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Antony Oliver MC, Graham M, Gass KM, Medley GF, Clark J, Davis EL, Reimer LJ, King JD, Pouwels KB, Hollingsworth TD. Reducing the Antigen Prevalence Target Threshold for Stopping and Restarting Mass Drug Administration for Lymphatic Filariasis Elimination: A Model-Based Cost-effectiveness Simulation in Tanzania, India and Haiti. Clin Infect Dis 2024; 78:S160-S168. [PMID: 38662697 PMCID: PMC11045020 DOI: 10.1093/cid/ciae108] [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 Global Programme to Eliminate Lymphatic Filariasis (GPELF) aims to reduce and maintain infection levels through mass drug administration (MDA), but there is evidence of ongoing transmission after MDA in areas where Culex mosquitoes are the main transmission vector, suggesting that a more stringent criterion is required for MDA decision making in these settings. METHODS We use a transmission model to investigate how a lower prevalence threshold (<1% antigenemia [Ag] prevalence compared with <2% Ag prevalence) for MDA decision making would affect the probability of local elimination, health outcomes, the number of MDA rounds, including restarts, and program costs associated with MDA and surveys across different scenarios. To determine the cost-effectiveness of switching to a lower threshold, we simulated 65% and 80% MDA coverage of the total population for different willingness to pay per disability-adjusted life-year averted for India ($446.07), Tanzania ($389.83), and Haiti ($219.84). RESULTS Our results suggest that with a lower Ag threshold, there is a small proportion of simulations where extra rounds are required to reach the target, but this also reduces the need to restart MDA later in the program. For 80% coverage, the lower threshold is cost-effective across all baseline prevalences for India, Tanzania, and Haiti. For 65% MDA coverage, the lower threshold is not cost-effective due to additional MDA rounds, although it increases the probability of local elimination. Valuing the benefits of elimination to align with the GPELF goals, we find that a willingness to pay per capita government expenditure of approximately $1000-$4000 for 1% increase in the probability of local elimination would be required to make a lower threshold cost-effective. CONCLUSIONS Lower Ag thresholds for stopping MDAs generally mean a higher probability of local elimination, reducing long-term costs and health impacts. However, they may also lead to an increased number of MDA rounds required to reach the lower threshold and, therefore, increased short-term costs. Collectively, our analyses highlight that lower target Ag thresholds have the potential to assist programs in achieving lymphatic filariasis goals.
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Affiliation(s)
- Mary Chriselda Antony Oliver
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom
| | - Matthew Graham
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom
| | - Katherine M Gass
- Neglected Tropical Diseases Support Centre, The Task Force for Global Health, Decatur, Georgia, USA
| | - Graham F Medley
- Centre for Mathematical Modelling of Infectious Disease and Department of Global Health and Development, London School of Hygiene & Tropical Medicine, London, United Kingdom
| | - Jessica Clark
- School of Biodiversity, One Health and Veterinary Medicine, University of Glasgow, Glasgow, United Kingdom
| | - Emma L Davis
- Mathematics Institute and the Zeeman Institute for Systems Biology and Infectious Disease Epidemiological Research, University of Warwick, Coventry, United Kingdom
| | - Lisa J Reimer
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Jonathan D King
- Department of Control of Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland
| | - Koen B Pouwels
- Health Economics Research Centre, Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
| | - T Déirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom
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Sharma S, Smith ME, Bilal S, Michael E. Evaluating elimination thresholds and stopping criteria for interventions against the vector-borne macroparasitic disease, lymphatic filariasis, using mathematical modelling. Commun Biol 2023; 6:225. [PMID: 36849730 PMCID: PMC9971242 DOI: 10.1038/s42003-022-04391-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Accepted: 12/20/2022] [Indexed: 03/01/2023] Open
Abstract
We leveraged the ability of EPIFIL transmission models fit to field data to evaluate the use of the WHO Transmission Assessment Survey (TAS) for supporting Lymphatic Filariasis (LF) intervention stopping decisions. Our results indicate that understanding the underlying parasite extinction dynamics, particularly the protracted transient dynamics involved in shifts to the extinct state, is crucial for understanding the impacts of using TAS for determining the achievement of LF elimination. These findings warn that employing stopping criteria set for operational purposes, as employed in the TAS strategy, without a full consideration of the dynamics of extinction could seriously undermine the goal of achieving global LF elimination.
