kuenm R library to estimate the global distribution of S. stercoralis and hookworms. We used occurrence points of both species extracted from surveys of two literature reviews and from the Global Atlas of Helminth Infection database, together with 14 raster maps of environmental variables. Results We obtained two raster maps with the presence probability of S. stercoralis and hookworm infections at a global level and then estimated the global population at risk to be 2.6 and 3.4 billion, respectively. The population at risk was also estimated at the country level using estimations for areas as small as 25 km2. A relationship was found between the probability of the presence of S. stercoralis and its prevalence, and a raster map was generated. Annual precipitation, annual temperature, soil carbon content and land cover were the main associated environmental variables. The ecological niches of Strongyloides stercoralis and hookworms had an overlap of 68%. Conclusions Here we provide information that can be used for developing more efficient and integrated control strategies for S. stercoralis and hookworm infections. This information can be annexed to the study of other risk factors or even other diseases to assess the health status of a community. Graphical Abstarct ![]()
Supplementary Information The online version contains supplementary material available at 10.1186/s13071-022-05284-w.
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Affiliation(s)
- Pedro Emanuel Fleitas
- Instituto de Investigaciones de Enfermedades Tropicales (IIET), Sede Regional Orán Universidad Nacional de Salta, Salta, Argentina.,Cátedra de Química Biológica, Facultad de Ciencias Naturales, Universidad Nacional de Salta, Salta, Argentina.,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-CCT Salta, Salta, Argentina
| | - Sebastián Dario Kehl
- Instituto Nacional de Enfermedades Infecciosas, Administración Nacional de Laboratorios e Institutos de Salud "Dr. C. Malbrán", Buenos Aires, Argentina
| | - Walter Lopez
- Instituto de Investigaciones de Enfermedades Tropicales (IIET), Sede Regional Orán Universidad Nacional de Salta, Salta, Argentina
| | - Marina Travacio
- Facultad de Farmacia y Bioquímica, Cátedra de Química General e Inorgánica, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Elvia Nieves
- Instituto de Investigaciones de Enfermedades Tropicales (IIET), Sede Regional Orán Universidad Nacional de Salta, Salta, Argentina
| | - José Fernando Gil
- Instituto de Investigaciones de Enfermedades Tropicales (IIET), Sede Regional Orán Universidad Nacional de Salta, Salta, Argentina.,Cátedra de Química Biológica, Facultad de Ciencias Naturales, Universidad Nacional de Salta, Salta, Argentina.,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-CCT Salta, Salta, Argentina.,Instituto de Investigaciones en Energía No Convencional-CONICET, Salta, Argentina
| | - Rubén Oscar Cimino
- Instituto de Investigaciones de Enfermedades Tropicales (IIET), Sede Regional Orán Universidad Nacional de Salta, Salta, Argentina.,Cátedra de Química Biológica, Facultad de Ciencias Naturales, Universidad Nacional de Salta, Salta, Argentina.,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-CCT Salta, Salta, Argentina
| | - Alejandro Javier Krolewiecki
- Instituto de Investigaciones de Enfermedades Tropicales (IIET), Sede Regional Orán Universidad Nacional de Salta, Salta, Argentina. .,Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-CCT Salta, Salta, Argentina.
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12
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Kura K, Ayabina D, Hollingsworth TD, Anderson RM. Determining the optimal strategies to achieve elimination of transmission for Schistosoma mansoni. Parasit Vectors 2022; 15:55. [PMID: 35164842 PMCID: PMC8842958 DOI: 10.1186/s13071-022-05178-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Accepted: 01/25/2022] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND In January 2021, the World Health Organization published the 2021-2030 roadmap for the control of neglected tropical diseases (NTDs). The goal for schistosomiasis is to achieve elimination as a public health problem (EPHP) and elimination of transmission (EOT) in 78 and 25 countries (by 2030), respectively. Mass drug administration (MDA) of praziquantel continues to be the main strategy for control and elimination. However, as there is limited availability of praziquantel, it is important to determine what volume of treatments are required, who should be targeted and how frequently treatment must be administered to eliminate either transmission or morbidity caused by infection in different endemic settings with varied transmission intensities. METHODS AND RESULTS: In this paper, we employ two individual-based stochastic models of schistosomiasis transmission developed independently by the Imperial College London (ICL) and University of Oxford (SCHISTOX) to determine the optimal treatment strategies to achieve EOT. We find that treating school-age children (SAC) only is not sufficient to achieve EOT within a feasible time frame, regardless of the transmission setting and observed age-intensity of infection profile. Both models show that community-wide treatment is necessary to interrupt transmission in all endemic settings with low, medium and high pristine transmission intensities. CONCLUSIONS The required MDA coverage level to achieve either transmission or morbidity elimination depends on the prevalence prior to the start of treatment and the burden of infection in adults. The higher the worm burden in adults, the higher the coverage levels required for this age category through community-wide treatment programmes. Therefore, it is important that intensity and prevalence data are collected in each age category, particularly from SAC and adults, so that the correct coverage level can be calculated and administered.
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Affiliation(s)
- Klodeta Kura
- grid.512598.2London Centre for Neglected Tropical Disease Research, London, UK ,grid.7445.20000 0001 2113 8111Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, UK ,grid.14105.310000000122478951MRC Centre for Global Infectious Disease Analysis, London, UK
| | - Diepreye Ayabina
- grid.4991.50000 0004 1936 8948Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, OX3 7LF UK
| | - T. Deirdre Hollingsworth
- grid.4991.50000 0004 1936 8948Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, OX3 7LF UK
| | - Roy M. Anderson
- grid.512598.2London Centre for Neglected Tropical Disease Research, London, UK ,grid.7445.20000 0001 2113 8111Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, UK ,grid.14105.310000000122478951MRC Centre for Global Infectious Disease Analysis, London, UK ,grid.35937.3b0000 0001 2270 9879The DeWorm3 Project, The Natural History Museum of London, London, UK
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13
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Kura K, Hardwick RJ, Truscott JE, Anderson RM. What is the impact of acquired immunity on the transmission of schistosomiasis and the efficacy of current and planned mass drug administration programmes? PLoS Negl Trop Dis 2021; 15:e0009946. [PMID: 34851952 PMCID: PMC8635407 DOI: 10.1371/journal.pntd.0009946] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2020] [Accepted: 10/23/2021] [Indexed: 11/18/2022] Open
Abstract
Schistosomiasis causes severe morbidity in many countries with endemic infection with the schistosome digenean parasites in Africa and Asia. To control and eliminate the disease resulting from infection, regular mass drug administration (MDA) is used, with a focus on school-aged children (SAC; 5-14 years of age). In some high transmission settings, the World Health Organization (WHO) also recommends the inclusion of at-risk adults in MDA treatment programmes. The question of whether ecology (age-dependant exposure) or immunity (resistance to reinfection), or some combination of both, determines the form of observed convex age-intensity profile is still unresolved, but there is a growing body of evidence that the human hosts acquire some partial level of immunity after a long period of repeated exposure to infection. In the majority of past research modelling schistosome transmission and the impact of MDA programmes, the effect of acquired immunity has not been taken into account. Past work has been based on the assumption that age-related contact rates generate convex horizontal age-intensity profiles. In this paper, we use an individual based stochastic model of transmission and MDA impact to explore the effect of acquired immunity in defined MDA programmes. Compared with scenarios with no immunity, we find that acquired immunity makes the MDA programme less effective with a slower decrease in the prevalence of infection. Therefore, the time to achieve morbidity control and elimination as a public health problem is longer than predicted by models with just age-related exposure and no build-up of immunity. The level of impact depends on the baseline prevalence prior to treatment (the magnitude of the basic reproductive number R0) and the treatment frequency, among other factors. We find that immunity has a larger impact within moderate to high transmission settings such that it is very unlikely to achieve morbidity and transmission control employing current MDA programmes.
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Affiliation(s)
- Klodeta Kura
- London Centre for Neglected Tropical Disease Research, London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, London, United Kingdom
| | - Robert J. Hardwick
- London Centre for Neglected Tropical Disease Research, London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, London, United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, United Kingdom
| | - James E. Truscott
- London Centre for Neglected Tropical Disease Research, London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, London, United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, United Kingdom
| | - Roy M. Anderson
- London Centre for Neglected Tropical Disease Research, London, United Kingdom
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- MRC Centre for Global Infectious Disease Analysis, London, United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, United Kingdom
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14
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The yin and yang of human soil-transmitted helminth infections. Int J Parasitol 2021; 51:1243-1253. [PMID: 34774540 PMCID: PMC9145206 DOI: 10.1016/j.ijpara.2021.11.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 11/01/2021] [Accepted: 11/02/2021] [Indexed: 12/22/2022]
Abstract
The major soil-transmitted helminths that infect humans are the roundworms, whipworms and hookworms. Soil-transmitted helminth infections rank among the most important neglected tropical diseases in terms of morbidity, and almost one billion people are still infected with at least one species. While anthelmintic drugs are available, they do not offer long term protection against reinfection, precipitating the need for vaccines that provide long-term immunologic defense. Vaccine discovery and development is in advanced clinical development for hookworm infection, with a bivalent human hookworm vaccine in clinical trials in Brazil and Africa, but is in its infancy for both roundworm (ascariasis) and whipworm (trichuriasis) infections. One of the greatest hurdles to developing soil-transmitted helminth vaccines is the potent immunoregulatory properties of these helminths, creating a barrier to the induction of meaningful long-term protective immunity. While challenging for vaccinologists, this phenomenon presents unique opportunities to develop an entirely new class of anti-inflammatory drugs that capitalise on these immunomodulatory strategies. Epidemiologic studies and clinical trials employing experimental soil-transmitted helminth challenge models, when coupled with findings from animal models, show that at least some soil-transmitted helminth-derived molecules can protect against the onset of autoimmune, allergic and metabolic disorders, and several natural products with the desired bioactivity have been isolated and tested in pre-clinical settings. The yin and yang of soil-transmitted helminth infections reflect both the urgency for effective vaccines and the potential for new immunoregulatory molecules from parasite products.
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15
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Anderson RM. An urgent need: vaccines for neglected tropical diseases. THE LANCET INFECTIOUS DISEASES 2021; 21:1621-1623. [PMID: 34419210 PMCID: PMC8376208 DOI: 10.1016/s1473-3099(21)00260-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 04/14/2021] [Indexed: 11/23/2022]
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16
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O'Neal SE, Pray IW, Vilchez P, Gamboa R, Muro C, Moyano LM, Ayvar V, Gavidia CM, Gilman RH, Gonzalez AE, Garcia HH. Geographically Targeted Interventions versus Mass Drug Administration to Control Taenia solium Cysticercosis, Peru. Emerg Infect Dis 2021; 27:2389-2398. [PMID: 34424165 PMCID: PMC8386790 DOI: 10.3201/eid2709.203349] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Optimal control strategies for Taenia solium taeniasis and cysticercosis have not been determined. We conducted a 2-year cluster randomized trial in Peru by assigning 23 villages to 1 of 3 geographically targeted intervention approaches. For ring screening (RS), participants living near pigs with cysticercosis were screened for taeniasis; identified cases were treated with niclosamide. In ring treatment (RT), participants living near pigs with cysticercosis received presumptive treatment with niclosamide. In mass treatment (MT), participants received niclosamide treatment every 6 months regardless of location. In each approach, half the villages received targeted or mass oxfendazole for pigs (6 total study arms). We noted significant reductions in seroincidence among pigs in all approaches (67.1% decrease in RS, 69.3% in RT, 64.7% in MT; p<0.001), despite a smaller proportion of population treated by targeted approaches (RS 1.4%, RT 19.3%, MT 88.5%). Our findings suggest multiple approaches can achieve rapid control of T. solium transmission.
