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Kaye PM, Matlashewski G, Mohan S, Le Rutte E, Mondal D, Khamesipour A, Malvolti S. Vaccine value profile for leishmaniasis. Vaccine 2023; 41 Suppl 2:S153-S175. [PMID: 37951693 DOI: 10.1016/j.vaccine.2023.01.057] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 12/22/2022] [Accepted: 01/24/2023] [Indexed: 11/14/2023]
Abstract
Leishmania infections are global, occurring in 98 countries and all World Health Organization (WHO) regions with 600 million to 1 billion people at risk of infection. Visceral leishmaniasis is associated with almost 20,000 reported deaths annually, with children under 5 years of age being at the greatest risk of mortality. Amongst WHO-recognised Neglected Tropical Diseases (NTDs), leishmaniasis is one of the most important in terms of mortality and morbidity. With an increasing global burden of disease and a growing threat from climate change, urbanisation and drug resistance, there remains an imperative to develop leishmaniasis vaccines. New tools to understand correlates of protection and to assess vaccine efficacy are being developed to ease the transition into larger scale efficacy trials or provide alternate routes to licensure. Early indications suggest a diverse portfolio of manufacturers exists in endemic countries with an appetite to develop leishmaniasis vaccines. This Vaccine Value Profile (VVP) provides a high-level, comprehensive assessment of the currently available data to inform the potential public health, economic, and societal value of leishmaniasis vaccines. The leishmaniasis VVP was developed by a working group of subject matter experts from academia, public health groups, policy organizations, and non-profit organizations. All contributors have extensive expertise on various elements of the leishmaniasis VVP and have collectively described the state of knowledge and identified the current gaps. The VVP was developed using only existing and publicly available information.
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Affiliation(s)
- Paul M Kaye
- York Biomedical Research Institute, Hull York Medical School, University of York, York, UK.
| | - Greg Matlashewski
- Department of Microbiology and Immunology, McGill University, Montreal, Quebec, Canada.
| | - Sakshi Mohan
- Center for Health Economics (CHE), University of York, York, UK.
| | - Epke Le Rutte
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
| | - Dinesh Mondal
- Laboratory Sciences and Services Division, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh.
| | - Ali Khamesipour
- Center for Research and Training in Skin Diseases and Leprosy, Tehran University of Medical Sciences, Tehran, Iran.
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Kaye PM, Mohan S, Mantel C, Malhame M, Revill P, Le Rutte E, Parkash V, Layton AM, Lacey CJ, Malvolti S. Overcoming roadblocks in the development of vaccines for leishmaniasis. Expert Rev Vaccines 2021; 20:1419-1430. [PMID: 34727814 PMCID: PMC9844205 DOI: 10.1080/14760584.2021.1990043] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 10/04/2021] [Indexed: 01/21/2023]
Abstract
INTRODUCTION The leishmaniases represent a group of parasitic diseases caused by infection with one of several species of Leishmania parasites. Disease presentation varies because of differences in parasite and host genetics and may be influenced by additional factors such as host nutritional status or co-infection. Studies in experimental models of Leishmania infection, vaccination of companion animals and human epidemiological data suggest that many forms of leishmaniasis could be prevented by vaccination, but no vaccines are currently available for human use. AREAS COVERED We describe some of the existing roadblocks to the development and implementation of an effective leishmaniasis vaccine, based on a review of recent literature found on PubMed, BioRxiv and MedRxiv. In addition to discussing scientific unknowns that hinder vaccine candidate identification and selection, we explore gaps in knowledge regarding the commercial and public health value propositions underpinning vaccine development and provide a route map for future research and advocacy. EXPERT OPINION Despite significant progress, leishmaniasis vaccine development remains hindered by significant gaps in understanding that span the vaccine development pipeline. Increased coordination and adoption of a more holistic view to vaccine development will be required to ensure more rapid progress in the years ahead.
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Affiliation(s)
- Paul M. Kaye
- York Biomedical Research Institute, Hull York Medical School, University of York, Heslington, York, UK
| | - Sakshi Mohan
- Centre for Health Economics, University of York, Heslington, York, UK
| | | | | | - Paul Revill
- Centre for Health Economics, University of York, Heslington, York, UK
| | - Epke Le Rutte
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Vivak Parkash
- York Biomedical Research Institute, Hull York Medical School, University of York, Heslington, York, UK
| | - Alison M. Layton
- York Biomedical Research Institute, Hull York Medical School, University of York, Heslington, York, UK
| | - Charles J.N. Lacey
- York Biomedical Research Institute, Hull York Medical School, University of York, Heslington, York, UK
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Fortunato AK, Glasser CP, Watson JA, Lu Y, Rychtář J, Taylor D. Mathematical modelling of the use of insecticide-treated nets for elimination of visceral leishmaniasis in Bihar, India. ROYAL SOCIETY OPEN SCIENCE 2021; 8:201960. [PMID: 34234949 PMCID: PMC8242840 DOI: 10.1098/rsos.201960] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 05/24/2021] [Indexed: 05/27/2023]
Abstract
Visceral leishmaniasis (VL) is a deadly neglected tropical disease caused by a parasite Leishmania donovani and spread by female sand flies Phlebotomus argentipes. There is conflicting evidence regarding the role of insecticide-treated nets (ITNs) on the prevention of VL. Numerous studies demonstrated the effectiveness of ITNs. However, KalaNet, a large trial in Nepal and India did not support those findings. The purpose of this paper is to gain insight into the situation by mathematical modelling. We expand a mathematical model of VL transmission based on the KalaNet trial and incorporate the use of ITNs explicitly into the model. One of the major contributions of this work is that we calibrate the model based on the available epidemiological data, generally independent of the KalaNet trial. We validate the model on data collected during the KalaNet trial. We conclude that in order to eliminate VL, the ITN usage would have to stay above 96%. This is higher than the 91% ITNs use at the end of the trial which may explain why the trial did not show a positive effect from ITNs. At the same time, our model indicates that asymptomatic individuals play a crucial role in VL transmission.
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Affiliation(s)
- Anna K. Fortunato
- Department of Mathematics, University of Richmond, Richmond, VA 23173, USA
| | - Casey P. Glasser
- Department of Mathematics, Virginia Tech, Blacksburg, VA 24061-1026, USA
| | - Joy A. Watson
- Department of Mathematics and Economics, Virginia State University, Petersburg, VA 23806, USA
| | - Yongjin Lu
- Department of Mathematics and Economics, Virginia State University, Petersburg, VA 23806, USA
| | - Jan Rychtář
- Department of Mathematics and Applied Mathematics, Virginia Commonwealth University, Richmond, VA 23284-2014, USA
| | - Dewey Taylor
- Department of Mathematics and Applied Mathematics, Virginia Commonwealth University, Richmond, VA 23284-2014, USA
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Le Rutte EA, Chapman LAC, Coffeng LE, Ruiz-Postigo JA, Olliaro PL, Adams ER, Hasker EC, Boelaert MC, Hollingsworth TD, Medley GF, de Vlas SJ. Policy Recommendations From Transmission Modeling for the Elimination of Visceral Leishmaniasis in the Indian Subcontinent. Clin Infect Dis 2019; 66:S301-S308. [PMID: 29860292 PMCID: PMC5982727 DOI: 10.1093/cid/ciy007] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Background Visceral leishmaniasis (VL) has been targeted by the World Health Organization (WHO) and 5 countries in the Indian subcontinent for elimination as a public health problem. To achieve this target, the WHO has developed guidelines consisting of 4 phases of different levels of interventions, based on vector control through indoor residual spraying of insecticide (IRS) and active case detection (ACD). Mathematical transmission models of VL are increasingly used for planning and assessing the efficacy of interventions and evaluating the intensity and timescale required to achieve the elimination target. Methods This paper draws together the key policy-relevant conclusions from recent transmission modeling of VL, and presents new predictions for VL incidence under the interventions recommended by the WHO using the latest transmission models. Results The model predictions suggest that the current WHO guidelines should be sufficient to reach the elimination target in areas that had medium VL endemicities (up to 5 VL cases per 10000 population per year) prior to the start of interventions. However, additional interventions, such as extending the WHO attack phase (intensive IRS and ACD), may be required to bring forward elimination in regions with high precontrol endemicities, depending on the relative infectiousness of different disease stages. Conclusions The potential hurdle that asymptomatic and, in particular, post-kala-azar dermal leishmaniasis cases may pose to reaching and sustaining the target needs to be addressed. As VL incidence decreases, the pool of immunologically naive individuals will grow, creating the potential for new outbreaks.
