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The role of case proximity in transmission of visceral leishmaniasis in a highly endemic village in Bangladesh
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Chapman, Lloyd A. C., Jewell, Chris P., Spencer, Simon E. F., Pellis, Lorenzo, Datta, Samik, Chowdhury, Rajib, Bern, Caryn, Medley, Graham and Hollingsworth, T. Déirdre (2018) The role of case proximity in transmission of visceral leishmaniasis in a highly endemic village in Bangladesh. PLoS Neglected Tropical Diseases, 12 (10). e0006453. doi:10.1371/journal.pntd.0006453 ISSN 1935-2727.
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Official URL: https://doi.org/10.1371/journal.pntd.0006453
Abstract
Background
Visceral leishmaniasis (VL) is characterised by a high degree of spatial clustering at all scales, and this feature remains even with successful control measures. VL is targeted for elimination as a public health problem in the Indian subcontinent by 2020, and incidence has been falling rapidly since 2011. Current control is based on early diagnosis and treatment of clinical cases, and blanket indoor residual spraying of insecticide (IRS) in endemic villages to kill the sandfly vectors. Spatially targeting active case detection and/or IRS to higher risk areas would greatly reduce costs of control, but its effectiveness as a control strategy is unknown. The effectiveness depends on two key unknowns: how quickly transmission risk decreases with distance from a VL case and how much asymptomatically infected individuals contribute to transmission.
Methodology/Principal findings
To estimate these key parameters, a spatiotemporal transmission model for VL was developed and fitted to geo-located epidemiological data on 2494 individuals from a highly endemic village in Mymensingh, Bangladesh. A Bayesian inference framework that could account for the unknown infection times of the VL cases, and missing symptom onset and recovery times, was developed to perform the parameter estimation. The parameter estimates obtained suggest that, in a highly endemic setting, VL risk decreases relatively quickly with distance from a case—halving within 90m—and that VL cases contribute significantly more to transmission than asymptomatic individuals.
Conclusions/Significance
These results suggest that spatially-targeted interventions may be effective for limiting transmission. However, the extent to which spatial transmission patterns and the asymptomatic contribution vary with VL endemicity and over time is uncertain. In any event, interventions would need to be performed promptly and in a large radius (≥300m) around a new case to reduce transmission risk.
Author summary
Visceral leishmaniasis (VL), a fatal parasitic disease transmitted by sandflies, has been targeted for elimination as a public health problem in the Indian subcontinent by 2020. The goal has been reached in the majority of endemic regions in Bangladesh, India and Nepal, but the disease persists in several hotspots. Better understanding of spatial clustering of VL cases and the role of asymptomatically infected individuals in transmission is required to improve control interventions and sustain the elimination target. To address this issue, we have fitted an individual-level spatiotemporal model of VL transmission to geo-located incidence data from Bangladesh to estimate the rate at which VL risk decreases with distance from a case and the potential contribution of asymptomatic individuals to transmission. Our results suggest that VL risk decreases quickly with distance and that symptomatic individuals are the main drivers of transmission, highlighting the potential for spatially-targeted control interventions to reduce transmission.
Item Type: | Journal Article | ||||||
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Subjects: | R Medicine > RC Internal medicine | ||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Life Sciences (2010- ) Faculty of Science, Engineering and Medicine > Science > Statistics |
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Library of Congress Subject Headings (LCSH): | Kala-azar -- Transmission -- Mathematical models , Bayesian statistical decision theory, Public health -- Bangladesh | ||||||
Journal or Publication Title: | PLoS Neglected Tropical Diseases | ||||||
Publisher: | Public Library of Science | ||||||
ISSN: | 1935-2727 | ||||||
Official Date: | 8 October 2018 | ||||||
Dates: |
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Volume: | 12 | ||||||
Number: | 10 | ||||||
Article Number: | e0006453 | ||||||
DOI: | 10.1371/journal.pntd.0006453 | ||||||
Status: | Peer Reviewed | ||||||
Publication Status: | Published | ||||||
Access rights to Published version: | Open Access (Creative Commons) | ||||||
Date of first compliant deposit: | 1 May 2018 | ||||||
Date of first compliant Open Access: | 22 October 2018 | ||||||
RIOXX Funder/Project Grant: |
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