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17
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Molyneux DH, Asamoa-Bah A, Fenwick A, Savioli L, Hotez P. The history of the neglected tropical disease movement. Trans R Soc Trop Med Hyg 2021; 115:169-175. [PMID: 33508096 PMCID: PMC7842098 DOI: 10.1093/trstmh/trab015] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Revised: 01/07/2021] [Accepted: 01/13/2021] [Indexed: 01/05/2023] Open
Abstract
The history of the neglected tropical disease movement is seen through the lens of authors who worked during the last 4 decades in different roles and in different settings, from Western-based laboratories to clinical roles in endemic countries and in critical policy roles in the World Health Organization (WHO). The authors seek to identify key players from the introduction of the word 'neglected' by the late Kenneth Warren in his Rockefeller Foundation-supported Great Neglected Diseases of Mankind movement through to the more recent developments after the London Declaration of 2012. The role of the various actors-endemic countries, major pharmaceutical companies, the WHO, non-government development organizations, bilateral donors and academia-are discussed. The critical events and decisions are highlighted that were essential enabling factors in creating a viable and successful movement and with a resultant massive global public health and antipoverty impact. The importance of advocacy is emphasized in creating the momentum to establish a globally recognized public health 'brand' as a target in the United Nations Sustainable Development Goals.
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Affiliation(s)
- David H Molyneux
- Department of Tropical Disease Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
| | | | - Alan Fenwick
- School of Public Health Imperial College Norfolk Place W2 1PG, UK
| | - Lorenzo Savioli
- P.O. Box 267, Chake Chake, Pemba Island, Zanzibar, United Republic of Tanzania
| | - Peter Hotez
- National School of Tropical Medicine, Baylor College of Medicine, Houston, TX 77030, USA
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18
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Spatial scales in human movement between reservoirs of infection. J Theor Biol 2021; 524:110726. [PMID: 33895180 PMCID: PMC8204271 DOI: 10.1016/j.jtbi.2021.110726] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 04/09/2021] [Accepted: 04/12/2021] [Indexed: 11/22/2022]
Abstract
Simple, yet flexible, model of human movement patterns. Analytic formalism which can be used to derive important spatial scales. Introduces a novel drift–diffusion approximation for stochastic reservoirs. A new critical spatial scale predicted for helminth reservoirs of infection. The necessary data needed to test these predictions is outlined in detail.
The life cycle of parasitic organisms that are the cause of much morbidity in humans often depend on reservoirs of infection for transmission into their hosts. Understanding the daily, monthly and yearly movement patterns of individuals between reservoirs is therefore of great importance to implementers of control policies seeking to eliminate various parasitic diseases as a public health problem. This is due to the fact that the underlying spatial extent of the reservoir of infection, which drives transmission, can be strongly affected by inputs from external sources, i.e., individuals who are not spatially attributed to the region defined by the reservoir itself can still migrate and contribute to it. In order to study the importance of these effects, we build and examine a novel theoretical model of human movement between spatially-distributed focal points for infection clustered into regions defined as ‘reservoirs of infection’. Using our model, we vary the spatial scale of human moment defined around focal points and explicitly calculate how varying this definition can influence the temporal stability of the effective transmission dynamics – an effect which should strongly influence how control measures, e.g., mass drug administration (MDA), define evaluation units (EUs). Considering the helminth parasites as our main example, by varying the spatial scale of human movement, we demonstrate that a critical scale exists around infectious focal points at which the migration rate into their associated reservoir can be neglected for practical purposes. This scale varies by species and geographic region, but is generalisable as a concept to infectious reservoirs of varying spatial extents and shapes. Our model is designed to be applicable to a very general pattern of infectious disease transmission modified by the migration of infected individuals between clustered communities. In particular, it may be readily used to study the spatial structure of hosts for macroparasites with temporally stationary distributions of infectious focal point locations over the timescales of interest, which is viable for the soil-transmitted helminths and schistosomes. Additional developments will be necessary to consider diseases with moving reservoirs, such as vector-born filarial worm diseases.
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19
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Collyer BS, Anderson RM. Probability distributions of helminth parasite burdens within the human host population following repeated rounds of mass drug administration and their impact on the transmission breakpoint. J R Soc Interface 2021; 18:20210200. [PMID: 33906385 PMCID: PMC8086906 DOI: 10.1098/rsif.2021.0200] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 04/06/2021] [Indexed: 01/14/2023] Open
Abstract
The existence of multiple stable equilibria in models of parasitic helminth transmission was a ground-breaking discovery over 30 years ago. An implication of this discovery, that there is a level of infection below which transmission cannot self-sustain called the transmission breakpoint, has in part motivated the push towards the elimination of many human diseases caused by the multiple species of helminth worldwide. In the absence of vaccines, the predominant method in this push towards elimination is to repeatedly administer endemic populations with anthelmintic drugs, over several treatment rounds, in what has become to be known as mass drug administration (MDA). MDA will inevitably alter the distribution of parasite burdens among hosts from the baseline distribution, and significantly, the location of the transmission breakpoint is known to be dependent on the level of aggregation of this distribution-for a given mean worm burden, more highly aggregated distributions where fewer individuals harbour most of the burden, will have a lower transmission breakpoint. In this paper, we employ a probabilistic analysis of the changes to the distribution of burdens in a population undergoing MDA, and simple approximations, to determine how key aspects of the programmes (including compliance, drug efficacy and treatment coverage) affect the location of the transmission breakpoint. We find that individual compliance to treatment, which determines the number of times an individual participates in mass drug administration programmes, is key to the location of the breakpoint, indicating the vital importance to ensure that people are not routinely missed in these programmes.
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Affiliation(s)
- Benjamin S. Collyer
- MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, London, UK
| | - Roy M. Anderson
- MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, London, UK
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20
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Deslyper G, Murphy DM, Sowemimo OA, Holland CV, Doherty DG. Distinct hepatic myeloid and lymphoid cell repertoires are associated with susceptibility and resistance to Ascaris infection. Parasitology 2021; 148:539-549. [PMID: 33431071 PMCID: PMC10090783 DOI: 10.1017/s0031182021000020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 01/05/2021] [Accepted: 01/06/2021] [Indexed: 02/02/2023]
Abstract
The soil-transmitted helminth Ascaris lumbricoides infects ~800 million people worldwide. Some people are heavily infected, harbouring many worms, whereas others are only lightly infected. The mechanisms behind this difference are unknown. We used a mouse model of hepatic resistance to Ascaris, with C57BL/6J mice as a model for heavy infection and CBA/Ca mice as a model for light infection. The mice were infected with the porcine ascarid, Ascaris suum or the human ascarid, A. lumbricoides and immune cells in their livers and spleens were enumerated using flow cytometry. Compared to uninfected C57BL/6J mice, uninfected CBA/Ca mice had higher splenic CD4+ and γδ T cell counts and lower hepatic eosinophil, Kupffer cell and B cell counts. Infection with A. suum led to expansions of eosinophils, Kupffer cells, monocytes and dendritic cells in the livers of both mouse strains and depletions of hepatic natural killer (NK) cells in CBA/Ca mice only. Infection with A. lumbricoides led to expansions of hepatic eosinophils, monocytes and dendritic cells and depletions of CD8+, αβ, NK and NK T cells in CBA/Ca mice, but not in C57BL/6J mice where only monocytes expanded. Thus, susceptibility and resistance to Ascaris infection are governed, in part, by the hepatic immune system.
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Affiliation(s)
- Gwendoline Deslyper
- Department of Zoology, School of Natural Sciences, Trinity College Dublin, Dublin, Ireland
| | - Dearbhla M. Murphy
- Department of Immunology, School of Medicine, Trinity College Dublin, Dublin, Ireland
| | | | - Celia V. Holland
- Department of Zoology, School of Natural Sciences, Trinity College Dublin, Dublin, Ireland
| | - Derek G. Doherty
- Department of Immunology, School of Medicine, Trinity College Dublin, Dublin, Ireland
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21
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Okoyo C, Medley G, Mwandawiro C, Onyango N. Modeling the Interruption of the Transmission of Soil-Transmitted Helminths Infections in Kenya: Modeling Deworming, Water, and Sanitation Impacts. Front Public Health 2021; 9:637866. [PMID: 33842421 PMCID: PMC8024473 DOI: 10.3389/fpubh.2021.637866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Accepted: 03/01/2021] [Indexed: 11/13/2022] Open
Abstract
Kenya, just like other countries with endemic soil-transmitted helminths (STH), has conducted regular mass drug administration (MDA) program for the last 5 years among school aged children as a way to reduce STH infections burden in the country. However, the point of interruption of transmission of these infections still remains unclear. In this study, we developed and analyzed an age structured mathematical model to predict the elimination period (i.e., time taken to interrupt STH transmission) of these infections in Kenya. The study utilized a deterministic age structured model of the STH population dynamics under a regular treatment program. The model was applied to three main age groups: pre-school age children (2-4 years), school age children (5-14 years), and adult populations (≥15 years) and compared the impact of two interventions on worm burden and elimination period. The model-simulated results were compared with the 5 year field data from the Kenyan deworming program for all the three types of STH (Ascaris lumbricoides, Trichuris trichiura, and hookworm). The model demonstrated that the reduction of worm burden and elimination period depended heavily on four parameter groups; drug efficacy, number of treatment rounds, MDA and water, sanitation and hygiene (WASH) coverage. The analysis showed that for STH infections to be eliminated using MDA alone in a short time period, 3-monthly MDA plan is desired. However, complementation of MDA with WASH at an optimal (95%) coverage level was most effective. These results are important to the Kenyan STH control program as it will guide the recently launched Breaking Transmission Strategy.