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Affiliation(s)
- Epke A Le Rutte
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, The Netherlands
| | - Lloyd A C Chapman
- Zeeman Institute, University of Warwick, Coventry, United Kingdom.,London School of Hygiene and Tropical Medicine, United Kingdom
| | - Luc E Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, The Netherlands
| | | | - Piero L Olliaro
- Special Programme for Research and Training in Tropical Diseases, World Health Organization, Geneva, Switzerland
| | - Emily R Adams
- Liverpool School of Tropical Medicine, United Kingdom
| | | | | | - T Deirdre Hollingsworth
- Zeeman Institute, University of Warwick, Coventry, United Kingdom.,Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford
| | - Graham F Medley
- London School of Hygiene and Tropical Medicine, United Kingdom
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, The Netherlands
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Buckingham-Jeffery E, Hill EM, Datta S, Dilger E, Courtenay O. Spatio-temporal modelling of Leishmania infantum infection among domestic dogs: a simulation study and sensitivity analysis applied to rural Brazil. Parasit Vectors 2019; 12:215. [PMID: 31064395 PMCID: PMC6505121 DOI: 10.1186/s13071-019-3430-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 04/04/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The parasite Leishmania infantum causes zoonotic visceral leishmaniasis (VL), a potentially fatal vector-borne disease of canids and humans. Zoonotic VL poses a significant risk to public health, with regions of Latin America being particularly afflicted by the disease. Leishmania infantum parasites are transmitted between hosts during blood-feeding by infected female phlebotomine sand flies. With a principal reservoir host of L. infantum being domestic dogs, limiting prevalence in this reservoir may result in a reduced risk of infection for the human population. To this end, a primary focus of research efforts has been to understand disease transmission dynamics among dogs. One way this can be achieved is through the use of mathematical models. METHODS We have developed a stochastic, spatial, individual-based mechanistic model of L. infantum transmission in domestic dogs. The model framework was applied to a rural Brazilian village setting with parameter values informed by fieldwork and laboratory data. To ensure household and sand fly populations were realistic, we statistically fitted distributions for these entities to existing survey data. To identify the model parameters of highest importance, we performed a stochastic parameter sensitivity analysis of the prevalence of infection among dogs to the model parameters. RESULTS We computed parametric distributions for the number of humans and animals per household and a non-parametric temporal profile for sand fly abundance. The stochastic parameter sensitivity analysis determined prevalence of L. infantum infection in dogs to be most strongly affected by the sand fly associated parameters and the proportion of immigrant dogs already infected with L. infantum parasites. CONCLUSIONS Establishing the model parameters with the highest sensitivity of average L. infantum infection prevalence in dogs to their variation helps motivate future data collection efforts focusing on these elements. Moreover, the proposed mechanistic modelling framework provides a foundation that can be expanded to explore spatial patterns of zoonotic VL in humans and to assess spatially targeted interventions.
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Affiliation(s)
- Elizabeth Buckingham-Jeffery
- School of Mathematics, University of Manchester, Manchester, UK.
- Zeeman Institute: SBIDER (Systems Biology & Infectious Disease Epidemiology Research), University of Warwick, Coventry, UK.
| | - Edward M Hill
- Zeeman Institute: SBIDER (Systems Biology & Infectious Disease Epidemiology Research), University of Warwick, Coventry, UK
- Warwick Mathematics Institute, University of Warwick, Coventry, UK
| | - Samik Datta
- Population Modelling Group, National Institute of Water and Atmospheric Research, Wellington, New Zealand
- Zeeman Institute: SBIDER (Systems Biology & Infectious Disease Epidemiology Research), University of Warwick, Coventry, UK
| | - Erin Dilger
- Zeeman Institute: SBIDER (Systems Biology & Infectious Disease Epidemiology Research), University of Warwick, Coventry, UK
- School of Life Sciences, University of Warwick, Coventry, UK
| | - Orin Courtenay
- Zeeman Institute: SBIDER (Systems Biology & Infectious Disease Epidemiology Research), University of Warwick, Coventry, UK
- School of Life Sciences, University of Warwick, Coventry, UK
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Chapman LAC, Morgan ALK, Adams ER, Bern C, Medley GF, Hollingsworth TD. Age trends in asymptomatic and symptomatic Leishmania donovani infection in the Indian subcontinent: A review and analysis of data from diagnostic and epidemiological studies. PLoS Negl Trop Dis 2018; 12:e0006803. [PMID: 30521526 PMCID: PMC6283524 DOI: 10.1371/journal.pntd.0006803] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 08/30/2018] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND Age patterns in asymptomatic and symptomatic infection with Leishmania donovani, the causative agent of visceral leishmaniasis (VL) in the Indian subcontinent (ISC), are currently poorly understood. Age-stratified serology and infection incidence have been used to assess transmission levels of other diseases, which suggests that they may also be of use for monitoring and targeting control programmes to achieve elimination of VL and should be included in VL transmission dynamic models. We therefore analysed available age-stratified data on both disease incidence and prevalence of immune markers with the aim of collating the currently available data, estimating rates of infection, and informing modelling and future data collection. METHODOLOGY/PRINCIPAL FINDINGS A systematic literature search yielded 13 infection prevalence and 7 VL incidence studies meeting the inclusion criteria. Statistical tests were performed to identify trends by age, and according to diagnostic cut-off. Simple reversible catalytic models with age-independent and age-dependent infection rates were fitted to the prevalence data to estimate infection and reversion rates, and to test different hypotheses about the origin of variation in these rates. Most of the studies showed an increase in infection prevalence with age: from ≲10% seroprevalence (<20% Leishmanin skin test (LST) positivity) for 0-10-year-olds to >10% seroprevalence (>20% LST-positivity) for 30-40-year-olds, but overall prevalence varied considerably between studies. VL incidence was lower amongst 0-5-year-olds than older age groups in most studies; most showing a peak in incidence between ages 5 and 20. The age-independent catalytic model provided the best overall fit to the infection prevalence data, but the estimated rates for the less parsimonious age-dependent model were much closer to estimates from longitudinal studies, suggesting that infection rates may increase with age. CONCLUSIONS/SIGNIFICANCE Age patterns in asymptomatic infection prevalence and VL incidence in the ISC vary considerably with geographical location and time period. The increase in infection prevalence with age and peaked age-VL-incidence distribution may be due to lower exposure to infectious sandfly bites in young children, but also suggest that acquired immunity to the parasite increases with age. However, poor standardisation of serological tests makes it difficult to compare data from different studies and draw firm conclusions about drivers of variation in observed age patterns.