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Affiliation(s)
- Swarnali Sharma
- Christian Medical College, IDA Scudder Road, Vellore, Tamil Nadu, 632004, India.
| | - Morgan E Smith
- Department of Biological Sciences, University of Notre Dame, Notre Dame, South Bend, IN, USA
| | - Shakir Bilal
- Center for Global Health Infectious Disease Research, University of South Florida, Tampa, FL, USA
| | - Edwin Michael
- Center for Global Health Infectious Disease Research, University of South Florida, Tampa, FL, USA.
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3
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Larrieu E, Gavidia CM, Lightowlers MW. Control of cystic echinococcosis: Background and prospects. Zoonoses Public Health 2019; 66:889-899. [PMID: 31529690 DOI: 10.1111/zph.12649] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Revised: 08/06/2019] [Accepted: 08/24/2019] [Indexed: 12/14/2022]
Abstract
Cystic echinococcosis (CE), caused by Echinococcus granulosus, is a chronic and debilitating zoonotic larval cestode infection in humans, which is principally transmitted between dogs and domestic livestock, particularly sheep. Human CE occurs in almost all pastoral communities and rangeland areas of the underdeveloped and developed world. Control programmes against CE have been implemented in several endemic countries to reduce or eliminate the disease. New Zealand and Tasmania are examples of some of the first programmes to be undertaken (in insular territories) and which were very successful in the elimination of CE. The advent and proven effectiveness of praziquantel, plus the experience of insular models, produced high expectations for rapid advances in a second generation of control programmes undertaken in continental areas (Argentina, Uruguay and Chile). Nevertheless, only moderate gains in CE control have been made and the impact on prevalence among humans has been slight. A major impediment to the adoption of procedures that were successful in New Zealand and Tasmania has been the requirement to administer praziquantel to dogs in rural areas eight times per year over numerous years. In addition, there have been clear technological improvements made in the diagnosis of canine echinococcosis for surveillance, the genetic characterization of parasite strains and in vaccination against CE infection in livestock. In order to establish new paradigms and appropriate combinations of control strategies, we have carried out a review and discussion of the available control tools and control models. Control strategies must be suitable and sustainable to benefit the Echinococcosis-endemic areas primarily, which at the same time are the poorest regions of the world.
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Affiliation(s)
- Edmundo Larrieu
- Facultad de Veterinaria, Universidad Nacional de La Pampa, General Pico, Argentina.,Escuela de Veterinaria, Universidad Nacional de Rio Negro, Choele Choel, Argentina
| | - Cesar M Gavidia
- Facultad de Medicina Veterinaria, Universidad Nacional Mayor de San Marcos, Lima, Perú
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Arakala A, Hoover CM, Marshall JM, Sokolow SH, De Leo GA, Rohr JR, Remais JV, Gambhir M. Estimating the elimination feasibility in the 'end game' of control efforts for parasites subjected to regular mass drug administration: Methods and their application to schistosomiasis. PLoS Negl Trop Dis 2018; 12:e0006794. [PMID: 30418968 PMCID: PMC6258430 DOI: 10.1371/journal.pntd.0006794] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 11/26/2018] [Accepted: 08/27/2018] [Indexed: 11/18/2022] Open
Abstract
Progress towards controlling and eliminating parasitic worms, including schistosomiasis, onchocerciasis, and lymphatic filariasis, is advancing rapidly as national governments, multinational NGOs, and pharmaceutical companies launch collaborative chemotherapeutic control campaigns. Critical questions remain regarding the potential for achieving elimination of these infections, and analytical methods can help to quickly estimate progress towards-and the probability of achieving-elimination over specific timeframes. Here, we propose the effective reproduction number, Reff, as a proxy of elimination potential for sexually reproducing worms that are subject to poor mating success at very low abundance (positive density dependence, or Allee effects). Reff is the number of parasites produced by a single reproductive parasite at a given stage in the transmission cycle, over the parasite's lifetime-it is the generalized form of the more familiar basic reproduction number, R0, which only applies at the beginning of an epidemic-and it can be estimated in a 'model-free' manner by an estimator ('ε'). We introduce ε, demonstrate its estimation using simulated data, and discuss how it may be used in planning and evaluation of ongoing elimination efforts for a range of parasitic diseases.