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Affiliation(s)
- Collins Okoyo
- Eastern and Southern Africa Centre of International Parasite Control, Kenya Medical Research Institute, Nairobi, Kenya
- School of Mathematics, University of Nairobi, Nairobi, Kenya
| | - Graham Medley
- Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Charles Mwandawiro
- Eastern and Southern Africa Centre of International Parasite Control, Kenya Medical Research Institute, Nairobi, Kenya
| | - Nelson Onyango
- School of Mathematics, University of Nairobi, Nairobi, Kenya
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22
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Seasonal distribution and environmental parameters associated with Brugia pahangi and Dirofilaria immitis in naturally infected dogs in Bangkok and vicinity, Thailand. Sci Rep 2021; 11:4594. [PMID: 33633276 PMCID: PMC7907406 DOI: 10.1038/s41598-021-84215-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 02/12/2021] [Indexed: 12/12/2022] Open
Abstract
Dirofilaria immitis and Brugia pahangi are vector-borne parasites found in dogs and cats, including Thailand. In order to evaluate the effects of season and environmental parameters on the prevalence of these parasites, this retrospective study was conducted in 2019. A total of 79,506 canine blood samples were examined. B. pahangi was found in 0.55% of samples (438/79,506; 95% CI 0.50–0.61) while D. immitis was detected in 0.43% (345/79,506; 95% CI 0.39–0.48). One-way ANOVA found no effect of seasonal conditions on prevalence. For B. pahangi, the parameters rainfall, relative humidity and sunshine hours showed associations with p ≤ 0.20 and were included in multiple logistic regressions resulting in adjusted odds ratios of 0.53, 1.31 and 0.55, respectively. For D. immitis, only average temperature showed p ≤ 0.20, resulting in an odds ratio of 0.42. In conclusion, Thailand has environmental parameters that do not change very much during the year, so they might not affect the prevalence of two filarial nematodes. However, the threat of B. pahangi and D. immitis should not be ignored, especially in subtropical regions where their vectors are abundant. Both owners and veterinarians should be concerned about filarial prevention and control of D. immitis and B. pahangi.
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23
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Graham M, Ayabina D, Lucas TC, Collyer BS, Medley GF, Hollingsworth TD, Toor J. SCHISTOX: An individual based model for the epidemiology and control of schistosomiasis. Infect Dis Model 2021; 6:438-447. [PMID: 33665519 PMCID: PMC7897994 DOI: 10.1016/j.idm.2021.01.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Accepted: 01/21/2021] [Indexed: 02/08/2023] Open
Abstract
A stochastic individual based model, SCHISTOX, has been developed for the study of schistosome transmission dynamics and the impact of control by mass drug administration. More novel aspects that can be investigated include individual level adherence and access to treatment, multiple communities, human sex population dynamics, and implementation of a potential vaccine. Many of the model parameters have been estimated within previous studies and have been shown to vary between communities, such as the age-specific contact rates governing the age profiles of infection. However, uncertainty remains as there are wide ranges for certain parameter values and a few remain relatively unknown. We analyse the model dynamics by parameterizing it with published parameter values. We also discuss the development of SCHISTOX in the form of a publicly available open-source GitHub repository. The next key development stage involves validating the model by calibrating to epidemiological data.
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Affiliation(s)
- Matthew Graham
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom.,Centre for Mathematical Modelling of Infectious Disease, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Diepreye Ayabina
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom
| | - Tim Cd Lucas
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom.,Centre for Environment and Health, Imperial College London, London, United Kingdom
| | - Benjamin S Collyer
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, United Kingdom
| | - Graham F Medley
- Centre for Mathematical Modelling of Infectious Disease, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - T Deirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom
| | - Jaspreet Toor
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom.,MRC Centre for Global Infectious Disease Analysis; and the Abdul Latif Jameel Institute for Disease and Emergency Analytics (J-IDEA), School of Public Health, Imperial College London, London, W2 1PG, United Kingdom
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24
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Hardwick RJ, Werkman M, Truscott JE, Anderson RM. Stochastic challenges to interrupting helminth transmission. Epidemics 2021; 34:100435. [PMID: 33571786 DOI: 10.1016/j.epidem.2021.100435] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 07/27/2020] [Accepted: 01/10/2021] [Indexed: 01/29/2023] Open
Abstract
Predicting the effect of different programmes designed to control both the morbidity induced by helminth infections and parasite transmission is greatly facilitated by the use of mathematical models of transmission and control impact. In such models, it is essential to account for the many sources of uncertainty - natural, or otherwise - to ensure robustness in prediction and to accurately depict variation around an expected outcome. In this paper, we investigate how well the standard deterministic models match the predictions made using individual-based stochastic simulations. We also explore how well concepts which derive from deterministic models, such as 'breakpoints' in transmission, apply in the stochastic world. Employing an individual-based stochastic model framework we also investigate how transmission and control are affected by the migration of infected people into a defined community. To give our study focus we consider the control of soil-transmitted helminths (STH) by mass drug administration (MDA), though our methodology is readily applicable to the other helminth species such as the schistosome parasites and the filarial worms. We show it is possible to theoretically define a 'stochastic breakpoint' where much noise surrounds the expected deterministic breakpoint. We also discuss the concept of the 'interruption of transmission' independent of the 'breakpoint' concept where analyses of model behaviour illustrate the current limitations of deterministic models to account for the 'fade-out' or transmission extinction behaviour in simulations. Our analysis of migration confirms a relationship between the critical infected human migration rate scale (i.e., order of magnitude) per unit of time and the death rate of infective stages that are released into the free-living environment. This relationship is shown to determine the likelihood that control activities aim at chemotherapeutic treatment of the human host will eliminate transmission. The development of a new stochastic simulation code for STH in the form of a publicly-available open-source python package which includes features to incorporate many population stratifications, different control interventions including mass drug administration (with defined frequency, coverage levels and compliance patterns) and inter-village human migration is also described.
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Affiliation(s)
- Robert J Hardwick
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1PG, UK; The DeWorm3 Project, the Natural History Museum of London, London SW7 5BD, UK; MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, UK.
| | - Marleen Werkman
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1PG, UK; The DeWorm3 Project, the Natural History Museum of London, London SW7 5BD, UK; MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, UK
| | - James E Truscott
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1PG, UK; The DeWorm3 Project, the Natural History Museum of London, London SW7 5BD, UK; MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, UK
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1PG, UK; The DeWorm3 Project, the Natural History Museum of London, London SW7 5BD, UK; MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, UK
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25
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Abstract
AbstractReproduction, mortality, and immune function often change with age but do not invariably deteriorate. Across the tree of life, there is extensive variation in age-specific performance and changes to key life-history traits. These changes occur on a spectrum from classic senescence, where performance declines with age, to juvenescence, where performance improves with age. Reproduction, mortality, and immune function are also important factors influencing the spread of infectious disease, yet there exists no comprehensive investigation into how the aging spectrum of these traits impacts epidemics. We used a model laboratory infection system to compile an aging profile of a single organism, including traits directly linked to pathogen susceptibility and those that should indirectly alter pathogen transmission by influencing demography. We then developed generalizable epidemiological models demonstrating that different patterns of aging produce dramatically different transmission landscapes: in many cases, aging can reduce the probability of epidemics, but it can also promote severity. This work provides context and tools for use across taxa by empiricists, demographers, and epidemiologists, advancing our ability to accurately predict factors contributing to epidemics or the potential repercussions of senescence manipulation.
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26
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Huang Q, Gurarie D, Ndeffo-Mbah M, Li E, King CH. Schistosoma transmission in a dynamic seasonal environment and its impact on the effectiveness of disease control. J Infect Dis 2020; 225:1050-1061. [PMID: 33263735 PMCID: PMC8921996 DOI: 10.1093/infdis/jiaa746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Accepted: 11/30/2020] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND A seasonal transmission environment including seasonal variation of snail population density and human-snail contact patterns can affect the dynamics of Schistosoma infection and the success of control interventions. In projecting control outcomes, conventional modeling approaches have often ignored seasonality by using simplified intermediate-host modeling, or by restricting seasonal effects through use of yearly averaging. METHODS We used mathematical analysis and numerical simulation to estimate the impact of seasonality on disease dynamics and control outcomes, and to evaluate whether seasonal averaging or intermediate-host reduction can provide reliable predictions of control outcomes. We also examined whether seasonality could be used as leverage in creation of effective control strategies. RESULTS We found models that used seasonal averaging could grossly overestimate infection burden and underestimate control outcomes in highly seasonal environments. We showed that proper intra-seasonal timing of control measures could make marked improvement on the long-term burden reduction for Schistosoma transmission control, and we identified the optimal timing for each intervention. Seasonal snail control, implemented alone, was less effective than mass drug administration, but could provide additive impact in reaching control and elimination targets. CONCLUSION Seasonal variation makes Schistosoma transmission less sustainable and easier to control than predicted by earlier modeling studies.
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Affiliation(s)
- Qimin Huang
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA
| | - David Gurarie
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, Cleveland, USA.,Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, Cleveland, USA
| | - Martial Ndeffo-Mbah
- Department of Veterinary and Integrative Biosciences, College of Veterinary and Biomedical Sciences, Texas A&M University, College Station, USA.,School of Public Health, Texas A&M University, College Station, USA
| | - Emily Li
- Ascension St. Vincent Indianapolis, Family Medicine Residency, Indianapolis, USA
| | - Charles H King
- Center for Global Health and Diseases, School of Medicine, Case Western Reserve University, Cleveland, USA.,Schistosomiasis Consortium for Operational Research and Evaluation, University of Georgia, Athens, USA.,WHO Collaborating Centre for Research and Training for Schistosomiasis Elimination, Cleveland, USA
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27
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Lambura AG, Mwanga GG, Luboobi L, Kuznetsov D. Mathematical Model for Optimal Control of Soil-Transmitted Helminth Infection. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2020; 2020:6721919. [PMID: 32802152 PMCID: PMC7416292 DOI: 10.1155/2020/6721919] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/14/2020] [Revised: 05/11/2020] [Accepted: 06/19/2020] [Indexed: 02/01/2023]
Abstract
In this paper, we study the dynamics of soil-transmitted helminth infection. We formulate and analyse a deterministic compartmental model using nonlinear differential equations. The basic reproduction number is obtained and both disease-free and endemic equilibrium points are shown to be asymptotically stable under given threshold conditions. The model may exhibit backward bifurcation for some parameter values, and the sensitivity indices of the basic reproduction number with respect to the parameters are determined. We extend the model to include control measures for eradication of the infection from the community. Pontryagian's maximum principle is used to formulate the optimal control problem using three control strategies, namely, health education through provision of educational materials, educational messages to improve the awareness of the susceptible population, and treatment by mass drug administration that target the entire population(preschool- and school-aged children) and sanitation through provision of clean water and personal hygiene. Numerical simulations were done using MATLAB and graphical results are displayed. The cost effectiveness of the control measures were done using incremental cost-effective ratio, and results reveal that the combination of health education and sanitation is the best strategy to combat the helminth infection. Therefore, in order to completely eradicate soil-transmitted helminths, we advise investment efforts on health education and sanitation controls.