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Affiliation(s)
- Lloyd A. C. Chapman
- Zeeman Institute, University of Warwick, Coventry, United Kingdom
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
- Centre for Mathematical Modelling of Infectious Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Alex L. K. Morgan
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
- School of Biological Sciences, University of Edinburgh, Edinbugh, United Kingdom
| | - Emily R. Adams
- Liverpool School of Tropical Medicine, Liverpool, United Kingdom
| | - Caryn Bern
- Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, United States of America
| | - Graham F. Medley
- Centre for Mathematical Modelling of Infectious Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - T. Déirdre Hollingsworth
- Zeeman Institute, University of Warwick, Coventry, United Kingdom
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, United Kingdom
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Bulstra CA, Le Rutte EA, Malaviya P, Hasker EC, Coffeng LE, Picado A, Singh OP, Boelaert MC, de Vlas SJ, Sundar S. Visceral leishmaniasis: Spatiotemporal heterogeneity and drivers underlying the hotspots in Muzaffarpur, Bihar, India. PLoS Negl Trop Dis 2018; 12:e0006888. [PMID: 30521529 PMCID: PMC6283467 DOI: 10.1371/journal.pntd.0006888] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 10/01/2018] [Indexed: 01/03/2023] Open
Abstract
BACKGROUND Despite the overall decrease in visceral leishmaniasis (VL) incidence on the Indian subcontinent, there remain spatiotemporal clusters or 'hotspots' of new cases. The characteristics of these hotspots, underlying transmission dynamics, and their importance for shaping control strategies are not yet fully understood and are investigated in this study for a VL endemic area of ~100,000 inhabitants in Bihar, India between 2007-2015. METHODOLOGY/PRINCIPAL FINDINGS VL incidence (cases/10,000/year) dropped from 12.3 in 2007 to 0.9 in 2015, which is just below the World Health Organizations' threshold for elimination as a public health problem. Clustering of VL was assessed between subvillages (hamlets), using multiple geospatial and (spatio)temporal autocorrelation and hotspot analyses. One to three hotspots were identified each year, often persisting for 1-5 successive years with a modal radius of ~500m. The relative risk of having VL was 5-86 times higher for inhabitants of hotspots, compared to those living outside hotspots. Hotspots harbour significantly more households from the two lowest asset quintiles (as proxy for socio-economic status). Overall, children and young adelescents (5-14 years) have the highest risk for VL, but within hotspots and at the start of outbreaks, older age groups (35+ years) show a comparable high risk. CONCLUSIONS/SIGNIFICANCE This study demonstrates significant spatiotemporal heterogeneity in VL incidence at subdistrict level. The association between poverty and hotspots confirms that VL is a disease of 'the poorest of the poor' and age patterns suggest a potential role of waning immunity as underlying driver of hotspots. The recommended insecticide spraying radius of 500m around detected VL cases corresponds to the modal hotspot radius found in this study. Additional data on immunity and asymptomatic infection, and the development of spatiotemporally explicit transmission models that simulate hotspot dynamics and predict the impact of interventions at the smaller geographical scale will be crucial tools in sustaining elimination.
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Affiliation(s)
- Caroline A. Bulstra
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Epke A. Le Rutte
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
- Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium
| | - Paritosh Malaviya
- Department of Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
| | - Epco C. Hasker
- Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium
| | - Luc E. Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Albert Picado
- ISGlobal, Barcelona Institute for Global Health, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain
- Foundation for Innovative New Diagnostics (FIND), Geneva, Switzerland
| | - Om Prakash Singh
- Department of Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
| | - Marleen C. Boelaert
- Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium
| | - Sake J. de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Shyam Sundar
- Department of Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
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Hollingsworth TD. Counting Down the 2020 Goals for 9 Neglected Tropical Diseases: What Have We Learned From Quantitative Analysis and Transmission Modeling? Clin Infect Dis 2018; 66:S237-S244. [PMID: 29860293 PMCID: PMC5982793 DOI: 10.1093/cid/ciy284] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The control of neglected tropical diseases (NTDs) has received huge investment in recent years, leading to large reductions in morbidity. In 2012, the World Health Organization set ambitious targets for eliminating many of these diseases as a public health problem by 2020, an aspiration that was supported by donations of treatments, intervention materials, and funding committed by a broad partnership of stakeholders in the London Declaration on NTDs. Alongside these efforts, there has been an increasing role for quantitative analysis and modeling to support the achievement of these goals through evaluation of the likely impact of interventions, the factors that could undermine these achievements, and the role of new diagnostics and treatments in reducing transmission. In this special issue, we aim to summarize those insights in an accessible way. This article acts as an introduction to the special issue, outlining key concepts in NTDs and insights from modeling as we approach 2020.
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Affiliation(s)
- T Déirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, Nuffideld Department of Medicine, University of Oxford, United Kingdom
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Zijlstra EE, Alves F, Rijal S, Arana B, Alvar J. Post-kala-azar dermal leishmaniasis in the Indian subcontinent: A threat to the South-East Asia Region Kala-azar Elimination Programme. PLoS Negl Trop Dis 2017; 11:e0005877. [PMID: 29145397 PMCID: PMC5689828 DOI: 10.1371/journal.pntd.0005877] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Background The South-East Asia Region Kala-azar Elimination Programme (KAEP) is expected to enter the consolidation phase in 2017, which focuses on case detection, vector control, and identifying potential sources of infection. Post-kala-azar dermal leishmaniasis (PKDL) is thought to play a role in the recurrence of visceral leishmaniasis (VL)/kala-azar outbreaks, and control of PKDL is among the priorities of the KAEP. Methodology and principal finding We reviewed the literature with regard to PKDL in Asia and interpreted the findings in relation to current intervention methods in the KAEP in order to make recommendations. There is a considerable knowledge gap regarding the pathophysiology of VL and PKDL, especially the underlying immune responses. Risk factors (of which previous VL treatments may be most important) are poorly understood and need to be better defined. The role of PKDL patients in transmission is largely unknown, and there is insufficient information about the importance of duration, distribution and severity of the rash, time of onset, and self-healing. Current intervention methods focus on active case detection and treatment of all PKDL cases with miltefosine while there is increasing drug resistance. The prevention of PKDL by improved VL treatment currently receives insufficient attention. Conclusion and significance PKDL is a heterogeneous and dynamic condition, and patients differ with regard to time of onset after VL, chronicity, and distribution and appearance of the rash, as well as immune responses (including tendency to self-heal), all of which may vary over time. It is essential to fully describe the pathophysiology in order to make informed decisions on the most cost-effective approach. Emphasis should be on early detection of those who contribute to transmission and those who are in need of treatment, for whom short-course, effective, and safe drug regimens should be available. The prevention of PKDL should be emphasised by innovative and improved treatment for VL, which may include immunomodulation.
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Affiliation(s)
- Eduard E. Zijlstra
- Drugs for Neglected Diseases initiative, Geneva, Switzerland
- Rotterdam Centre for Tropical Medicine, Rotterdam, the Netherlands
- * E-mail:
| | - Fabiana Alves
- Drugs for Neglected Diseases initiative, Geneva, Switzerland
| | - Suman Rijal
- Drugs for Neglected Diseases initiative, India Office, New Delhi, India
| | - Byron Arana
- Drugs for Neglected Diseases initiative, Geneva, Switzerland
| | - Jorge Alvar
- Drugs for Neglected Diseases initiative, Geneva, Switzerland
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Kamiya T, Greischar MA, Mideo N. Epidemiological consequences of immune sensitisation by pre-exposure to vector saliva. PLoS Negl Trop Dis 2017; 11:e0005956. [PMID: 28991904 PMCID: PMC5648264 DOI: 10.1371/journal.pntd.0005956] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 10/19/2017] [Accepted: 09/12/2017] [Indexed: 11/25/2022] Open
Abstract
Blood-feeding arthropods—like mosquitoes, sand flies, and ticks—transmit many diseases that impose serious public health and economic burdens. When a blood-feeding arthropod bites a mammal, it injects saliva containing immunogenic compounds that facilitate feeding. Evidence from Leishmania, Plasmodium and arboviral infections suggests that the immune responses elicited by pre-exposure to arthropod saliva can alter disease progression if the host later becomes infected. Such pre-sensitisation of host immunity has been reported to both exacerbate and limit infection symptoms, depending on the system in question, with potential implications for recovery. To explore if and how immune pre-sensitisation alters the effects of vector control, we develop a general model of vector-borne disease. We show that the abundance of pre-sensitised infected hosts should increase when control efforts moderately increase vector mortality rates. If immune pre-sensitisation leads to more rapid clearance of infection, increasing vector mortality rates may achieve greater than expected disease control. However, when immune pre-sensitisation prolongs the duration of infection, e.g., through mildly symptomatic cases for which treatment is unlikely to be sought, vector control can actually increase the total number of infected hosts. The rising infections may go unnoticed unless active surveillance methods are used to detect such sub-clinical individuals, who could provide long-lasting reservoirs for transmission and suffer long-term health consequences of those sub-clinical infections. Sensitivity analysis suggests that these negative consequences could be mitigated through integrated vector management. While the effect of saliva pre-exposure on acute symptoms is well-studied for leishmaniasis, the immunological and clinical consequences are largely uncharted for other vector-parasite-host combinations. We find a large range of plausible epidemiological outcomes, positive and negative for public health, underscoring the need to quantify how immune pre-sensitisation modulates recovery and transmission rates in vector-borne diseases. Many diseases of health and economic importance are transmitted by arthropod vectors, like mosquitoes, sand flies, and ticks. When a blood-feeding arthropod bites a mammal, it injects saliva containing compounds that facilitate feeding. The immune responses elicited by previous exposure to vector saliva can alter disease severity if the host later becomes infected. Such pre-sensitisation of host immunity has been linked to either exacerbation or mitigation of symptoms in a number of disease systems. We develop a general model of vector-borne disease to examine how vector control efforts alter the frequency of immune pre-sensitisation and thus change the epidemiological impact of control. We show that the abundance of pre-sensitised infected hosts should increase when control efforts moderately increase vector mortality rates. When immune pre-sensitisation leads to longer infections—by generating sub-clinical cases for which treatment is not rapidly sought—killing vectors can lead to unexpected increases in the number of infected hosts. The rising case burden may go unnoticed unless sub-clinical individuals are tested for infection. Conversely, if immune pre-sensitisation leads to more rapid clearance of infection, increasing vector mortality rates may achieve greater than expected disease control. Our findings highlight the need to quantify how immune pre-sensitisation modulates clinical outcomes and parasite transmission in humans.
