Incidence of symptomatic and asymptomatic Leishmania donovani infections in high-endemic foci in India and Nepal: a prospective study

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.

Figure 1. Flowchart of selection process for study population.

Population that was followed up during the Kalanet study covered 21,267 individuals in 26 highly endemic villages in India and Nepal. For the current analysis, only individuals who 1) had no history of Visceral Leishmaniasis 2) were seronegative at baseline (DAT-) and 3) had complete clinical and serological data from baseline to end of the study period = 30 months. DAT = Direct Agglutination Test, cut-off used for positivity was titer ≥1∶1600.

Figure 2. Flowchart of clinical and serological events in study population.

Bars in light grey: Results of the 3 serosurveys IS1 (Immunosurvey 1), IS2 and IS3 that took place in November–December of 2006, 2007 and 2008 respectively. In between the bars: clinical events occurring in between the serosurveys, or in the 6 months following the last serosurvey.