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Affiliation(s)
- Aristide G. Lambura
- School of Computational and Communication Science and Engineering, The Nelson Mandela African, Institution of Science and Technology, P.O. Box 447, Arusha-, Tanzania
- Department of Computer Systems and Mathemmatics, Ardhi University, P.O. Box 35176, Dar es Salaam, Tanzania
| | - Gasper G. Mwanga
- Department of Physcics, Mathematics and Informatics, University of Dar es Salaam, P.O. Box 2329, Dar es Salaam, Tanzania
| | - Livingstone Luboobi
- School of Computational and Communication Science and Engineering, The Nelson Mandela African, Institution of Science and Technology, P.O. Box 447, Arusha-, Tanzania
- Institute of Mathematical Sciences, Strathmore University, P.O. Box 59857-00200, Nairobi, Kenya
| | - Dmitry Kuznetsov
- School of Computational and Communication Science and Engineering, The Nelson Mandela African, Institution of Science and Technology, P.O. Box 447, Arusha-, Tanzania
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28
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Werkman M, Wright JE, Truscott JE, Oswald WE, Halliday KE, Papaiakovou M, Farrell SH, Pullan RL, Anderson RM. The impact of community-wide, mass drug administration on aggregation of soil-transmitted helminth infection in human host populations. Parasit Vectors 2020; 13:290. [PMID: 32513254 PMCID: PMC7278197 DOI: 10.1186/s13071-020-04149-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Accepted: 05/25/2020] [Indexed: 11/21/2022] Open
Abstract
Background Soil-transmitted helminths (STH) are intestinal parasites estimated to infect over 1.5 billion people. Current treatment programmes are aimed at morbidity control through school-based deworming programmes (targeting school-aged children, SAC) and treating women of reproductive age (WRA), as these two groups are believed to record the highest morbidity. More recently, however, the potential for interrupting transmission by treating entire communities has been receiving greater emphasis and the feasibility of such programmes are now under investigation in randomised clinical trials through the Bill & Melinda Gates Foundation funded DeWorm3 studies. Helminth parasites are known to be highly aggregated within human populations, with a small minority of individuals harbouring most worms. Empirical evidence from the TUMIKIA project in Kenya suggests that aggregation may increase significantly after anthelminthic treatment. Methods A stochastic, age-structured, individual-based simulation model of parasite transmission is employed to better understand the factors that might induce this pattern. A simple probabilistic model based on compounded negative binomial distributions caused by age-dependencies in both treatment coverage and exposure to infection is also employed to further this understanding. Results Both approaches confirm helminth aggregation is likely to increase post-mass drug administration as measured by a decrease in the value of the negative binomial aggregation parameter, k. Simple analytical models of distribution compounding describe the observed patterns well. Conclusions The helminth aggregation that was observed in the field was replicated with our stochastic individual-based model. Further work is required to generalise the probabilistic model to take account of the respective sensitivities of different diagnostics on the presence or absence of infection.![]()
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Affiliation(s)
- Marleen Werkman
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London, UK. .,The DeWorm3 Project, The Natural History Museum of London, London, UK. .,MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK.
| | - James E Wright
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London, UK.,The DeWorm3 Project, The Natural History Museum of London, London, UK.,MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK.,Centre for Global Child Health, Hospital for Sick Children, Toronto, Canada
| | - James E Truscott
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London, UK.,The DeWorm3 Project, The Natural History Museum of London, London, UK.,MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK
| | - William E Oswald
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
| | - Katherine E Halliday
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
| | - Marina Papaiakovou
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London, UK.,MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK.,Department of Life Sciences, Natural History Museum, London, UK
| | - Sam H Farrell
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London, UK
| | - Rachel L Pullan
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London, UK.,The DeWorm3 Project, The Natural History Museum of London, London, UK.,MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK
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29
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Toor J, Alsallaq R, Truscott JE, Turner HC, Werkman M, Gurarie D, King CH, Anderson RM. Are We on Our Way to Achieving the 2020 Goals for Schistosomiasis Morbidity Control Using Current World Health Organization Guidelines? Clin Infect Dis 2019; 66:S245-S252. [PMID: 29860290 PMCID: PMC5982704 DOI: 10.1093/cid/ciy001] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Background Schistosomiasis remains an endemic parasitic disease affecting millions of people around the world. The World Health Organization (WHO) has set goals of controlling morbidity to be reached by 2020, along with elimination as a public health problem in certain regions by 2025. Mathematical models of parasite transmission and treatment impact have been developed to assist in controlling the morbidity caused by schistosomiasis. These models can inform and guide implementation policy for mass drug administration programs, and help design monitoring and evaluation activities. Methods We use these models to predict whether the guidelines set by the WHO are on track for achieving their 2020 goal for the control of morbidity, specifically for Schistosoma mansoni. We examine whether programmatic adaptations; namely increases in treatment coverage and/or expansion to adult inclusion in treatment, will improve the likelihood of reaching the WHO goals. Results We find that in low-prevalence settings, the goals are likely to be attainable under current WHO guidelines, but in moderate to high-prevalence settings, the goals are less likely to be achieved unless treatment coverage is increased and expanded to at least 85% for school-aged children and 40% for adults. Conclusions To improve the likelihood of reaching the WHO goals, programmatic adaptations are required, particularly for moderate- to high-prevalence settings. Furthermore, improvements in adherence to treatment, potential development of candidate vaccines, and enhanced snail control and WASH (water, sanitation, and hygiene) measures will all assist in achieving the goals.
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Affiliation(s)
- Jaspreet Toor
- London Centre for Neglected Tropical Disease Research, Imperial College London, United Kingdom.,Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, United Kingdom
| | - Ramzi Alsallaq
- Center for Global Health and Diseases and Department of Mathematics, Case Western Reserve University, Cleveland, Ohio
| | - James E Truscott
- London Centre for Neglected Tropical Disease Research, Imperial College London, United Kingdom.,Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, United Kingdom.,The DeWorm3 Project, Natural History Museum of London, United Kingdom
| | - Hugo C Turner
- Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Programme, Ho Chi Minh City, Vietnam.,Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, United Kingdom
| | - Marleen Werkman
- London Centre for Neglected Tropical Disease Research, Imperial College London, United Kingdom.,Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, United Kingdom.,The DeWorm3 Project, Natural History Museum of London, United Kingdom
| | - David Gurarie
- Center for Global Health and Diseases and Department of Mathematics, Case Western Reserve University, Cleveland, Ohio
| | - Charles H King
- Center for Global Health and Diseases and Department of Mathematics, Case Western Reserve University, Cleveland, Ohio
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research, Imperial College London, United Kingdom.,Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, United Kingdom.,The DeWorm3 Project, Natural History Museum of London, United Kingdom
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30
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Garira W. The Replication-Transmission Relativity Theory for Multiscale Modelling of Infectious Disease Systems. Sci Rep 2019; 9:16353. [PMID: 31705140 PMCID: PMC6841738 DOI: 10.1038/s41598-019-52820-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 10/24/2019] [Indexed: 12/19/2022] Open
Abstract
It is our contention that for multiscale modelling of infectious disease systems to evolve and expand in scope, it needs to be founded on a theory. Such a theory would improve our ability to describe infectious disease systems in terms of their scales and levels of organization, and their inter-relationships. In this article we present a relativistic theory for multiscale modelling of infectious disease systems, that can be considered as an extension of the relativity principle in physics, called the replication-transmission relativity theory. This replication-transmission relativity theory states that at any level of organization of an infectious disease system there is no privileged/absolute scale which would determine, disease dynamics, only interactions between the microscale and macroscale. Such a relativistic theory provides a scientific basis for a systems level description of infectious disease systems using multiscale modelling methods. The central idea of this relativistic theory is that at every level of organization of an infectious disease system, the reciprocal influence between the microscale and the macroscale establishes a pathogen replication-transmission multiscale cycle. We distinguish two kinds of reciprocal influence between the microscale and the macroscale based on systematic differences in their conditions of relevancy. Evidence for the validity of the replication-transmission relativity theory is presented using a multiscale model of hookworm infection that is developed at host level when the relationship between the microscale and the macroscale is described by one of the forms of reciprocal influence.
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Affiliation(s)
- Winston Garira
- Modelling Health and Environmental Linkages Research Group (MHELRG), Department of Mathematics and Applied Mathematics, University of Venda, Private Bag X5050, Thohoyandou, 0950, South Africa.
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31
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Collyer BS, Turner HC, Hollingsworth TD, Keeling MJ. Vaccination or mass drug administration against schistosomiasis: a hypothetical cost-effectiveness modelling comparison. Parasit Vectors 2019; 12:499. [PMID: 31647019 PMCID: PMC6813092 DOI: 10.1186/s13071-019-3749-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 10/11/2019] [Indexed: 08/21/2023] Open
Abstract
Background Schistosomiasis is a neglected tropical disease, targeted by the World Health Organization for reduction in morbidity by 2020. It is caused by parasitic flukes that spread through contamination of local water sources. Traditional control focuses on mass drug administration, which kills the majority of adult worms, targeted at school-aged children. However, these drugs do not confer long-term protection and there are concerns over the emergence of drug resistance. The development of a vaccine against schistosomiasis opens the potential for control methods that could generate long-lasting population-level immunity if they are cost-effective. Methods Using an individual-based transmission model, matched to epidemiological data, we compared the cost-effectiveness of a range of vaccination programmes against mass drug administration, across three transmission settings. Health benefit was measured by calculating the heavy-intensity infection years averted by each intervention, while vaccine costs were assessed against robust estimates for the costs of mass drug administration obtained from data. We also calculated a critical vaccination cost, a cost beyond which vaccination might not be economically favorable, by benchmarking the cost-effectiveness of potential vaccines against the cost-effectiveness of mass drug administration, and examined the effect of different vaccine protection durations. Results We found that sufficiently low-priced vaccines can be more cost-effective than traditional drugs in high prevalence settings, and can lead to a greater reduction in morbidity over shorter time-scales. MDA or vaccination programmes that target the whole community generate the most health benefits, but are generally less cost-effective than those targeting children, due to lower prevalence of schistosomiasis in adults. Conclusions The ultimate cost-effectiveness of vaccination will be highly dependent on multiple vaccine characteristics, such as the efficacy, cost, safety and duration of protection, as well as the subset of population targeted for vaccination. However, our results indicate that if a vaccine could be developed with reasonable characteristics and for a sufficiently low cost, then vaccination programmes can be a highly cost-effective method of controlling schistosomiasis in high-transmission areas. The population-level immunity generated by vaccination will also inevitably improve the chances of interrupting transmission of the disease, which is the long-term epidemiological goal.
