Abstract
BackgroundStudies performed over the past decade have identified fairly consistent epidemiological patterns of risk factors for visceral leishmaniasis (VL) in the Indian subcontinent.Methods and Principal FindingsTo inform the current regional VL elimination effort and identify key gaps in knowledge, we performed a systematic review of the literature, with a special emphasis on data regarding the role of cattle because primary risk factor studies have yielded apparently contradictory results. Because humans form the sole infection reservoir, clustering of kala-azar cases is a prominent epidemiological feature, both at the household level and on a larger scale. Subclinical infection also tends to show clustering around kala-azar cases. Within villages, areas become saturated over a period of several years; kala-azar incidence then decreases while neighboring areas see increases. More recently, post kala-azar dermal leishmaniasis (PKDL) cases have followed kala-azar peaks. Mud walls, palpable dampness in houses, and peri-domestic vegetation may increase infection risk through enhanced density and prolonged survival of the sand fly vector. Bed net use, sleeping on a cot and indoor residual spraying are generally associated with decreased risk. Poor micronutrient status increases the risk of progression to kala-azar. The presence of cattle is associated with increased risk in some studies and decreased risk in others, reflecting the complexity of the effect of bovines on sand fly abundance, aggregation, feeding behavior and leishmanial infection rates. Poverty is an overarching theme, interacting with individual risk factors on multiple levels.ConclusionsCarefully designed demonstration projects, taking into account the complex web of interconnected risk factors, are needed to provide direct proof of principle for elimination and to identify the most effective maintenance activities to prevent a rapid resurgence when interventions are scaled back. More effective, short-course treatment regimens for PKDL are urgently needed to enable the elimination initiative to succeed.
Highlights
South Asia contains the largest visceral leishmaniasis (VL) focus in the world, with an estimated annual incidence of 200,000– 300,000 clinical cases [1,2]
The disease is caused by the protozoan parasite Leishmania donovani and transmitted by the sand fly Phlebotomus argentipes; infected humans constitute the only demonstrated reservoir [3,4]
To identify risk factor data, we reviewed the literature based on MEDLINE searches using the term visceral leishmaniasis with the subheading risk factors, and the geographic terms India or Bangladesh or Nepal
Summary
South Asia contains the largest visceral leishmaniasis (VL) focus in the world, with an estimated annual incidence of 200,000– 300,000 clinical cases [1,2]. In this region, the disease is caused by the protozoan parasite Leishmania donovani and transmitted by the sand fly Phlebotomus argentipes; infected humans constitute the only demonstrated reservoir [3,4]. In the only published comparative incidence study in South Asia, the ratio of asymptomatic seroconversions to kala-azar cases was 4:1, similar to the 6.5:1 ratio observed in a cohort of Brazilian children [6,7]. Studies performed over the past decade have identified fairly consistent epidemiological patterns of risk factors for visceral leishmaniasis (VL) in the Indian subcontinent
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