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Abstract
Incidence of Leishmania donovani infection and Visceral Leishmaniasis (VL) was assessed in a prospective study in Indian and Nepalese high-endemic villages. DAT-seroconversion was used as marker of incident infection in 3 yearly surveys. The study population was followed up to month 30 to identify incident clinical cases. In a cohort of 9034 DAT-negative individuals with neither active signs nor history of VL at baseline, 42 VL cases and 375 asymptomatic seroconversions were recorded in the first year, giving an infection∶disease ratio of 8.9 to 1. In the 18 months' follow-up, 7 extra cases of VL were observed in the seroconverters group (N = 375), against 14 VL cases among the individuals who had not seroconverted in the first year (N = 8570) (RR = 11.5(4.5<RR<28.3)). Incident asymptomatic L. donovani infection in VL high-endemic foci in India and Nepal is nine times more frequent than incident VL disease. About 1 in 50 of these new but latent infections led to VL within the next 18 months.
Highlights
In the Indian subcontinent 200 million people are estimated to be at risk of developing Visceral Leishmaniasis (VL)
Cross-sectional surveys based on serological testing by Direct Agglutination Test (DAT) [5,6,7,8,9] or ELISA [9] and/or positive delayed-type hypersensitivity (DTH) reaction to a leishmanin skin test (LST) [10,11,12] show high proportions of positive persons who never reported clinical disease
Using DAT seroconversion as a marker of infection, we found incident asymptomatic infection to be nine times more frequent than incident VL disease in high-endemic villages in India and Nepal, and about 1 in 50 of these latent infections lead to VL in the 18 months, while over 80% turn seronegative again within a year
Summary
In the Indian subcontinent 200 million people are estimated to be at risk of developing Visceral Leishmaniasis (VL). Cross-sectional surveys based on serological testing by Direct Agglutination Test (DAT) [5,6,7,8,9] or ELISA [9] and/or positive delayed-type hypersensitivity (DTH) reaction to a leishmanin skin test (LST) [10,11,12] show high proportions of positive persons who never reported clinical disease. It is unclear whether these asymptomatic infected persons are infectious to the sandfly vector, whether they acquire persistent immunity or develop VL later on. Similar estimates are not yet available for India and Nepal, two other countries affected by VL in the Indian subcontinent
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