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Affiliation(s)
- Benjamin S Collyer
- Zeeman Institute (SBIDER), Mathematics Institute, University of Warwick, Coventry, UK.
| | - Hugo C Turner
- Oxford University Clinical Research Unit, Wellcome Trust Overseas Programme, Ho Chi Minh City, Vietnam.,Centre for Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - T Déirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, UK
| | - Matt J Keeling
- Zeeman Institute (SBIDER), Mathematics Institute, University of Warwick, Coventry, UK.,School of Life Sciences, University of Warwick, Coventry, UK
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32
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Toor J, Truscott JE, Werkman M, Turner HC, Phillips AE, King CH, Medley GF, Anderson RM. Determining post-treatment surveillance criteria for predicting the elimination of Schistosoma mansoni transmission. Parasit Vectors 2019; 12:437. [PMID: 31522690 PMCID: PMC6745786 DOI: 10.1186/s13071-019-3611-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 07/08/2019] [Indexed: 01/11/2023] Open
Abstract
Background The World Health Organization (WHO) has set elimination (interruption of transmission) as an end goal for schistosomiasis. However, there is currently little guidance on the monitoring and evaluation strategy required once very low prevalence levels have been reached to determine whether elimination or resurgence of the disease will occur after stopping mass drug administration (MDA) treatment. Methods We employ a stochastic individual-based model of Schistosoma mansoni transmission and MDA impact to determine a prevalence threshold, i.e. prevalence of infection, which can be used to determine whether elimination or resurgence will occur after stopping treatment with a given probability. Simulations are run for treatment programmes with varying probabilities of achieving elimination and for settings where adults harbour low to high burdens of infection. Prevalence is measured based on using a single Kato-Katz on two samples per individual. We calculate positive predictive values (PPV) using PPV ≥ 0.9 as a reliable measure corresponding to ≥ 90% certainty of elimination. We analyse when post-treatment surveillance should be carried out to predict elimination. We also determine the number of individuals across a single community (of 500–1000 individuals) that should be sampled to predict elimination. Results We find that a prevalence threshold of 1% by single Kato-Katz on two samples per individual is optimal for predicting elimination at two years (or later) after the last round of MDA using a sample size of 200 individuals across the entire community (from all ages). This holds regardless of whether the adults have a low or high burden of infection relative to school-aged children. Conclusions Using a prevalence threshold of 0.5% is sufficient for surveillance six months after the last round of MDA. However, as such a low prevalence can be difficult to measure in the field using Kato-Katz, we recommend using 1% two years after the last round of MDA. Higher prevalence thresholds of 2% or 5% can be used but require waiting over four years for post-treatment surveillance. Although, for treatment programmes where elimination is highly likely, these higher thresholds could be used sooner. Additionally, switching to more sensitive diagnostic techniques, will allow for a higher prevalence threshold to be employed. Electronic supplementary material The online version of this article (10.1186/s13071-019-3611-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Jaspreet Toor
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK. .,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.
| | - James E Truscott
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD, UK
| | - Marleen Werkman
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD, UK
| | - Hugo C Turner
- Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Programme, Ho Chi Minh City, Vietnam.,Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Anna E Phillips
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - Charles H King
- Center for Global Health and Diseases and Department of Mathematics, Case Western Reserve University, 10900 Euclid Avenue LC: 4983, Cleveland, OH, 44106, USA
| | - Graham F Medley
- Centre for Mathematical Modelling of Infectious Disease, London School of Hygiene and Tropical Medicine, London, UK
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD, UK
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33
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Truscott JE, Ower AK, Werkman M, Halliday K, Oswald WE, Gichuki PM, Mcharo C, Brooker S, Njenga SM, Mwandariwo C, Walson JL, Pullan R, Anderson R. Heterogeneity in transmission parameters of hookworm infection within the baseline data from the TUMIKIA study in Kenya. Parasit Vectors 2019; 12:442. [PMID: 31522687 PMCID: PMC6745791 DOI: 10.1186/s13071-019-3686-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 08/26/2019] [Indexed: 05/30/2023] Open
Abstract
Background As many countries with endemic soil-transmitted helminth (STH) burdens achieve high coverage levels of mass drug administration (MDA) to treat school-aged and pre-school-aged children, understanding the detailed effects of MDA on the epidemiology of STH infections is desirable in formulating future policies for morbidity and/or transmission control. Prevalence and mean intensity of infection are characterized by heterogeneity across a region, leading to uncertainty in the impact of MDA strategies. In this paper, we analyze this heterogeneity in terms of factors that govern the transmission dynamics of the parasite in the host population. Results Using data from the TUMIKIA study in Kenya (cluster STH prevalence range at baseline: 0–63%), we estimated these parameters and their variability across 120 population clusters in the study region, using a simple parasite transmission model and Gibbs-sampling Monte Carlo Markov chain techniques. We observed great heterogeneity in R0 values, with estimates ranging from 1.23 to 3.27, while k-values (which vary inversely with the degree of parasite aggregation within the human host population) range from 0.007 to 0.29 in a positive association with increasing prevalence. The main finding of this study is the increasing trend for greater parasite aggregation as prevalence declines to low levels, reflected in the low values of the negative binomial parameter k in clusters with low hookworm prevalence. Localized climatic and socioeconomic factors are investigated as potential drivers of these observed epidemiological patterns. Conclusions Our results show that lower prevalence is associated with higher degrees of aggregation and hence prevalence alone is not a good indicator of transmission intensity. As a consequence, approaches to MDA and monitoring and evaluation of community infection status may need to be adapted as transmission elimination is aimed for by targeted treatment approaches.
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Affiliation(s)
- James E Truscott
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Campus, London, W2 1PG, UK. .,MRC Centre for Global Infectious Disease Analysis, Imperial College London, St Mary's Campus, London, W2 1PG, UK. .,The DeWorm3 Project, The Natural History Museum, London, SW7 5BD, UK.
| | - Alison K Ower
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Campus, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Imperial College London, St Mary's Campus, London, W2 1PG, UK
| | - Marleen Werkman
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Campus, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Imperial College London, St Mary's Campus, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum, London, SW7 5BD, UK
| | - Katherine Halliday
- The DeWorm3 Project, The Natural History Museum, London, SW7 5BD, UK.,Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
| | - William E Oswald
- The DeWorm3 Project, The Natural History Museum, London, SW7 5BD, UK.,Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
| | - Paul M Gichuki
- Eastern & Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
| | - Carlos Mcharo
- Eastern & Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
| | | | - Sammy M Njenga
- Eastern & Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
| | - Charles Mwandariwo
- Eastern & Southern Africa Centre of International Parasite Control (ESACIPAC), Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
| | - Judd L Walson
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Campus, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum, London, SW7 5BD, UK.,Departments of Global Health, Medicine (Infectious Disease), Pediatrics and Epidemiology, University of Washington, Seattle, USA
| | - Rachel Pullan
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
| | - Roy Anderson
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Campus, London, W2 1PG, UK.,MRC Centre for Global Infectious Disease Analysis, Imperial College London, St Mary's Campus, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum, London, SW7 5BD, UK
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Majid MF, Kang SJ, Hotez PJ. Resolving "worm wars": An extended comparison review of findings from key economics and epidemiological studies. PLoS Negl Trop Dis 2019; 13:e0006940. [PMID: 30845181 PMCID: PMC6405048 DOI: 10.1371/journal.pntd.0006940] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Muhammad Farhan Majid
- Center for Health and Biosciences, James A Baker III Institute for Public Policy, Rice University, Houston, Texas, United States of America
| | - Su Jin Kang
- Center for Health and Biosciences, James A Baker III Institute for Public Policy, Rice University, Houston, Texas, United States of America
| | - Peter J. Hotez
- Center for Health and Biosciences, James A Baker III Institute for Public Policy, Rice University, Houston, Texas, United States of America
- Department of Pediatrics, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Biology, Baylor University, Waco, Texas, United States of America
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How to eliminate taeniasis/cysticercosis: porcine vaccination and human chemotherapy (Part 2). Theor Biol Med Model 2019; 16:4. [PMID: 30803437 PMCID: PMC6390339 DOI: 10.1186/s12976-019-0100-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 01/29/2019] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND The application of effective vaccines against pig cysticercosis and mass chemotherapy against pig cysticercosis and human taeniasis have shown the feasibility of interrupting the parasite's life cycle in endemic areas. METHODS A mathematical model that divides the population into susceptible, infected, and vaccinated individuals is formulated. The model is based upon the life cycle of the parasite. Computer numerical simulation experiments to evaluate the impact of pig vaccination under different vaccination schedules, and combined intervention strategies including pig vaccination and anthelmintic treatment against human taeniasis are carried out. RESULTS Vaccination against either pig cysticercosis or against human taeniasis will influence the transmission dynamics not only among vaccinees but also the dynamics of the other hosts as well. When the protective efficacy and/or the coverage rate is less than 100%, different mass interventions like vaccinating the pig population twice in combination with chemotherapeutic treatment against human taeniasis, the elimination of the infection in both pigs and humans can also be achieved. CONCLUSIONS Our mathematical model has the potential for planning, and designing effective intervention strategies including both mass vaccination and/or chemotherapeutic treatment to eliminate pig cysticercosis, human taeniasis and human neurocysticercosis. The model can be adapted to any given community with mild, moderate endemicity, or even in hyperendemic regions.
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José MV, Bobadilla JR, Sánchez-Torres NY, Laclette JP. Mathematical model of the life cycle of taenia-cysticercosis: transmission dynamics and chemotherapy (Part 1). Theor Biol Med Model 2018; 15:18. [PMID: 30449280 PMCID: PMC6241031 DOI: 10.1186/s12976-018-0090-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 09/11/2018] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Taenia solium is the aetiological agent of human taeniasis, pig cysticercosis and human neurocysticercosis, which are serious public health problems, especially in developing countries. METHODS A mathematical model of the transmission dynamics of taeniasis-cysticercosis is formulated. The model consists of a coupled system of differential equations, which are density-dependent equations for describing the flow of the parasite through the life cycle. The model is hybrid since it comprises deterministic equations with stochastic elements which describe changes in the mean parasite burden and incorporates the overall pattern of the parasites' distribution. RESULTS Sensitivity and bifurcation analyses were carried out to determine the range of values of the model. The model can reproduce the observed epidemiological patterns of human taeniasis, pig and human cysticercosis. For example, for a wide range of parameter values, the mean intensity of adult worms tends to rapidly stabilize in one parasite per individual host. From this model, we also derived a Susceptible-Infected model to describe the prevalence of infection in humans and pigs. Chemotherapeutic interventions against pig cysticercosis or human taeniasis may reduce rapidly and effectively the mean intensity of human taeniasis, pig cysticercosis and human cysticercosis. This effect can be achieved even if the protective efficacy of the drug is of the order of 90% and the coverage rate is 90%. This means that health in humans infected either with adult worms or cysticerci may be achieved by the application of anthelmintic drugs against pig cysticercosis. However, treatment against human cysticercosis alone, does not influence neither human teniasis nor pig cysticercosis. This is because human cysticercosis infection does not influence the value of the basic reproductive number (Ro). CONCLUSIONS Even coverage of 100% in the administration of anthelmintics did not eliminate the infection. Then elimination of the infection in all hosts does not seem a feasible goal to achieve by administering only chemotherapeutic interventions. Throughout the manuscript a discussion of our model in the context of other models of taeniasis-cysticercosis is presented.