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Affiliation(s)
- Tsukushi Kamiya
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Megan A Greischar
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Nicole Mideo
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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DebRoy S, Prosper O, Mishoe A, Mubayi A. Challenges in modeling complexity of neglected tropical diseases: a review of dynamics of visceral leishmaniasis in resource limited settings. Emerg Themes Epidemiol 2017; 14:10. [PMID: 28936226 PMCID: PMC5604165 DOI: 10.1186/s12982-017-0065-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 08/30/2017] [Indexed: 11/10/2022] Open
Abstract
OBJECTIVES Neglected tropical diseases (NTD), account for a large proportion of the global disease burden, and their control faces several challenges including diminishing human and financial resources for those distressed from such diseases. Visceral leishmaniasis (VL), the second-largest parasitic killer (after malaria) and an NTD affects poor populations and causes considerable cost to the affected individuals. Mathematical models can serve as a critical and cost-effective tool for understanding VL dynamics, however, complex array of socio-economic factors affecting its dynamics need to be identified and appropriately incorporated within a dynamical modeling framework. This study reviews literature on vector-borne diseases and collects challenges and successes related to the modeling of transmission dynamics of VL. Possible ways of creating a comprehensive mathematical model is also discussed. METHODS Published literature in three categories are reviewed: (i) identifying non-traditional but critical mechanisms for VL transmission in resource limited regions, (ii) mathematical models used for dynamics of Leishmaniasis and other related vector borne infectious diseases and (iii) examples of modeling that have the potential to capture identified mechanisms of VL to study its dynamics. RESULTS This review suggests that VL elimination have not been achieved yet because existing transmission dynamics models for VL fails to capture relevant local socio-economic risk factors. This study identifies critical risk factors of VL and distribute them in six categories (atmosphere, access, availability, awareness, adherence, and accedence). The study also suggests novel quantitative models, parts of it are borrowed from other non-neglected diseases, for incorporating these factors and using them to understand VL dynamics and evaluating control programs for achieving VL elimination in a resource-limited environment. CONCLUSIONS Controlling VL is expensive for local communities in endemic countries where individuals remain in the vicious cycle of disease and poverty. Smarter public investment in control programs would not only decrease the VL disease burden but will also help to alleviate poverty. However, dynamical models are necessary to evaluate intervention strategies to formulate a cost-effective optimal policy for eradication of VL.
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Affiliation(s)
- Swati DebRoy
- Department of Mathematics and Computational Science, University of South Carolina, Beaufort, SC USA
| | - Olivia Prosper
- Department of Mathematics, University of Kentucky, Lexington, KY USA
| | - Austin Mishoe
- Department of Mathematics and Computational Science, University of South Carolina, Beaufort, SC USA
| | - Anuj Mubayi
- Simon A. Levin-Mathematical Computational and Modeling Science Center, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ USA
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12
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Gomez SA, Picado A. Systemic insecticides used in dogs: potential candidates for phlebotomine vector control? Trop Med Int Health 2017; 22:755-764. [PMID: 28326655 DOI: 10.1111/tmi.12870] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Zoonotic visceral leishmaniasis (ZVL) is a public health problem endemic in some countries. Current control measures, in particular culling infected dogs, have not reduced ZVL incidence in humans. We evaluated the use of five systemic insecticides (spinosad, fluralaner, afoxolaner, sarolaner and moxidectin) currently used in dogs for other purposes (e.g. tick, flea control) in controlling ZVL transmission. The anti-phlebotomine capacity of these compounds confirmed in experimental studies makes their use in ZVL control programmes very promising. Limitations and benefits of using this new control tool are compared to current practices.
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Affiliation(s)
| | - Albert Picado
- Barcelona Institute for Global Health, Barcelona, Spain
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13
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Ghosh I, Sardar T, Chattopadhyay J. A Mathematical Study to Control Visceral Leishmaniasis: An Application to South Sudan. Bull Math Biol 2017; 79:1100-1134. [PMID: 28357614 DOI: 10.1007/s11538-017-0274-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 03/22/2017] [Indexed: 01/27/2023]
Abstract
In this manuscript, we propose and analyze a compartmental model of visceral leishmaniasis (VL). We model the human population with six compartments including asymptomatic, symptomatic and PKDL-infected, animal population as second host and sandfly population as the vector. Furthermore, the non-adult stage of the sandfly population is introduced in the system, which was not considered before in the literature. We show that the increase in the number of host of sandfly population generates a backward bifurcation. Thus, multiple hosts will cause disease persistence even if the basic reproduction number ([Formula: see text]) is below unity. We perform a sensitivity analysis of important model parameters with respect to some epidemiologically significant responses. We validate our model by calibrating it to weekly VL incidence data from South Sudan for the year 2013. We perform cost-effectiveness analysis on different interventions: treatment, non-adult control, adult control and their different layered combinations based on their implementation cost (in USD) and case reduction. We also use a global sensitivity analysis technique to understand the effect of important parameters of our model on the implementation cost of different controls. This cost-effectiveness study and cost-sensitivity analysis are relatively new in existing literature of this disease.
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Affiliation(s)
- Indrajit Ghosh
- Agricultural and Ecological Research Unit, Indian Statistical Institute, 203, B. T. Road, Kolkata, West Bengal, 700108, India
| | - Tridip Sardar
- Department of Mathematics, Dinabandhu Andrews College, Baishnabghata, P.O. Garia, Dist. 24 Paraganas (S), Kolkata, West Bengal, 700084, India
| | - Joydev Chattopadhyay
- Agricultural and Ecological Research Unit, Indian Statistical Institute, 203, B. T. Road, Kolkata, West Bengal, 700108, India.
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14
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Le Rutte EA, Chapman LAC, Coffeng LE, Jervis S, Hasker EC, Dwivedi S, Karthick M, Das A, Mahapatra T, Chaudhuri I, Boelaert MC, Medley GF, Srikantiah S, Hollingsworth TD, de Vlas SJ. Elimination of visceral leishmaniasis in the Indian subcontinent: a comparison of predictions from three transmission models. Epidemics 2017; 18:67-80. [PMID: 28279458 PMCID: PMC5340844 DOI: 10.1016/j.epidem.2017.01.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 01/06/2017] [Accepted: 01/07/2017] [Indexed: 12/23/2022] Open
Abstract
We present three transmission models of visceral leishmaniasis (VL) in the Indian subcontinent (ISC) with structural differences regarding the disease stage that provides the main contribution to transmission, including models with a prominent role of asymptomatic infection, and fit them to recent case data from 8 endemic districts in Bihar, India. Following a geographical cross-validation of the models, we compare their predictions for achieving the WHO VL elimination targets with ongoing treatment and vector control strategies. All the transmission models suggest that the WHO elimination target (<1 new VL case per 10,000 capita per year at sub-district level) is likely to be met in Bihar, India, before or close to 2020 in sub-districts with a pre-control incidence of 10 VL cases per 10,000 people per year or less, when current intervention levels (60% coverage of indoor residual spraying (IRS) of insecticide and a delay of 40days from onset of symptoms to treatment (OT)) are maintained, given the accuracy and generalizability of the existing data regarding incidence and IRS coverage. In settings with a pre-control endemicity level of 5/10,000, increasing the effective IRS coverage from 60 to 80% is predicted to lead to elimination of VL 1-3 years earlier (depending on the particular model), and decreasing OT from 40 to 20days to bring elimination forward by approximately 1year. However, in all instances the models suggest that L. donovani transmission will continue after 2020 and thus that surveillance and control measures need to remain in place until the longer-term aim of breaking transmission is achieved.