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Affiliation(s)
- Arathi Arakala
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia
| | - Christopher M. Hoover
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America
| | - John M. Marshall
- Division of Epidemiology and Biostatistics, School of Public Health, University of California, Berkeley, California, United States of America
| | - Susanne H. Sokolow
- Department of Biology—Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
| | - Giulio A. De Leo
- Department of Biology—Hopkins Marine Station, Stanford University, Pacific Grove, California, United States of America
| | - Jason R. Rohr
- Department of Integrative Biology, University of Southern Florida, Tampa, Florida, United States of America
| | - Justin V. Remais
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California, United States of America
| | - Manoj Gambhir
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia
- Health Modelling and Analytics, IBM Research Australia, Melbourne, Australia
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Michael E, Smith ME, Katabarwa MN, Byamukama E, Griswold E, Habomugisha P, Lakwo T, Tukahebwa E, Miri ES, Eigege A, Ngige E, Unnasch TR, Richards FO. Substantiating freedom from parasitic infection by combining transmission model predictions with disease surveys. Nat Commun 2018; 9:4324. [PMID: 30337529 PMCID: PMC6193962 DOI: 10.1038/s41467-018-06657-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 09/14/2018] [Indexed: 11/22/2022] Open
Abstract
Stopping interventions is a critical decision for parasite elimination programmes. Quantifying the probability that elimination has occurred due to interventions can be facilitated by combining infection status information from parasitological surveys with extinction thresholds predicted by parasite transmission models. Here we demonstrate how the integrated use of these two pieces of information derived from infection monitoring data can be used to develop an analytic framework for guiding the making of defensible decisions to stop interventions. We present a computational tool to perform these probability calculations and demonstrate its practical utility for supporting intervention cessation decisions by applying the framework to infection data from programmes aiming to eliminate onchocerciasis and lymphatic filariasis in Uganda and Nigeria, respectively. We highlight a possible method for validating the results in the field, and discuss further refinements and extensions required to deploy this predictive tool for guiding decision making by programme managers. The decision when to stop an intervention is a critical component of parasite elimination programmes, but reliance on surveillance data alone can be inaccurate. Here, Michael et al. combine parasite transmission model predictions with disease survey data to more reliably determine when interventions can be stopped.
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Affiliation(s)
- Edwin Michael
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, 46556, USA.