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Affiliation(s)
- Marco V. José
- Theoretical Biology Group, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 CDMX, Mexico
| | - Juan R. Bobadilla
- Theoretical Biology Group, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 CDMX, Mexico
| | - Norma Y. Sánchez-Torres
- Theoretical Biology Group, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 CDMX, Mexico
| | - Juan Pedro Laclette
- Department of Immunology, Biomedical Research Institute, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 CDMX, Mexico
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Toor J, Turner HC, Truscott JE, Werkman M, Phillips AE, Alsallaq R, Medley GF, King CH, Anderson RM. The design of schistosomiasis monitoring and evaluation programmes: The importance of collecting adult data to inform treatment strategies for Schistosoma mansoni. PLoS Negl Trop Dis 2018; 12:e0006717. [PMID: 30296257 PMCID: PMC6175503 DOI: 10.1371/journal.pntd.0006717] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 07/24/2018] [Indexed: 12/02/2022] Open
Abstract
Monitoring and evaluation (M&E) programmes are used to collect data which are required to assess the impact of current interventions on their progress towards achieving the World Health Organization (WHO) goals of morbidity control and elimination as a public health problem for schistosomiasis. Prevalence and intensity of infection data are typically collected from school-aged children (SAC) as they are relatively easy to sample and are thought to be most likely to be infected by schistosome parasites. However, adults are also likely to be infected. We use three different age-intensity profiles of infection for Schistosoma mansoni with low, moderate and high burdens of infection in adults to investigate how the age distribution of infection impacts the mathematical model generated recommendations of the preventive chemotherapy coverage levels required to achieve the WHO goals. We find that for moderate prevalence regions, regardless of the burden of infection in adults, treating SAC only may achieve the WHO goals. However, for high prevalence regions with a high burden of infection in adults, adult treatment is required to meet the WHO goals. Hence, we show that the optimal treatment strategy for a defined region requires consideration of the burden of infection in adults as it cannot be based solely on the prevalence of infection in SAC. Although past epidemiological data have informed mathematical models for the transmission and control of schistosome infections, more accurate and detailed data are required from M&E programmes to accurately determine the optimal treatment strategy for a defined region. We highlight the importance of collecting prevalence and intensity of infection data from a broader age-range, specifically the inclusion of adult data at baseline (prior to treatment) and throughout the treatment programme if possible, rather than SAC only, to accurately determine the treatment strategy for a defined region. Furthermore, we discuss additional epidemiological data, such as individual longitudinal adherence to treatment, that should ideally be collected in M&E programmes. Schistosomiasis remains an endemic parasitic disease affecting millions of people around the world. The World Health Organization (WHO) has set goals of morbidity control and elimination as a public health problem for schistosomiasis defined by reaching ≤5% and ≤1% prevalence of heavy-intensity infections in school-aged children, respectively. Monitoring and evaluation (M&E) programmes are used to collect data which can inform treatment strategies required in a defined area and can also aid in assessing the progress of implemented treatment strategies. Due to programmatic and financial constraints, M&E data are typically collected from school-aged children as they are thought to be most likely to be infected. We highlight that adults should be included within M&E programmes by showing how the burden of infection in adults impacts our mathematical model recommendations of the treatment coverage levels required to reach the WHO goals for schistosomiasis. Our results highlight the importance of collecting data from a broader age-range, specifically the inclusion of adult data at baseline (prior to treatment) and throughout the treatment programme if possible. Improving M&E programmes to incorporate collection of such data will allow for more accurate determination of the optimal treatment strategy for a defined region.
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Affiliation(s)
- Jaspreet Toor
- London Centre for Neglected Tropical Disease Research and Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- * E-mail:
| | - Hugo C. Turner
- Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Programme, Ho Chi Minh City, Vietnam
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - James E. Truscott
- London Centre for Neglected Tropical Disease Research and Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, United Kingdom
| | - Marleen Werkman
- London Centre for Neglected Tropical Disease Research and Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, United Kingdom
| | - Anna E. Phillips
- London Centre for Neglected Tropical Disease Research and Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
| | - Ramzi Alsallaq
- Center for Global Health and Diseases and Department of Mathematics, Case Western Reserve University, Cleveland, Ohio, United States of America
| | - Graham F. Medley
- Centre for Mathematical Modelling of Infectious Disease, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Charles H. King
- Center for Global Health and Diseases and Department of Mathematics, Case Western Reserve University, Cleveland, Ohio, United States of America
| | - Roy M. Anderson
- London Centre for Neglected Tropical Disease Research and Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, St Mary’s Campus, Imperial College London, London, United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, United Kingdom
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Coffeng LE, Truscott JE, Farrell SH, Turner HC, Sarkar R, Kang G, de Vlas SJ, Anderson RM. Comparison and validation of two mathematical models for the impact of mass drug administration on Ascaris lumbricoides and hookworm infection. Epidemics 2018; 18:38-47. [PMID: 28279454 PMCID: PMC5340859 DOI: 10.1016/j.epidem.2017.02.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 01/31/2017] [Accepted: 02/01/2017] [Indexed: 11/02/2022] Open
Abstract
The predictions of two mathematical models of the transmission dynamics of Ascaris lumbricoides and hookworm infection and the impact of mass drug administration (MDA) are compared, using data from India. One model has an age structured partial differential equation (PDE) deterministic framework for the distribution of parasite numbers per host and sexual mating. The second model is an individual-based stochastic model. Baseline data acquired prior to treatment are used to estimate key transmission parameters, and forward projections are made, given the known MDA population coverage. Predictions are compared with observed post-treatment epidemiological patterns. The two models could equally well predict the short-term impact of deworming on A. lumbricoides and hookworm infection levels, despite being fitted to different subsets and/or summary statistics of the data. As such, the outcomes give confidence in their use as aids to policy formulation for the use of PCT to control A. lumbricoides and hookworm infection. The models further largely agree in a qualitative sense on the added benefit of semi-annual vs. annual deworming and targeting of the entire population vs. only children, as well as the potential for interruption of transmission. Further, this study also illustrates that long-term predictions are sensitive to modelling assumptions about which age groups contribute most to transmission, which depends on human demography and age-patterns in exposure and contribution to the environmental reservoir of infection, the latter being notoriously difficult to empirically quantify.
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Affiliation(s)
- Luc E Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands.
| | - James E Truscott
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1 PG, United Kingdom
| | - Sam H Farrell
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1 PG, United Kingdom
| | - Hugo C Turner
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1 PG, United Kingdom
| | - Rajiv Sarkar
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore 632004, Tamil Nadu, India
| | - Gagandeep Kang
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore 632004, Tamil Nadu, India
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St. Mary's Campus, Imperial College London, London WC2 1 PG, United Kingdom
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Kearns PKA, Casey HA, Leach JP. Hypothesis: Multiple sclerosis is caused by three-hits, strictly in order, in genetically susceptible persons. Mult Scler Relat Disord 2018; 24:157-174. [PMID: 30015080 DOI: 10.1016/j.msard.2018.06.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 05/25/2018] [Accepted: 06/18/2018] [Indexed: 12/15/2022]
Abstract
Multiple Sclerosis is a chronic, progressive and debilitating neurological disease which, despite extensive study for over 100 years, remains of enigmatic aetiology. Drawn from the epidemiological evidence, there exists a consensus that there are environmental (possibly infectious) factors that contribute to disease pathogenesis that have not yet been fully elucidated. Here we propose a three-tiered hypothesis: 1) a clinic-epidemiological model of multiple sclerosis as a rare late complication of two sequential infections (with the temporal sequence of infections being important); 2) a proposal that the first event is helminthic infection with Enterobius Vermicularis, and the second is Epstein Barr Virus infection; and 3) a proposal for a testable biological mechanism, involving T-Cell exhaustion for Epstein-Barr Virus protein LMP2A. We believe that this model satisfies some of the as-yet unexplained features of multiple sclerosis epidemiology, is consistent with the clinical and neuropathological features of the disease and is potentially testable by experiment. This model may be generalizable to other autoimmune diseases.
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Warburton EM, Vonhof MJ. From individual heterogeneity to population-level overdispersion: quantifying the relative roles of host exposure and parasite establishment in driving aggregated helminth distributions. Int J Parasitol 2018; 48:309-318. [DOI: 10.1016/j.ijpara.2017.10.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Revised: 10/17/2017] [Accepted: 10/21/2017] [Indexed: 01/25/2023]
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New Perspectives in Equine Intestinal Parasitic Disease: Insights in Monitoring Helminth Infections. Vet Clin North Am Equine Pract 2018; 34:141-153. [PMID: 29426708 DOI: 10.1016/j.cveq.2017.11.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Regular anthelmintic treatment has contributed to anthelmintic resistance in horse helminths. This mass anthelmintic treatment was originally developed owing to a lack of larvicidal drugs against Strongylus vulgaris. The high prevalence of anthelmintic resistance and shortening of strongyle egg reappearance period after avermectins/moxidectins requires epidemiologically appropriate and sustainable measures. Selective anthelmintic treatment is a much-needed deworming approach: More than 50% of adult horses manifest no strongyle egg excretion. In this article, selective anthelmintic treatment procedure is described, with the specific focus on the advantages of an evidence-based, medically appropriate, and sustainable treatment system that slows the development of anthelmintic resistance.
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42
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Johnson PTJ, Wilber MQ. Biological and statistical processes jointly drive population aggregation: using host-parasite interactions to understand Taylor's power law. Proc Biol Sci 2018; 284:rspb.2017.1388. [PMID: 28931738 DOI: 10.1098/rspb.2017.1388] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 08/10/2017] [Indexed: 12/25/2022] Open
Abstract
The macroecological pattern known as Taylor's power law (TPL) represents the pervasive tendency of the variance in population density to increase as a power function of the mean. Despite empirical illustrations in systems ranging from viruses to vertebrates, the biological significance of this relationship continues to be debated. Here we combined collection of a unique dataset involving 11 987 amphibian hosts and 332 684 trematode parasites with experimental measurements of core epidemiological outcomes to explicitly test the contributions of hypothesized biological processes in driving aggregation. After using feasible set theory to account for mechanisms acting indirectly on aggregation and statistical constraints inherent to the data, we detected strongly consistent influences of host and parasite species identity over 7 years of sampling. Incorporation of field-based measurements of host body size, its variance and spatial heterogeneity in host density accounted for host identity effects, while experimental quantification of infection competence (and especially virulence from the 20 most common host-parasite combinations) revealed the role of species-by-environment interactions. By uniting constraint-based theory, controlled experiments and community-based field surveys, we illustrate the joint influences of biological and statistical processes on parasite aggregation and emphasize their importance for understanding population regulation and ecological stability across a range of systems, both infectious and free-living.
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Affiliation(s)
- Pieter T J Johnson
- Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA
| | - Mark Q Wilber
- Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, 93106, USA
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Abstract
Together, malaria and the neglected tropical diseases (NTDs) kill more than 800,000 people annually, while creating long-term disability in millions more. International support for mass drug administration, bed nets, and other preventive measures has resulted in huge public health gains, while support for translational research is leading to the development of some new neglected disease drugs, diagnostics, and vaccines. However, funding for basic science research has not kept up, such that we are missing opportunities to create a more innovative pipeline of control tools for parasitic and related diseases. There is an urgent need to expand basic science approaches for neglected diseases, especially in the areas of systems biology and immunology; ecology, evolution, and mathematical biology; functional and comparative OMICs; gene editing; expanded use of model organisms; and a new single-cell combinatorial indexing RNA sequencing approach. The world’s poor deserve access to innovation for neglected diseases. It should be considered a fundamental human right.