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Affiliation(s)
- Epke A Le Rutte
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands.
| | - Lloyd A C Chapman
- School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry CV4 7AL, United Kingdom
| | - Luc E Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Sarah Jervis
- School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry CV4 7AL, United Kingdom
| | - Epco C Hasker
- Institute of Tropical Medicine, Nationalestraat 155, 2000 Antwerp, Belgium
| | - Shweta Dwivedi
- CARE India Solutions for Sustainable Development, Patna, Bihar, India
| | - Morchan Karthick
- CARE India Solutions for Sustainable Development, Patna, Bihar, India
| | - Aritra Das
- CARE India Solutions for Sustainable Development, Patna, Bihar, India
| | - Tanmay Mahapatra
- CARE India Solutions for Sustainable Development, Patna, Bihar, India
| | | | - Marleen C Boelaert
- Institute of Tropical Medicine, Nationalestraat 155, 2000 Antwerp, Belgium
| | - Graham F Medley
- London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom
| | | | - T Deirdre Hollingsworth
- School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry CV4 7AL, United Kingdom
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands
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15
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Biswas S, Subramanian A, ELMojtaba IM, Chattopadhyay J, Sarkar RR. Optimal combinations of control strategies and cost-effective analysis for visceral leishmaniasis disease transmission. PLoS One 2017; 12:e0172465. [PMID: 28222162 PMCID: PMC5319670 DOI: 10.1371/journal.pone.0172465] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 02/06/2017] [Indexed: 11/29/2022] Open
Abstract
Visceral leishmaniasis (VL) is a deadly neglected tropical disease that poses a serious problem in various countries all over the world. Implementation of various intervention strategies fail in controlling the spread of this disease due to issues of parasite drug resistance and resistance of sandfly vectors to insecticide sprays. Due to this, policy makers need to develop novel strategies or resort to a combination of multiple intervention strategies to control the spread of the disease. To address this issue, we propose an extensive SIR-type model for anthroponotic visceral leishmaniasis transmission with seasonal fluctuations modeled in the form of periodic sandfly biting rate. Fitting the model for real data reported in South Sudan, we estimate the model parameters and compare the model predictions with known VL cases. Using optimal control theory, we study the effects of popular control strategies namely, drug-based treatment of symptomatic and PKDL-infected individuals, insecticide treated bednets and spray of insecticides on the dynamics of infected human and vector populations. We propose that the strategies remain ineffective in curbing the disease individually, as opposed to the use of optimal combinations of the mentioned strategies. Testing the model for different optimal combinations while considering periodic seasonal fluctuations, we find that the optimal combination of treatment of individuals and insecticide sprays perform well in controlling the disease for the time period of intervention introduced. Performing a cost-effective analysis we identify that the same strategy also proves to be efficacious and cost-effective. Finally, we suggest that our model would be helpful for policy makers to predict the best intervention strategies for specific time periods and their appropriate implementation for elimination of visceral leishmaniasis.
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Affiliation(s)
- Santanu Biswas
- Department of Mathematics, Adamas University, Barasat, Kolkata, India
| | - Abhishek Subramanian
- Chemical Engineering and Process Development, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune, 411008, India
- Academy of Scientific & Innovative Research (AcSIR), CSIR-NCL Campus, Pune - 411008, India
| | - Ibrahim M. ELMojtaba
- Department of Mathematics and Statistics, College of Science - Sultan Qaboos University, P.O. box - 36, Muscat, Oman
| | - Joydev Chattopadhyay
- Agricultural and Ecological Research Unit, Indian Statistical Institute, 203, B. T. Road, Kolkata, 700108, India
| | - Ram Rup Sarkar
- Chemical Engineering and Process Development, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune, 411008, India
- Academy of Scientific & Innovative Research (AcSIR), CSIR-NCL Campus, Pune - 411008, India
- * E-mail:
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16
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Das VNR, Pandey RN, Siddiqui NA, Chapman LAC, Kumar V, Pandey K, Matlashewski G, Das P. Longitudinal Study of Transmission in Households with Visceral Leishmaniasis, Asymptomatic Infections and PKDL in Highly Endemic Villages in Bihar, India. PLoS Negl Trop Dis 2016; 10:e0005196. [PMID: 27974858 PMCID: PMC5156552 DOI: 10.1371/journal.pntd.0005196] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 11/17/2016] [Indexed: 12/13/2022] Open
Abstract
Background Visceral Leishmaniasis (VL) is a neglected tropical disease that afflicts some of the poorest populations in the world including people living in the Bihar state of India. Due to efforts from local governments, NGOs and international organizations, the number of VL cases has declined in recent years. Despite this progress, the reservoir for transmission remains to be clearly defined since it is unknown what role post kala-azar dermal leishmaniasis (PKDL) and asymptomatic infections play in transmission. This information is vital to establish effective surveillance and monitoring to sustainably eliminate VL. Methodology/Principal Findings We performed a longitudinal study over a 24-month period to examine VL transmission and seroconversion in households with VL, PKDL and asymptomatic infections in the Saran and Muzaffarpur districts of Bihar. During the initial screening of 5,144 people in 16 highly endemic villages, 195 cases of recently treated VL, 116 healthy rK39 positive cases and 31 PKDL cases were identified. Approximately half of the rK39-positive healthy cases identified during the initial 6-month screening period were from households (HHs) where a VL case had been identified. During the 18-month follow-up period, seroconversion of family members in the HHs with VL cases, PKDL cases, and rK39-positive individuals was similar to control HHs. Therefore, seroconversion was highest in HHs closest to the time of VL disease of a household member and there was no evidence of higher transmission in households with PKDL or healthy rK39-positive HHs. Moreover, within the PKDL HHs, (the initial 31 PKDL cases plus an additional 66 PKDL cases), there were no cases of VL identified during the initial screen or the 18-month follow-up. Notably, 23% of the PKDL cases had no prior history of VL suggesting that infection resulting directly in PKDL is more common than previously estimated. Conclusions/Significance These observations argue that acute VL cases represent the major reservoir for transmission in these villages and early identification and treatment of VL cases should remain a priority for VL elimination. We were unable to obtain evidence that transmission occurs in HHs with a PKDL case. Visceral leishmaniasis (also known as kala-azar) caused by infection with L. donovani is a deadly parasitic disease that afflicts some of world’s poorest populations, including the people of the northern Bihar State of India. Once transmitted to a human by an infected sandfly, the L. donovani parasite migrates from the site of the sandfly bite throughout the reticuloendothelial system, resulting in high levels of infection in the spleen, liver and bone marrow that eventually lead to organ failure and death if not treated effectively. India, Nepal and Bangladesh are currently engaged in a program to eliminate visceral leishmaniasis, principally through early case detection, treatment and vector control. As humans are the only reservoir for L. donovani, it is necessary to understand how the disease is transmitted and specifically what role acute visceral leishmaniasis (VL) cases, asymptomatic infections and post kala-azar dermal leishmaniasis (PKDL) cases play in transmission. We therefore performed a study to determine seroconversion for antibodies against the L. donovani rK39 antigen as a surrogate for transmission in households with VL cases, asymptomatic infections and PKDL cases in 16 highly endemic villages over a 2-year period in Bihar, India. We observed that most transmission occurred in the VL households and further that it occurred closest to the time of acute disease. We were unable to confirm that transmission occurred in the households with either asymptomatic infections or PKDL cases. These observations argue that active surveillance to diagnose and treat VL cases as soon as possible to reduce transmission should remain a priority for VL elimination.