| | - Morgan E Smith
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, 46556, USA
| | - Moses N Katabarwa
- Emory University and The Carter Center, One Copenhill, 453 Freedom Parkway, Atlanta, GA, 30307, USA
| | | | - Emily Griswold
- Emory University and The Carter Center, One Copenhill, 453 Freedom Parkway, Atlanta, GA, 30307, USA
| | | | - Thomson Lakwo
- Vector Control Division, Ministry of Health, 15 Bombo Road, P.O. Box 1661, Kampala, Uganda
| | - Edridah Tukahebwa
- Vector Control Division, Ministry of Health, 15 Bombo Road, P.O. Box 1661, Kampala, Uganda
| | - Emmanuel S Miri
- The Carter Center, Nigeria, 1 Jeka Kadima Street off Tudun Wada Ring Road, Jos, Nigeria
| | - Abel Eigege
- The Carter Center, Nigeria, 1 Jeka Kadima Street off Tudun Wada Ring Road, Jos, Nigeria
| | - Evelyn Ngige
- Federal Ministry of Health, Federal Sceretariat, Garki-Abuja, Nigeria
| | - Thomas R Unnasch
- Global Health Infectious Disease Research, College of Public Health, University of South Florida, 33620, Tampa, FL, USA
| | - Frank O Richards
- Emory University and The Carter Center, One Copenhill, 453 Freedom Parkway, Atlanta, GA, 30307, USA
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6
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Walker M, Stolk WA, Dixon MA, Bottomley C, Diawara L, Traoré MO, de Vlas SJ, Basáñez MG. Modelling the elimination of river blindness using long-term epidemiological and programmatic data from Mali and Senegal. Epidemics 2018; 18:4-15. [PMID: 28279455 PMCID: PMC5340858 DOI: 10.1016/j.epidem.2017.02.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2016] [Revised: 02/03/2017] [Accepted: 02/07/2017] [Indexed: 11/11/2022] Open
Abstract
Onchocerciasis is earmarked for elimination in some African countries by 2020/2025. 15+ years of ivermectin treatment drove infection prevalence to zero in areas of Mali & Senegal. Data-driven model projections are used to evaluate the risk of infection resurgence. Latent infections can initiate slow resurgence in communities with high transmission propensity. Highly sensitive and long-term surveillance will be necessary to verify elimination.
The onchocerciasis transmission models EPIONCHO and ONCHOSIM have been independently developed and used to explore the feasibility of eliminating onchocerciasis from Africa with mass (annual or biannual) distribution of ivermectin within the timeframes proposed by the World Health Organization (WHO) and endorsed by the 2012 London Declaration on Neglected Tropical Diseases (i.e. by 2020/2025). Based on the findings of our previous model comparison, we implemented technical refinements and tested the projections of EPIONCHO and ONCHOSIM against long-term epidemiological data from two West African transmission foci in Mali and Senegal where the observed prevalence of infection was brought to zero circa 2007–2009 after 15–17 years of mass ivermectin treatment. We simulated these interventions using programmatic information on the frequency and coverage of mass treatments and trained the model projections using longitudinal parasitological data from 27 communities, evaluating the projected outcome of elimination (local parasite extinction) or resurgence. We found that EPIONCHO and ONCHOSIM captured adequately the epidemiological trends during mass treatment but that resurgence, while never predicted by ONCHOSIM, was predicted by EPIONCHO in some communities with the highest (inferred) vector biting rates and associated pre-intervention endemicities. Resurgence can be extremely protracted such that low (microfilarial) prevalence between 1% and 5% can be maintained for 3–5 years before manifesting more prominently. We highlight that post-treatment and post-elimination surveillance protocols must be implemented for long enough and with high enough sensitivity to detect possible residual latent infections potentially indicative of resurgence. We also discuss uncertainty and differences between EPIONCHO and ONCHOSIM projections, the potential importance of vector control in high-transmission settings as a complementary intervention strategy, and the short remaining timeline for African countries to be ready to stop treatment safely and begin surveillance in order to meet the impending 2020/2025 elimination targets.
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Affiliation(s)
- Martin Walker
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK; Department of Pathobiology and Population Sciences and London Centre for Neglected Tropical Disease Research, Royal Veterinary College, Hawkshead Lane, Hatfield, AL9 7TA, UK.