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Affiliation(s)
- Peter J. Hotez
- Texas Children’s Hospital Center for Vaccine Development, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Biology, Baylor University, Waco, Texas, United States of America
- * E-mail:
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Knubben-Schweizer G, Pfister K. [Anthelmintic resistance in ruminants: development, diagnostics, and procedures]. Tierarztl Prax Ausg G Grosstiere Nutztiere 2017; 45:244-251. [PMID: 28765867 DOI: 10.15653/tpg-170287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 07/14/2017] [Indexed: 11/22/2022]
Abstract
Anthelmintic resistance of gastrointestinal nematodes in small ruminants, but also in cattle and horses, is now found worldwide. The reason for increasing anthelmintic resistance is, in particular, the extensive use of all the anthelmintic agents available on the market. A non-targeted use leads to the selection of naturally occurring resistance genes within parasite populations. The most practical method for evaluating the efficacy of an anthelmintic is the fecal egg-count reduction test. To reduce the rate of anthelmintic resistance development, the available active substances must be applied less and in a targeted manner. When applying targeted (selective) treatment, part of the herd is left untreated. Therefore, it is necessary to identify the animals that require treatment for health or economic reasons. To decide on anthelmintic treatment, findings can be collected from single animals or from a group of animals in a herd. To determine which groups of animals are to be treated within a herd (targeted treatment), pooled fecal samples (cattle and small ruminants), serum pepsinogen concentration (cattle), or Ostertagia ostertagi antibodies in the bulk milk (cattle) can be analyzed. For individual animal (targeted selective) treatment, criteria including fecal egg count (cattle and small ruminants), conjuctival color as an indicator for infection with Haemonchus contortus (FAMACHA®, small ruminants), body condition in adult animals (small ruminants), weight gain in juvenile animals (cattle and small ruminants), and the consistency of the feces (small ruminants) are used. These decision criteria can also be combined to enhance the informative value. Furthermore, an efficacy test of the anthelmintics used should be performed regularly at the beginning of the pasture season. During the pasture season, a low infection pressure should be maintained by pasture management strategies. The goal of sustainable parasite management is the reduction of anthelmintic treatment while maintaining the productivity and health of the animals and thus a longer effectiveness of the available drugs.
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Affiliation(s)
- Gabriela Knubben-Schweizer
- Prof. Dr. Gabriela Knubben-Schweizer, Klinik für Wiederkäuer mit Ambulanz und Bestandsbetreuung, Tierärztliche Fakultät der LMU München, Sonnenstraße 16, 85764 Oberschleißheim, E-Mail:
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Stylianou A, Hadjichrysanthou C, Truscott JE, Anderson RM. Developing a mathematical model for the evaluation of the potential impact of a partially efficacious vaccine on the transmission dynamics of Schistosoma mansoni in human communities. Parasit Vectors 2017; 10:294. [PMID: 28623957 PMCID: PMC5474049 DOI: 10.1186/s13071-017-2227-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 06/01/2017] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND There is currently no vaccine available to protect humans against infection with the schistosome digenean parasites, although candidate formulations for Schistosoma mansoni are under trial in animal models, including rodents and primates. Current strategies for the control of infection are based on mass drug administration (MDA) targeted at school-aged children of age 5 to 14 years. This approach is unlikely to eliminate exposure to infection except in settings with very low levels of transmission. METHODS A deterministic mathematical model for the transmission dynamics of the parasite is described and employed to investigate community level outcomes. The model is defined to encompass two different delivery strategies for the vaccination of the population, namely, infant (cohort) and mass vaccination. However, in this paper the focus is on vaccination delivered in a cohort immunisation programme where infants are immunised within the first year of life before acquiring infection. An analysis of the parasite's transmission dynamics following the administration of a partially protective vaccine is presented. The vaccine acts on parasite mortality, fecundity or/and establishment. RESULTS A vaccine with an efficacy of over 60% can interrupt transmission in low and moderate transmission settings. In higher transmission intensity areas, greater efficacy or higher infant vaccination coverage is required. Candidate vaccines that act either on parasite mortality, fecundity or establishment within the human host, can be similarly effective. In all cases, however, the duration of protection is important. The community level impact of vaccines with all modes of action, declines if vaccine protection is of a very short duration. However, durations of protection of 5-10 years or more are sufficient, with high coverage and efficacy levels, to halt transmission. The time taken to break transmission may be 18 years or more after the start of the cohort vaccination, depending on the intensity of the transmission in a defined location. CONCLUSIONS The analyses provide support for the proposition that even a partially efficacious vaccine could be of great value in reducing the burden of schistosome infections in endemic regions and hopefully could provide a template for the elimination of parasite transmission.
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Affiliation(s)
- Andria Stylianou
- London Centre for Neglected Tropical Disease Research, London, UK
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, London, UK
| | - Christoforos Hadjichrysanthou
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, London, UK
| | - James E. Truscott
- London Centre for Neglected Tropical Disease Research, London, UK
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, London, UK
| | - Roy M. Anderson
- London Centre for Neglected Tropical Disease Research, London, UK
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, London, UK
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Farrell SH, Truscott JE, Anderson RM. The importance of patient compliance in repeated rounds of mass drug administration (MDA) for the elimination of intestinal helminth transmission. Parasit Vectors 2017; 10:291. [PMID: 28606164 PMCID: PMC5469187 DOI: 10.1186/s13071-017-2206-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 05/17/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Systematic non-compliance to chemotherapeutic treatment among a portion of the eligible population is thought to be a major obstacle to the elimination of helminth infections by mass drug administration (MDA). MDA for helminths is repeated at defined intervals such as yearly or every 2 years, as a consequence of the inability of the human host to develop fully protective immunity to reinfection. As such, how an individual complies to these repeated rounds of MDA can have a significant impact on parasite transmission. The importance of this factor is poorly understood at present. Few epidemiological studies have examined longitudinal trends in compliance in the many communities in areas of endemic helminth infection that are undergoing MDA. Reducing systematic non-compliance will obviously increase the number of individuals treated, but it may also alter the dynamics of parasite transmission. METHODS Here we develop an individual-based stochastic model of helminth transmission and MDA treatment to investigate how different patterns of compliance influence the impact of MDA for two groups of helminths, the soil transmitted nematode infections and the schistosome parasites. We study the effect of several alternative treatment and compliance patterns on the dynamics of transmission. RESULTS We find that the impact of different compliance patterns, ranging from random treatment at each round of chemotherapy to systematic non-compliance by a proportion of the population, is very dependent on both transmission intensity in a defined setting and the type of infection that the treatment is targeted at. Systematic non-compliance has a greater impact on the potential for elimination of Schistosoma mansoni transmission by intensive MDA, than it does on Ascaris lumbricoides. CONCLUSIONS We discuss the implications of our findings for the prioritisation of resources in MDA programmes and for monitoring and evaluation programme design. The key message generated by the analyses is that great care must be taken to record individual longitudinal patterns of compliance at each round of MDA as opposed to just recording overall coverage.
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Affiliation(s)
- Sam H Farrell
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, London, W2 1PG, UK.
| | - James E Truscott
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, London, W2 1PG, UK.,The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD, UK
| | - Roy M Anderson
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, St Mary's Campus, Imperial College London, London, W2 1PG, UK
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Werkman M, Truscott JE, Toor J, Wright JE, Anderson RM. The past matters: estimating intrinsic hookworm transmission intensity in areas with past mass drug administration to control lymphatic filariasis. Parasit Vectors 2017; 10:254. [PMID: 28535806 PMCID: PMC5493118 DOI: 10.1186/s13071-017-2177-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Accepted: 05/05/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Current WHO guidelines for soil-transmitted helminth (STH) control focus on mass drug administration (MDA) targeting preschool-aged (pre-SAC) and school-aged children (SAC), with the goal of eliminating STH as a public health problem amongst children. Recently, attention and funding has turned towards the question whether MDA alone can result in the interruption of transmission for STH. The lymphatic filariasis (LF) elimination programme, have been successful in reaching whole communities. There is the possibility of building upon the infrastructure created for these LF-programmes to enhance the control of STH. Using hookworm as an example, we explore what further MDA coverage might be required to induce interruption of transmission for hookworm in the wake of a successful LF programme. RESULTS Analyses based on the model of STH transmission and MDA impact predict the effects of previous LF control by MDA over five years, on a defined baseline prevalence of STH in an area with a defined transmission intensity (the basic reproductive number R0). If the LF MDA programme achieved a high coverage (70, 70 and 60% for pre-SAC, SAC and adults, respectively) we expect that in communities with a hookworm prevalence of 15%, after 5 years of LF control, the intrinsic R0 value in that setting is 2.47. By contrast, if lower LF coverages were achieved (40, 40 and 30% for pre-SAC, SAC and adults, respectively), with the same prevalence of 15% at baseline (after 5 years of LF MDA), the intrinsic hookworm R0 value is predicted to be 1.67. The intrinsic R0 value has a large effect on the expected successes of follow-up STH programmes post LF MDA. Consequently, the outcomes of identical programmes may differ between these communities. CONCLUSION To design the optimal MDA intervention to eliminate STH infections, it is vital to have information on historical MDA programmes and baseline prevalence to estimate the intrinsic transmission intensity for the defined setting (R0). The baseline prevalence alone is not sufficient to inform policy for the control of STH, post cessation of LF MDA, since this will be highly dependent on the intensity and effectiveness of past programmes and the intrinsic transmission intensity of the dominant STH species in any given setting.