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Affiliation(s)
- Vidya Nand Ravi Das
- Rajendra Memorial Research Institute of Medical Sciences (ICMR), Patna, India
| | | | | | | | - Vijay Kumar
- Rajendra Memorial Research Institute of Medical Sciences (ICMR), Patna, India
| | - Krishna Pandey
- Rajendra Memorial Research Institute of Medical Sciences (ICMR), Patna, India
| | - Greg Matlashewski
- Department of Microbiology and Immunology, McGill University, Montreal, Quebec, Canada
- * E-mail: (PD); (GM)
| | - Pradeep Das
- Rajendra Memorial Research Institute of Medical Sciences (ICMR), Patna, India
- * E-mail: (PD); (GM)
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17
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Rock KS, Quinnell RJ, Medley GF, Courtenay O. Progress in the Mathematical Modelling of Visceral Leishmaniasis. ADVANCES IN PARASITOLOGY 2016; 94:49-131. [PMID: 27756459 DOI: 10.1016/bs.apar.2016.08.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The leishmaniases comprise a complex of diseases characterized by clinical outcomes that range from self-limiting to chronic, and disfiguring and stigmatizing to life threatening. Diagnostic methods, treatments, and vector and reservoir control options exist, but deciding the most effective interventions requires a quantitative understanding of the population level infection and disease dynamics. The effectiveness of any set of interventions has to be determined within the context of operational conditions, including economic and political commitment. Mathematical models are the best available tools for studying quantitative systems crossing disciplinary spheres (biology, medicine, economics) within environmental and societal constraints. In 2005, the World Health Assembly and government health ministers of India, Nepal, and Bangladesh signed a Memorandum of Understanding to eliminate the life threatening form of leishmaniasis, visceral leishmaniasis (VL), on the Indian subcontinent by 2015 through a combination of early case detection, improved treatments, and vector control. The elimination target is <1 case/10,000 population at the district or subdistrict level compared to the current 20/10,000 in the regions of highest transmission. Towards this goal, this chapter focuses on mathematical models of VL, and the biology driving those models, to enable realistic predictions of the best combination of interventions. Several key issues will be discussed which have affected previous modelling of VL and the direction future modelling may take. Current understanding of the natural history of disease, immunity (and loss of immunity), and stages of infection and their durations are considered particularly for humans, and also for dogs. Asymptomatic and clinical infection are discussed in the context of their relative roles in Leishmania transmission, as well as key components of the parasite-sandfly-vector interaction and intervention strategies including diagnosis, treatment and vector control. Gaps in current biological knowledge and potential avenues to improve model structures and mathematical predictions are identified. Underpinning the marriage between biology and mathematical modelling, the content of this chapter represents the first step towards developing the next generation of models for VL.
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Affiliation(s)
- K S Rock
- University of Warwick, Coventry, United Kingdom
| | | | - G F Medley
- London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - O Courtenay
- University of Warwick, Coventry, United Kingdom
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Abstract
At the beginning of the new millennium, helminth infections continue to be prevalent, particularly among impoverished populations. This study attempts to create the first health informatics model of helminthiasis in Thailand. The authors investigate how a health informatics model could be used to predict the control and eradication in a national control campaign. Fish-borne helminthiasis caused by Opisthorchis viverrini remains a major public health problem in many parts of South-East Asia, including Thailand, Lao PDR, Vietnam and Cambodia. The epicentre of this disease is located in north-east Thailand, where high prevalence coexists with a high incidence of cholangiocarcinoma (CHCA). The current report was conducted to determine a mathematical model of surveillance for helminthiasis while also using a geographic information system. The fish-borne helminthiasis model or the predicted equation was Y1 = 3.028 + 0.020 (elevation) - 2.098 (clay). For soil-transmitted helminthiasis, the mathematical model or the predicted equation was Y2 = -1.559 + 0.005 (rainfall) + 0.004 (elevation) - 2.198 (clay). The Ministry of Public Health has concluded that mass treatment for helminthiasis in the Thai population, targeting high-risk individuals, may be a cost-effective way to allocate limited funds. This type of approach, as well as further study on the correlation of clinical symptoms with environmental and geographic information, may offer a novel strategy to the helminth crisis.
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Transmission Dynamics of Visceral Leishmaniasis in the Indian Subcontinent - A Systematic Literature Review. PLoS Negl Trop Dis 2016; 10:e0004896. [PMID: 27490264 PMCID: PMC4973965 DOI: 10.1371/journal.pntd.0004896] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 07/12/2016] [Indexed: 12/24/2022] Open
Abstract
Background As Bangladesh, India and Nepal progress towards visceral leishmaniasis (VL) elimination, it is important to understand the role of asymptomatic Leishmania infection (ALI), VL treatment relapse and post kala-azar dermal leishmaniasis (PKDL) in transmission. Methodology/ Principal Finding We reviewed evidence systematically on ALI, relapse and PKDL. We searched multiple databases to include studies on burden, risk factors, biomarkers, natural history, and infectiveness of ALI, PKDL and relapse. After screening 292 papers, 98 were included covering the years 1942 through 2016. ALI, PKDL and relapse studies lacked a reference standard and appropriate biomarker. The prevalence of ALI was 4–17-fold that of VL. The risk of ALI was higher in VL case contacts. Most infections remained asymptomatic or resolved spontaneously. The proportion of ALI that progressed to VL disease within a year was 1.5–23%, and was higher amongst those with high antibody titres. The natural history of PKDL showed variability; 3.8–28.6% had no past history of VL treatment. The infectiveness of PKDL was 32–53%. The risk of VL relapse was higher with HIV co-infection. Modelling studies predicted a range of scenarios. One model predicted VL elimination was unlikely in the long term with early diagnosis. Another model estimated that ALI contributed to 82% of the overall transmission, VL to 10% and PKDL to 8%. Another model predicted that VL cases were the main driver for transmission. Different models predicted VL elimination if the sandfly density was reduced by 67% by killing the sandfly or by 79% by reducing their breeding sites, or with 4–6y of optimal IRS or 10y of sub-optimal IRS and only in low endemic setting. Conclusion/ Significance There is a need for xenodiagnostic and longitudinal studies to understand the potential of ALI and PKDL as reservoirs of infection. The role of asymptomatic Leishmania infection (ALI), PKDL and VL relapse in transmission is unclear as VL elimination is achieved in the Indian subcontinent. ALI, PKDL and relapse studies lacked a reference standard and appropriate biomarker. ALI was 4–17-fold more prevalent than VL. The risk of ALI was higher in VL case contacts. Most infections remained asymptomatic or resolved spontaneously. The natural history of PKDL showed variability. Twenty nine percent had no past history of VL treatment. The risk of VL relapse was higher with HIV co-infection. Modelling studies predicted different effects. Early diagnosis was unlikely to eliminate VL in the long term. ALI was predicted to contribute to 82% of the overall transmission, VL to 10% and PKDL to 8%. Another model predicted that VL cases were the main driver for transmission. VL elimination was predicted if the sandfly density was reduced by 67% by killing the sandfly or by 79% by reducing their breeding sites, or with 4–6y of optimal IRS or 10y of sub-optimal IRS and only in low endemic setting. There is a need for more studies to fully understand the potential of ALI and PKDL as reservoirs of infection.
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20
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Petitdidier E, Pagniez J, Papierok G, Vincendeau P, Lemesre JL, Bras-Gonçalves R. Recombinant Forms of Leishmania amazonensis Excreted/Secreted Promastigote Surface Antigen (PSA) Induce Protective Immune Responses in Dogs. PLoS Negl Trop Dis 2016; 10:e0004614. [PMID: 27223609 PMCID: PMC4880307 DOI: 10.1371/journal.pntd.0004614] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 03/16/2016] [Indexed: 01/08/2023] Open
Abstract
Preventive vaccination is a highly promising strategy for interrupting leishmaniasis transmission that can, additionally, contribute to elimination. A vaccine formulation based on naturally excreted secreted (ES) antigens was prepared from L. infantum promastigote culture supernatant. This vaccine achieved successful results in Phase III trials and was licensed and marketed as CaniLeish. We recently showed that newly identified ES promastigote surface antigen (PSA), from both viable promastigotes and axenically-grown amastigotes, represented the major constituent and the highly immunogenic antigen of L. infantum and L. amazonensis ES products. We report here that three immunizations with either the recombinant ES LaPSA-38S (rPSA) or its carboxy terminal part LaPSA-12S (Cter-rPSA), combined with QA-21 as adjuvant, confer high levels of protection in naive L. infantum-infected Beagle dogs, as checked by bone marrow parasite absence in respectively 78.8% and 80% of vaccinated dogs at 6 months post-challenge. The parasite burden in infected vaccinated dogs was significantly reduced compared to placebo group, as measured by q-PCR. Moreover, our results reveal humoral and cellular immune response clear-cut differences between vaccinated and control dogs. An early increase in specific IgG2 antibodies was observed in rPSA/QA-21- and Cter-rPSA/QA-21-immunized dogs only. They were found functionally active in vitro and were highly correlated with vaccine protection. In vaccinated protected dogs, IFN-γ and NO productions, as well as anti-leishmanial macrophage activity, were increased. These data strongly suggest that ES PSA or its carboxy-terminal part, in recombinant forms, induce protection in a canine model of zoonotic visceral leishmaniasis by inducing a Th1-dominant immune response and an appropriate specific antibody response. These data suggest that they could be considered as important active components in vaccine candidates. Visceral leishmaniasis (VL), a potentially fatal disease caused by L. infantum, represents perfectly the need for a “One Health” approach for disease control, since it affects both humans and dogs, with similar clinical outcome and T-cell mediated immunity commitment. The dog vaccine development is highly required as our present resources for VL treatment and control have a limited effectiveness. It would represent the most convenient and efficient control way to decrease the dog-sandfly-dog transmission cycle, essential for human incidence reduction. The results indicate that recombinant forms of soluble promastigote surface antigen (PSA) are very promising effective vaccine candidates against canine VL. The elicited immune responses effectively reduced parasite load in in vitro pre-infected macrophages and in experimentally infected dogs. Through this approach, we aim to reduce the number of infected animals developing progressive infections thereby positively influencing human public health.