| | - Wilma A Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Matthew A Dixon
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK; Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK
| | - Christian Bottomley
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK
| | - Lamine Diawara
- Inter-Country Support Team for West Africa, World Health Organization 158, Place de l'Indépendance 03 BP 7019, Ouagadougou 03, Burkina Faso
| | - Mamadou O Traoré
- Programme National de Lutte contre l'Onchocercose (PNLO), Direction Nationale de la Santé (DNS), B.P. 233, Bamako, Mali
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - María-Gloria Basáñez
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK; Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK
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Lessons Learned From Developing an Eradication Investment Case for Lymphatic Filariasis. ADVANCES IN PARASITOLOGY 2016; 94:393-417. [PMID: 27756458 DOI: 10.1016/bs.apar.2016.08.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In the last few years, the concepts of disease elimination and eradication have again gained consideration from the global health community, with Guinea worm disease (dracunculiasis) on track to become the first parasitic disease to be eradicated. Given the many complex and interlinking issues involved in committing to a disease eradication initiative, such commitments must be based on a solid assessment of a broad range of factors. In this chapter, we discuss the value and implications of undertaking a systematic and fact-based analysis of the overall situation prior to embarking on an elimination or eradication programme. As an example, we draw upon insights gained from a series of lymphatic filariasis (LF) studies from our research group that adopted an eradication investment case (EIC) framework. The justification for EICs, and related epidemiological, geospatial and other mathematical/operational research modelling, stems from the necessity for proper planning prior to committing to disease eradication. Across all considerations for LF eradication, including: time, treatments, level of investments necessary, health impact, cost-effectiveness, and broader economic benefits, scaling-up mass drug administration coverage to all endemic communities immediately provided the most favourable results. The coherent and consistent pursuit of eradication goals, operationally tailored to a given socioecological system and based on integrated measures of available tools will lead relatively rapidly to elimination in many parts of endemic areas and provide the cornerstone towards eradication.
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Michael E, Singh BK. Heterogeneous dynamics, robustness/fragility trade-offs, and the eradication of the macroparasitic disease, lymphatic filariasis. BMC Med 2016; 14:14. [PMID: 26822124 PMCID: PMC4731922 DOI: 10.1186/s12916-016-0557-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2015] [Accepted: 01/13/2016] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND The current WHO-led initiative to eradicate the macroparasitic disease, lymphatic filariasis (LF), based on single-dose annual mass drug administration (MDA) represents one of the largest health programs devised to reduce the burden of tropical diseases. However, despite the advances made in instituting large-scale MDA programs in affected countries, a challenge to meeting the goal of global eradication is the heterogeneous transmission of LF across endemic regions, and the impact that such complexity may have on the effort required to interrupt transmission in all socioecological settings. METHODS Here, we apply a Bayesian computer simulation procedure to fit transmission models of LF to field data assembled from 18 sites across the major LF endemic regions of Africa, Asia and Papua New Guinea, reflecting different ecological and vector characteristics, to investigate the impacts and implications of transmission heterogeneity and complexity on filarial infection dynamics, system robustness and control. RESULTS We find firstly that LF elimination thresholds varied significantly between the 18 study communities owing to site variations in transmission and initial ecological parameters. We highlight how this variation in thresholds lead to the need for applying variable durations of interventions across endemic communities for achieving LF elimination; however, a major new result is the finding that filarial population responses to interventions ultimately reflect outcomes of interplays between dynamics and the biological architectures and processes that generate robustness/fragility trade-offs in parasite transmission. Intervention simulations carried out in this study further show how understanding these factors is also key to the design of options that would effectively eliminate LF from all settings. In this regard, we find how including vector control into MDA programs may not only offer a countermeasure that will reliably increase system fragility globally across all settings and hence provide a control option robust to differential locality-specific transmission dynamics, but by simultaneously reducing transmission regime variability also permit more reliable macroscopic predictions of intervention effects. CONCLUSIONS Our results imply that a new approach, combining adaptive modelling of parasite transmission with the use of biological robustness as a design principle, is required if we are to both enhance understanding of complex parasitic infections and delineate options to facilitate their elimination effectively.
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Affiliation(s)
- Edwin Michael
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA.
| | - Brajendra K Singh
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA.