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Affiliation(s)
- Marleen Werkman
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary’s Campus, Imperial College London, London, W2 1PG United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD United Kingdom
| | - James E. Truscott
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary’s Campus, Imperial College London, London, W2 1PG United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD United Kingdom
| | - Jaspreet Toor
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary’s Campus, Imperial College London, London, W2 1PG United Kingdom
| | - James E. Wright
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary’s Campus, Imperial College London, London, W2 1PG United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD United Kingdom
| | - Roy M. Anderson
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, St. Mary’s Campus, Imperial College London, London, W2 1PG United Kingdom
- The DeWorm3 Project, The Natural History Museum of London, London, SW7 5BD United Kingdom
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Campbell SJ, Nery SV, Wardell R, D’Este CA, Gray DJ, McCarthy JS, Traub RJ, Andrews RM, Llewellyn S, Vallely AJ, Williams GM, Clements ACA. Water, Sanitation and Hygiene (WASH) and environmental risk factors for soil-transmitted helminth intensity of infection in Timor-Leste, using real time PCR. PLoS Negl Trop Dis 2017; 11:e0005393. [PMID: 28346536 PMCID: PMC5383321 DOI: 10.1371/journal.pntd.0005393] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 04/06/2017] [Accepted: 02/06/2017] [Indexed: 11/18/2022] Open
Abstract
Background No investigations have been undertaken of risk factors for intensity of soil-transmitted helminth (STH) infection in Timor-Leste. This study provides the first analysis of risk factors for intensity of STH infection, as determined by quantitative PCR (qPCR), examining a broad range of water, sanitation and hygiene (WASH) and environmental factors, among communities in Manufahi District, Timor-Leste. Methods A baseline cross-sectional survey of 18 communities was undertaken as part of a cluster randomised controlled trial, with additional identically-collected data from six other communities. qPCR was used to assess STH infection from stool samples, and questionnaires administered to collect WASH, demographic, and socioeconomic data. Environmental information was obtained from open-access sources and linked to infection outcomes. Mixed-effects multinomial logistic regression was undertaken to assess risk factors for intensity of Necator americanus and Ascaris infection. Results 2152 participants provided stool and questionnaire information for this analysis. In adjusted models incorporating WASH, demographic and environmental variables, environmental variables were generally associated with infection intensity for both N. americanus and Ascaris spp. Precipitation (in centimetres) was associated with increased risk of moderate-intensity (adjusted relative risk [ARR] 6.1; 95% confidence interval [CI] 1.9–19.3) and heavy-intensity (ARR 6.6; 95% CI 3.1–14.1) N. americanus infection, as was sandy-loam soil around households (moderate-intensity ARR 2.1; 95% CI 1.0–4.3; heavy-intensity ARR 2.7; 95% CI 1.6–4.5; compared to no infection). For Ascaris, alkaline soil around the household was associated with reduced risk of moderate-intensity infection (ARR 0.21; 95% CI 0.09–0.51), and heavy-intensity infection (ARR 0.04; 95% CI 0.01–0.25). Few WASH risk factors were significant. Conclusion In this high-prevalence setting, strong risk associations with environmental factors indicate that anthelmintic treatment alone will be insufficient to interrupt STH transmission, as conditions are favourable for ongoing environmental transmission. Integrated STH control strategies should be explored as a priority. We present a detailed analysis of WASH, environmental and demographic factors associated with intensity of STH infection in Manufahi District, Timor-Leste, using qPCR. Investigation of risk factors for intensity of STH infection is rarely undertaken, and prior analyses have used microscopic-based eggs per gram of faeces (epg) measures, which are of lower diagnostic accuracy than qPCR. Additionally, few analyses have investigated combined WASH and environmental risk factors in association with STH. This is important due to the extensive potential interrelatedness of environmental, social, behavioural and host factors in any given setting influencing STH survival and transmission. This analysis uses categorical intensity of infection variables for Necator americanus and Ascaris spp., and advanced statistical modelling to adjust for multinomial intensity outcomes, dependency of observations, effects of poverty, and confounding from other measured variables. As such, this analysis provides a comprehensive assessment of risk factors for STH in Manufahi District, Timor-Leste. This is of importance for development of policy and programmatic decisions; risk factors need to be considered not only for their clinical and statistical significance, but more broadly in terms of what may represent modifiable pathways for STH transmission.
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Affiliation(s)
- Suzy J. Campbell
- Research School of Population Health, College of Medicine, Biology and Environment, The Australian National University, Acton, Australian Capital Territory, Australia
- * E-mail:
| | - Susana V. Nery
- Research School of Population Health, College of Medicine, Biology and Environment, The Australian National University, Acton, Australian Capital Territory, Australia
| | - Rebecca Wardell
- Research School of Population Health, College of Medicine, Biology and Environment, The Australian National University, Acton, Australian Capital Territory, Australia
| | - Catherine A. D’Este
- Research School of Population Health, College of Medicine, Biology and Environment, The Australian National University, Acton, Australian Capital Territory, Australia
| | - Darren J. Gray
- Research School of Population Health, College of Medicine, Biology and Environment, The Australian National University, Acton, Australian Capital Territory, Australia
- Molecular Parasitology Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
- School of Public Health, University of Queensland, Brisbane, Queensland, Australia
| | - James S. McCarthy
- School of Public Health, University of Queensland, Brisbane, Queensland, Australia
- Clinical Tropical Medicine Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
| | - Rebecca J. Traub
- Faculty of Veterinary and Agricultural Science, The University of Melbourne, Parkville, Victoria, Australia
| | - Ross M. Andrews
- Menzies School of Health Research, Charles Darwin University, Casuarina, Northern Territory, Australia
| | - Stacey Llewellyn
- Clinical Tropical Medicine Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
| | - Andrew J. Vallely
- Kirby Institute, University of New South Wales, Wallace Wurth Building, Kensington, New South Wales, Australia
| | - Gail M. Williams
- School of Public Health, University of Queensland, Brisbane, Queensland, Australia
| | - Archie C. A. Clements
- Research School of Population Health, College of Medicine, Biology and Environment, The Australian National University, Acton, Australian Capital Territory, Australia
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49
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Sarkar R, Rose A, Mohan VR, Ajjampur SSR, Veluswamy V, Srinivasan R, Muliyil J, Rajshekhar V, George K, Balraj V, Grassly NC, Anderson RM, Brooker SJ, Kang G. Study design and baseline results of an open-label cluster randomized community-intervention trial to assess the effectiveness of a modified mass deworming program in reducing hookworm infection in a tribal population in southern India. Contemp Clin Trials Commun 2017; 5:49-55. [PMID: 28424794 PMCID: PMC5389336 DOI: 10.1016/j.conctc.2016.12.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Revised: 10/25/2016] [Accepted: 12/03/2016] [Indexed: 11/17/2022] Open
Abstract
Introduction Hookworm infection is a leading cause of iron deficiency anemia and malnutrition in resource-poor settings. Periodic mass deworming with anthelminthic drugs remains the cornerstone of hookworm control efforts worldwide. Reinfection following treatment occurs, reflecting the human host's inability to acquire immunity following exposure to an untreated reservoir of infection. This cluster randomized trial will evaluate the effectiveness of a modified, population-based, mass deworming strategy in reducing hookworm infection in an endemic southern Indian population. Methods Forty five tribal villages were randomized into three groups: one received annual treatment; the second received two rounds of treatment at 1-month intervals; and the third received four rounds of treatment – two rounds 1 month apart at the beginning, followed by another two after 6 months. Stool samples collected through cross-sectional parasitological surveys pre- and post-intervention, and at 3-monthly intervals for a period of 1 year were tested for presence of hookworm ova. Long-term effectiveness of treatment will be assessed through another survey conducted 2 years after the last treatment cycle. Results From a population of 11,857 individuals, 8681 (73.2%) were found to be eligible and consented to participate, out-migration being the primary reason for non-participation. Baseline stool samples were obtained from 2082 participants, with 18.5% having hookworm infection, although majority were low intensity infections (<2000 eggs per gram of feces). Discussion This study will help identify the optimal mass deworming strategy that can achieve the greatest impact in the shortest period of time, particularly in settings where long-term program sustainability is a challenge.
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Affiliation(s)
- Rajiv Sarkar
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
| | - Anuradha Rose
- Community Health Department, Christian Medical College, Vellore, 632002, Tamil Nadu, India
| | - Venkata R Mohan
- Community Health Department, Christian Medical College, Vellore, 632002, Tamil Nadu, India
| | - Sitara S R Ajjampur
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
| | - Vasanthakumar Veluswamy
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
| | - Rajan Srinivasan
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
| | - Jayaprakash Muliyil
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
| | - Vedantam Rajshekhar
- Department of Neurological Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
| | - Kuryan George
- Community Health Department, Christian Medical College, Vellore, 632002, Tamil Nadu, India
| | - Vinohar Balraj
- Society for Applied Studies, No. 14, Natteri Krishnamachari Street, Krishna Nagar, Vellore, 632001, Tamil Nadu, India
| | - Nicholas C Grassly
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, Norfolk Place, London, W2 1NY, United Kingdom
| | - Roy M Anderson
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, Norfolk Place, London, W2 1NY, United Kingdom
| | - Simon J Brooker
- Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, United Kingdom
| | - Gagandeep Kang
- Division of Gastrointestinal Sciences, Christian Medical College, Vellore, 632004, Tamil Nadu, India
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50
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Simoonga C, Kazembe LN. Using the hierarchical ordinal regression model to analyse the intensity of urinary schistosomiasis infection in school children in Lusaka Province, Zambia. Infect Dis Poverty 2017; 6:43. [PMID: 28219411 PMCID: PMC5319044 DOI: 10.1186/s40249-017-0262-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 02/16/2017] [Indexed: 12/19/2022] Open
Abstract
Background Urinary schistosomiasis has been a major public health problem in Zambia for many years. However, the disease profile may vary in different locale due to the changing ecosystem that contributes to the risk of acquiring the disease. The objective of this study was to quantify risk factors associated with the intensity of urinary schistosomiasis infection in school children in Lusaka Province, Zambia, in order to better understand local transmission. Methods Data were obtained from 1 912 school children, in 20 communities, in the districts of Luangwa and Kafue in Lusaka Province. Both individual- and community-level covariates were incorporated into an ordinal logistic regression model to predict the probability of an infection being a certain intensity in a three-category outcome response: 0 = no infection, 1 = light infection, and 2 = moderate/heavy infection. Random effects were introduced to capture unobserved heterogeneity. Results Overall, the risk of urinary schistosomiasis was strongly associated with age, altitude at which the child lived, and sex. Weak associations were observed with the normalized difference vegetation index, maximum temperature, and snail abundance. Detailed analysis indicated that the association between infection intensities and age and altitude were category-specific. Particularly, infection intensity was lower in children aged between 5 and 9 years compared to those aged 10 to 15 years (OR = 0.72, 95% CI = 0.51–0.99). However, the age-specific risk changed at different levels of infection, such that when comparing children with light infection to those who were not infected, age was associated with a lower odds (category 1 vs category 0: OR = 0.71, 95% CI: 0.50–0.99), yet such a relation was not significant when considering children who were moderately or heavily infected compared to those with a light or no infection (category 2 vs category 0: OR = 0.96, 95% CI: 0.45–1.64). Overall, we observed that children living in the valley were less likely to acquire urinary schistosomiasis compared to those living in plateau areas (OR = 0.48, 95% CI: 0.16–0.71). However, category-specific effects showed no significant association in category 1 (light infection), whereas in category 2 (moderate/high infection), the risk was still significantly lower for those living in the valley compared to those living in plateau areas (OR = 0.18, 95% CI: 0.04–0.75). Conclusions This study demonstrates the importance of understanding the dynamics and heterogeneity of infection in control efforts, and further suggests that apart from the well-researched factors of Schistosoma intensity, various other factors influence transmission. Control programmes need to take into consideration the varying infection intensities of the disease so that effective interventions can be designed. Electronic supplementary material The online version of this article (doi:10.1186/s40249-017-0262-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Christopher Simoonga
- Ministry of Health, Ndeke House, Haile Selassie Avenue, P.O. Box 30205, Lusaka, Zambia
| | - Lawrence N Kazembe
- Mathematical Sciences Department, Chancellor College, University of Malawi, P.O. Box 280, Zomba, Malawi. .,Statistics and Population Studies Department, University of Namibia, Private Bag 13301, Windhoek, Namibia.
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