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MESH Headings
- Adaptive Immunity
- Adjuvants, Immunologic
- Animals
- Antibodies, Protozoan/blood
- Antigens, Protozoan/genetics
- Antigens, Protozoan/immunology
- Antigens, Surface/genetics
- Antigens, Surface/immunology
- Bone Marrow/parasitology
- Disease Models, Animal
- Dog Diseases/immunology
- Dog Diseases/parasitology
- Dog Diseases/prevention & control
- Dogs
- Female
- Immunity, Cellular
- Immunoglobulin G/blood
- Interferon-gamma/biosynthesis
- Leishmania infantum/immunology
- Leishmania infantum/physiology
- Leishmania mexicana/chemistry
- Leishmania mexicana/genetics
- Leishmania mexicana/immunology
- Leishmaniasis Vaccines/administration & dosage
- Leishmaniasis Vaccines/genetics
- Leishmaniasis Vaccines/immunology
- Leishmaniasis, Visceral/immunology
- Leishmaniasis, Visceral/parasitology
- Leishmaniasis, Visceral/prevention & control
- Leishmaniasis, Visceral/veterinary
- Macrophages/immunology
- Nitric Oxide/biosynthesis
- Parasite Load
- Polymerase Chain Reaction
- Protozoan Proteins/genetics
- Protozoan Proteins/immunology
- Recombinant Proteins/administration & dosage
- Recombinant Proteins/immunology
- Th1 Cells/immunology
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Affiliation(s)
| | - Julie Pagniez
- IRD, UMR 177 INTERTRYP IRD CIRAD, Montpellier, France
| | | | - Philippe Vincendeau
- University Hospital of Bordeaux, Laboratoire de Parasitologie-Mycologie, Bordeaux, France
- Université de Bordeaux, UMR 177 INTERTRYP IRD CIRAD, Bordeaux, France
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Cameron MM, Acosta-Serrano A, Bern C, Boelaert M, den Boer M, Burza S, Chapman LAC, Chaskopoulou A, Coleman M, Courtenay O, Croft S, Das P, Dilger E, Foster G, Garlapati R, Haines L, Harris A, Hemingway J, Hollingsworth TD, Jervis S, Medley G, Miles M, Paine M, Picado A, Poché R, Ready P, Rogers M, Rowland M, Sundar S, de Vlas SJ, Weetman D. Understanding the transmission dynamics of Leishmania donovani to provide robust evidence for interventions to eliminate visceral leishmaniasis in Bihar, India. Parasit Vectors 2016; 9:25. [PMID: 26812963 PMCID: PMC4729074 DOI: 10.1186/s13071-016-1309-8] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 01/15/2016] [Indexed: 12/31/2022] Open
Abstract
Visceral Leishmaniasis (VL) is a neglected vector-borne disease. In India, it is transmitted to humans by Leishmania donovani-infected Phlebotomus argentipes sand flies. In 2005, VL was targeted for elimination by the governments of India, Nepal and Bangladesh by 2015. The elimination strategy consists of rapid case detection, treatment of VL cases and vector control using indoor residual spraying (IRS). However, to achieve sustained elimination of VL, an appropriate post elimination surveillance programme should be designed, and crucial knowledge gaps in vector bionomics, human infection and transmission need to be addressed. This review examines the outstanding knowledge gaps, specifically in the context of Bihar State, India.The knowledge gaps in vector bionomics that will be of immediate benefit to current control operations include better estimates of human biting rates and natural infection rates of P. argentipes, with L. donovani, and how these vary spatially, temporally and in response to IRS. The relative importance of indoor and outdoor transmission, and how P. argentipes disperse, are also unknown. With respect to human transmission it is important to use a range of diagnostic tools to distinguish individuals in endemic communities into those who: 1) are to going to progress to clinical VL, 2) are immune/refractory to infection and 3) have had past exposure to sand flies.It is crucial to keep in mind that close to elimination, and post-elimination, VL cases will become infrequent, so it is vital to define what the surveillance programme should target and how it should be designed to prevent resurgence. Therefore, a better understanding of the transmission dynamics of VL, in particular of how rates of infection in humans and sand flies vary as functions of each other, is required to guide VL elimination efforts and ensure sustained elimination in the Indian subcontinent. By collecting contemporary entomological and human data in the same geographical locations, more precise epidemiological models can be produced. The suite of data collected can also be used to inform the national programme if supplementary vector control tools, in addition to IRS, are required to address the issues of people sleeping outside.
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Affiliation(s)
- Mary M Cameron
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | | | - Caryn Bern
- UCSF School of Medicine, 550 16th Street, San Francisco, 94158, CA, USA.
| | | | | | - Sakib Burza
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | | | - Alexandra Chaskopoulou
- European Biological Control Laboratory, USDA-ARS, Tsimiski 43 Street, Thessaloniki, 54623, Greece.
| | - Michael Coleman
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | - Orin Courtenay
- University of Warwick, Gibbet Hill Campus, Coventry, CV4 7AL, UK.
| | - Simon Croft
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | - Pradeep Das
- Rajendra Memorial Research Institute of Medical Sciences, Patna, India.
| | - Erin Dilger
- University of Warwick, Gibbet Hill Campus, Coventry, CV4 7AL, UK.
| | - Geraldine Foster
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | | | - Lee Haines
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | | | - Janet Hemingway
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | | | - Sarah Jervis
- University of Warwick, Gibbet Hill Campus, Coventry, CV4 7AL, UK.
| | - Graham Medley
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | - Michael Miles
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | - Mark Paine
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | - Albert Picado
- FIND, Campus Biotech, Chemin des Mines 9, 1202, Geneva, Switzerland.
| | - Richard Poché
- Genesis Laboratories, Inc., Wellington, CO, 80549, USA.
| | - Paul Ready
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | - Matthew Rogers
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | - Mark Rowland
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
| | - Shyam Sundar
- Institute of Medical Sciences, Banaras Hindu University, Varanasi, 221005, India.