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Basáñez M, Walker M, Turner H, Coffeng L, de Vlas S, Stolk W. River Blindness: Mathematical Models for Control and Elimination. ADVANCES IN PARASITOLOGY 2016; 94:247-341. [PMID: 27756456 DOI: 10.1016/bs.apar.2016.08.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Human onchocerciasis (river blindness) is one of the few neglected tropical diseases (NTDs) whose control strategies have been informed by mathematical modelling. With the change in focus from elimination of the disease burden to elimination of Onchocerca volvulus, much remains to be done to refine, calibrate and validate existing models. Under the impetus of the NTD Modelling Consortium, the teams that developed EPIONCHO and ONCHOSIM have joined forces to compare and improve these frameworks to better assist ongoing elimination efforts. We review their current versions and describe how they are being used to address two key questions: (1) where can onchocerciasis be eliminated with current intervention strategies by 2020/2025? and (2) what alternative/complementary strategies could help to accelerate elimination where (1) cannot be achieved? The control and elimination of onchocerciasis from the African continent is at a crucial crossroad. The African Programme for Onchocerciasis Control closed at the end of 2015, and although a new platform for support and integration of NTD control has been launched, the disease will have to compete with a myriad of other national health priorities at a pivotal time in the road to elimination. However, never before had onchocerciasis control a better arsenal of intervention strategies as well as diagnostics. It is, therefore, timely to present two models of different geneses and modelling traditions as they come together to produce robust decision-support tools. We start by describing the structural and parametric assumptions of EPIONCHO and ONCHOSIM; we continue by summarizing the modelling of current treatment strategies with annual (or biannual) mass ivermectin distribution and introduce a number of alternative strategies, including other microfilaricidal therapies (such as moxidectin), macrofilaricidal (anti-wolbachial) treatments, focal vector control and the possibility of an onchocerciasis vaccine. We conclude by discussing challenges, opportunities and future directions.
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Moraga P, Cano J, Baggaley RF, Gyapong JO, Njenga SM, Nikolay B, Davies E, Rebollo MP, Pullan RL, Bockarie MJ, Hollingsworth TD, Gambhir M, Brooker SJ. Modelling the distribution and transmission intensity of lymphatic filariasis in sub-Saharan Africa prior to scaling up interventions: integrated use of geostatistical and mathematical modelling. Parasit Vectors 2015; 8:560. [PMID: 26496983 PMCID: PMC4620019 DOI: 10.1186/s13071-015-1166-x] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 10/14/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Lymphatic filariasis (LF) is one of the neglected tropical diseases targeted for global elimination. The ability to interrupt transmission is, partly, influenced by the underlying intensity of transmission and its geographical variation. This information can also help guide the design of targeted surveillance activities. The present study uses a combination of geostatistical and mathematical modelling to predict the prevalence and transmission intensity of LF prior to the implementation of large-scale control in sub-Saharan Africa. METHODS A systematic search of the literature was undertaken to identify surveys on the prevalence of Wuchereria bancrofti microfilaraemia (mf), based on blood smears, and on the prevalence of antigenaemia, based on the use of an immuno-chromatographic card test (ICT). Using a suite of environmental and demographic data, spatiotemporal multivariate models were fitted separately for mf prevalence and ICT-based prevalence within a Bayesian framework and used to make predictions for non-sampled areas. Maps of the dominant vector species of LF were also developed. The maps of predicted prevalence and vector distribution were linked to mathematical models of the transmission dynamics of LF to infer the intensity of transmission, quantified by the basic reproductive number (R0). RESULTS The literature search identified 1267 surveys that provide suitable data on the prevalence of mf and 2817 surveys that report the prevalence of antigenaemia. Distinct spatial predictions arose from the models for mf prevalence and ICT-based prevalence, with a wider geographical distribution when using ICT-based data. The vector distribution maps demonstrated the spatial variation of LF vector species. Mathematical modelling showed that the reproduction number (R0) estimates vary from 2.7 to 30, with large variations between and within regions. CONCLUSIONS LF transmission is highly heterogeneous, and the developed maps can help guide intervention, monitoring and surveillance strategies as countries progress towards LF elimination.
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Affiliation(s)
- Paula Moraga
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
| | - Jorge Cano
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
| | - Rebecca F Baggaley
- Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, UK.
| | - John O Gyapong
- School of Public Health, College of Health Sciences, University of Ghana, Legon, Accra, Ghana.
| | - Sammy M Njenga
- Eastern and Southern Africa Centre of International Parasite Control, Kenya Medical Research Institute, Nairobi, Kenya.
| | - Birgit Nikolay
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
| | | | - Maria P Rebollo
- NTD Support Center, Task Force for Global Health, Emory University, Atlanta, USA.
| | - Rachel L Pullan
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
| | - Moses J Bockarie
- Department of Vector Biology, Liverpool School for Tropical Medicine, Liverpool, UK.
| | - T Déirdre Hollingsworth
- Warwick Infectious Disease Epidemiology Research, Warwick Mathematics Institute, University of Warwick, Coventry, UK. .,School of Life Sciences, University of Warwick, Coventry, UK.
| | - Manoj Gambhir
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
| | - Simon J Brooker
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
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11
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Liu F, Porco TC, Amza A, Kadri B, Nassirou B, West SK, Bailey RL, Keenan JD, Lietman TM. Short-term forecasting of the prevalence of clinical trachoma: utility of including delayed recovery and tests for infection. Parasit Vectors 2015; 8:535. [PMID: 26489933 PMCID: PMC4618840 DOI: 10.1186/s13071-015-1115-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Accepted: 09/28/2015] [Indexed: 12/03/2022] Open
Abstract
Background The World Health Organization aims to control blinding trachoma by 2020. Decisions on whether to start and stop mass treatments and when to declare that control has been achieved are currently based on clinical examination data generated in population-based surveys. Thresholds are based on the district-level prevalence of trachomatous inflammation–follicular (TF) in children aged 1–9 years. Forecasts of which districts may and may not meet TF control goals by the 2020 target date could affect resource allocation in the next few years. Methods We constructed a hidden Markov model fit to the prevalence of two clinical signs of trachoma and PCR data in 24 communities from the recent PRET-Niger trial. The prevalence of TF in children in each community at 36 months was forecast given data from earlier time points. Forecasts were scored by the likelihood of the observed results. We assessed whether use of TF with additional TI and PCR data rather than just the use of TF alone improves forecasts, and separately whether incorporating a delay in TF recovery is beneficial. Results Including TI and PCR data did not significantly improve forecasts of TF. Forecasts of TF prevalence at 36 months by the model with the delay in TF recovery were significantly better than forecasts by the model without the delay in TF recovery (p = 0.003). A zero-inflated truncated normal observation model was better than a truncated normal observation model, and better than a sensitivity-specificity observation model. Conclusion The results in this study suggest that future studies could consider using just TF data for forecasting, and should include a delay in TF recovery. Trial registration Clinicaltrials.gov NCT00792922 Electronic supplementary material The online version of this article (doi:10.1186/s13071-015-1115-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Fengchen Liu
- F.I. Proctor Foundation, University of California San Francisco, 513 Parnassus, Medical Sciences 309A, San Francisco, CA, 94143-0944, USA.
| | - Travis C Porco
- F.I. Proctor Foundation, University of California San Francisco, 513 Parnassus, Medical Sciences 309A, San Francisco, CA, 94143-0944, USA. .,Department of Ophthalmology, University of California San Francisco, San Francisco, CA, USA. .,Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, CA, USA.
| | - Abdou Amza
- Programme FSS/Université Abdou Moumouni de Niamey, Programme National de Santé Oculaire, Niamey, Niger.
| | - Boubacar Kadri
- Programme FSS/Université Abdou Moumouni de Niamey, Programme National de Santé Oculaire, Niamey, Niger.