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, Netherlands.
| | - David Weetman
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
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Le Rutte EA, Coffeng LE, Bontje DM, Hasker EC, Postigo JAR, Argaw D, Boelaert MC, De Vlas SJ. Feasibility of eliminating visceral leishmaniasis from the Indian subcontinent: explorations with a set of deterministic age-structured transmission models. Parasit Vectors 2016; 9:24. [PMID: 26787302 PMCID: PMC4717541 DOI: 10.1186/s13071-016-1292-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 12/31/2015] [Indexed: 02/02/2023] Open
Abstract
Background Visceral leishmaniasis (VL) is a neglected tropical disease transmitted by sandflies. On the Indian subcontinent (ISC), VL is targeted for elimination as a public health problem by 2017. In the context of VL, the elimination target is defined as an annual VL incidence of <1 per 10,000 capita at (sub-)district level. Interventions focus on vector control, surveillance and on diagnosing and treating VL cases. Many endemic areas have not yet achieved optimal control due to logistical, biological as well as technical challenges. We used mathematical modelling to quantify VL transmission dynamics and predict the feasibility of achieving the VL elimination target with current control strategies under varying assumptions about the reservoir of infection in humans. Methods We developed three deterministic age-structured transmission models with different main reservoirs of infection in humans: asymptomatic infections (model 1), reactivation of infection after initial infection (model 2), and post kala-azar dermal leishmaniasis (PKDL; model 3). For each model, we defined four sub-variants based on different assumptions about the duration of immunity and age-patterns in exposure to sandflies. All 12 model sub-variants were fitted to data from the KalaNet study in Bihar (India) and Nepal, and the best sub-variant was selected per model. Predictions were made for optimal and sub-optimal indoor residual spraying (IRS) effectiveness for three different levels of VL endemicity. Results Structurally different models explained the KalaNet data equally well. However, the predicted impact of IRS varied substantially between models, such that a conclusion about reaching the VL elimination targets for the ISC heavily depends on assumptions about the main reservoir of infection in humans: asymptomatic cases, recovered (immune) individuals that reactivate, or PKDL cases. Conclusions Available data on the impact of IRS so far suggest one model is probably closest to reality (model 1). According to this model, elimination of VL (incidence of <1 per 10,000) by 2017 is only feasible in low and medium endemic settings with optimal IRS. In highly endemic settings and settings with sub-optimal IRS, additional interventions will be required. Electronic supplementary material The online version of this article (doi:10.1186/s13071-016-1292-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Epke A Le Rutte
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, PO Box 2040, 3000 CA, Rotterdam, The Netherlands.
| | - Luc E Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, PO Box 2040, 3000 CA, Rotterdam, The Netherlands.
| | - Daniel M Bontje
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, PO Box 2040, 3000 CA, Rotterdam, The Netherlands.
| | - Epco C Hasker
- Institute of Tropical Medicine, Nationalestraat 155, 2000, Antwerp, Belgium.
| | | | - Daniel Argaw
- World Health Organization, Avenue Appia 20, 1211, Geneva, Switzerland.
| | - Marleen C Boelaert
- Institute of Tropical Medicine, Nationalestraat 155, 2000, Antwerp, Belgium.
| | - Sake J De Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, PO Box 2040, 3000 CA, Rotterdam, The Netherlands.
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Health-seeking behaviour, diagnostics and transmission dynamics in the control of visceral leishmaniasis in the Indian subcontinent. Nature 2015; 528:S102-8. [PMID: 26633763 DOI: 10.1038/nature16042] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Countries in the Indian subcontinent have committed to reducing the incidence of kala-azar, a clinical manifestation of visceral leishmaniasis, to below 1 in 10,000 by 2020. We address the role of timing of use and accuracy of diagnostics in kala-azar control and elimination. We use empirical data on health-seeking behaviour and health-system performance from the Indian state of Bihar, Bangladesh and Nepal to parameterize a mathematical model. Diagnosis of cases is key to case management, control and surveillance. Treatment of cases prevents onward transmission, and we show that the differences in time to diagnosis in these three settings explain the observed differences in incidence. Shortening the time from health-care seeking to diagnosis is likely to lead to dramatic reductions in incidence in Bihar, bringing the incidence down to the levels seen in Bangladesh and Nepal. The results emphasize the importance of maintaining population and health-system awareness, particularly as transmission and disease incidence decline. We explore the possibility of diagnosing patients before the onset of clinical kala-azar (before 14 days fever), and show that this could have a marked impact on incidence, even for a moderately sensitive test. However, limited specificity (that results in false positives) is a major barrier to such a strategy. Diagnostic tests of high specificity used at an early stage of active infection, even if sensitivity is only moderate, could have a key role in the control of kala-azar, and prevent its resurgence when paired with the passive health-care system and tests of high sensitivity, such as the test for rK39 antibody response.
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Berthier D, Brenière SF, Bras-Gonçalves R, Lemesre JL, Jamonneau V, Solano P, Lejon V, Thévenon S, Bucheton B. Tolerance to Trypanosomatids: A Threat, or a Key for Disease Elimination? Trends Parasitol 2015; 32:157-168. [PMID: 26643519 DOI: 10.1016/j.pt.2015.11.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Revised: 10/20/2015] [Accepted: 11/03/2015] [Indexed: 12/20/2022]
Abstract
So far, research on trypanosomatid infections has been driven by 'disease by disease' approaches, leading to different concepts and control strategies. It is, however, increasingly clear that they share common features such as the ability to generate long-lasting asymptomatic infections in their mammalian hosts. Trypanotolerance, long integrated in animal African trypanosomiasis control, historically refers to the ability of cattle breeds to limit Trypanosoma infection and pathology, but has only recently been recognized in humans. Whilst trypanotolerance is absent from the vocabulary on leishmaniasis and Chagas disease, asymptomatic infections also occur. We review the concept of trypanotolerance across the trypanosomatids and discuss the importance of asymptomatic carriage in the current context of elimination.
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Affiliation(s)
| | | | | | | | - Vincent Jamonneau
- CIRDES Bobo-Dioulasso 01 BP 454, Burkina Faso; IPR, 01 BP 1500 Bouaké 01, Côte d'Ivoire
| | | | - Veerle Lejon
- IRD, UMR INTERTRYP, Montpellier Cedex 5, 34398 France
| | | | - Bruno Bucheton
- IRD, UMR INTERTRYP, Montpellier Cedex 5, 34398 France; PNLTHA, Ministère de la Santé, BP 851 Conakry, République de Guinée
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Chapman LAC, Dyson L, Courtenay O, Chowdhury R, Bern C, Medley GF, Hollingsworth TD. Quantification of the natural history of visceral leishmaniasis and consequences for control. Parasit Vectors 2015; 8:521. [PMID: 26490668 PMCID: PMC4618734 DOI: 10.1186/s13071-015-1136-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 10/03/2015] [Indexed: 01/20/2023] Open
Abstract
Background Visceral leishmaniasis has been targeted for elimination as a public health problem (less than 1 case per 10,000 people per year) in the Indian sub-continent by 2017. However, there is still a high degree of uncertainty about the natural history of the disease, in particular about the duration of asymptomatic infection and the proportion of asymptomatically infected individuals that develop clinical visceral leishmaniasis. Quantifying these aspects of the disease is key for guiding efforts to eliminate visceral leishmaniasis and maintaining elimination once it is reached. Methods Data from a detailed epidemiological study in Bangladesh in 2002–2004 was analysed to estimate key epidemiological parameters. The role of diagnostics in determining the probability and rate of progression to clinical disease was estimated by fitting Cox proportional hazards models. A multi-state Markov model of the natural history of visceral leishmaniasis was fitted to the data to estimate the asymptomatic infection period and the proportion of asymptomatic individuals going on to develop clinical symptoms. Results At the time of the study, individuals were taking several months to be diagnosed with visceral leishmaniasis, leading to many opportunities for ongoing transmission. The probability of progression to clinical disease was strongly associated with initial seropositivity and even more strongly with seroconversion, with most clinical symptoms developing within a year. The estimated average durations of asymptomatic infection and symptomatic infection for our model of the natural history are 147 days (95 % CI 130–166) and 140 days (95 % CI 123–160), respectively, and are significantly longer than previously reported estimates. We estimate from the data that 14.7 % (95 % CI 12.6-20.0 %) of asymptomatic individuals develop clinical symptoms—a greater proportion than previously estimated. Conclusions Extended periods of asymptomatic infection could be important for visceral leishmaniasis transmission, but this depends critically on the relative infectivity of asymptomatic and symptomatic individuals to sandflies. These estimates could be informed by similar analysis of other datasets. Our results highlight the importance of reducing times from onset of symptoms to diagnosis and treatment to reduce opportunities for transmission. Electronic supplementary material The online version of this article (doi:10.1186/s13071-015-1136-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Lloyd A C Chapman
- School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, CV4 7AL, UK.
| | - Louise Dyson
- School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, CV4 7AL, UK
| | - Orin Courtenay
- School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry, CV4 7AL, UK
| | - Rajib Chowdhury
- Country Programme Manager - Bangladesh, KalaCORE Programme, Dhaka, Bangladesh.,Department of Medical Entomology, National Institute of Preventive and Social Medicine (NIPSOM), Mohakhali, Dhaka, Bangladesh
| | - Caryn Bern
- UCSF School of Medicine, 550 16th Street, San Francisco, CA, 94158, USA
| | - Graham F Medley
- London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK
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