| | - Baido Nassirou
- Programme FSS/Université Abdou Moumouni de Niamey, Programme National de Santé Oculaire, Niamey, Niger.
| | - Sheila K West
- Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD, USA.
| | - Robin L Bailey
- Clinical Research Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.
| | - Jeremy D Keenan
- F.I. Proctor Foundation, University of California San Francisco, 513 Parnassus, Medical Sciences 309A, San Francisco, CA, 94143-0944, USA. .,Department of Ophthalmology, University of California San Francisco, San Francisco, CA, USA.
| | - Thomas M Lietman
- F.I. Proctor Foundation, University of California San Francisco, 513 Parnassus, Medical Sciences 309A, San Francisco, CA, 94143-0944, USA. .,Department of Ophthalmology, University of California San Francisco, San Francisco, CA, USA. .,Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, CA, USA.
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Gambhir M, Pinsent A. Possible changes in the transmissibility of trachoma following MDA and transmission reduction: implications for the GET2020 goals. Parasit Vectors 2015; 8:530. [PMID: 26490436 PMCID: PMC4618927 DOI: 10.1186/s13071-015-1133-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2015] [Accepted: 10/02/2015] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND The role of mass drug administration (MDA) and the implementation of transmission reduction measures are essential to successfully control and eliminate a wide range of NTDs, including the ocular disease trachoma. Immunity to trachoma infection acts by reducing the duration of an individual's infectious period and by reducing their infectivity with each successive infection. METHODS In this study, we use a model of trachoma infection, which includes population immunity, to explore the impact of treatment and transmission reduction measures on trachoma prevalence. Specifically, we investigate the possibility of increasing transmissibility of trachoma arising as MDA and transmission reduction measures are scaled up in endemic settings. RESULTS We demonstrate this increase in transmissibility by calculating the effective reproduction number during several simulated control programmes and show that it is related to a decrease in the level of immunity in the population. CONCLUSIONS This effect should be studied in the field by measuring the rate of return of infection and disease in at least two separate age groups. If the decline of population immunity is operating, it should be accounted for when planning for the GET2020 goal of eliminating blinding trachoma by 2020.
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Affiliation(s)
- Manoj Gambhir
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
| | - Amy Pinsent
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia
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Stolk WA, Stone C, de Vlas SJ. Modelling lymphatic filariasis transmission and control: modelling frameworks, lessons learned and future directions. ADVANCES IN PARASITOLOGY 2015; 87:249-91. [PMID: 25765197 DOI: 10.1016/bs.apar.2014.12.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Mathematical modelling provides a useful tool for policy making and planning in lymphatic filariasis control programmes, by providing trend forecasts based on sound scientific knowledge and principles. This is now especially true, in view of the ambitious target to eliminate lymphatic filariasis as a public health problem globally by the year 2020 and the short remaining timeline to achieve this. To meet this target, elimination programmes need to be accelerated, requiring further optimization of strategies and tailoring to local circumstances. Insights from epidemiological transmission models provide a useful basis. Two general models of lymphatic filariasis transmission and control are nowadays in use to support decision-making, namely a population-based deterministic model (EPIFIL) and an individual-based stochastic model (LYMFASIM). Model predictions confirm that lymphatic filariasis transmission can be interrupted by annual mass drug administration (MDA), but this may need to be continued much longer than the initially suggested 4-6 years in areas with high transmission intensity or poor treatment coverage. However, the models have not been validated against longitudinal data describing the impact of MDA programmes. Some critical issues remain to be incorporated in one or both of the models to make predictions on elimination more realistic, including the possible occurrence of systematic noncompliance, the risk of emerging parasite resistance to anthelmintic drugs, and spatial heterogeneities. Rapid advances are needed to maximize the utility of models in decision-making for the ongoing ambitious lymphatic filariasis elimination programmes.
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Affiliation(s)
- Wilma A Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, The Netherlands
| | - Chris Stone
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, The Netherlands
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