Abstract
There is increasing interest in the role of asymptomatic infection in transmission of Visceral Leishmaniasis (VL). We studied the individual, household and environmental factors associated with asymptomatic Leishmania donovani infected individuals and VL. 7,538 individuals living in VL endemic villages in India and Nepal were divided into three mutually exclusive groups based on their VL history and Direct Agglutination Test (DAT) results in yearly serosurveys over a two-year period. The groups were (1) VL cases, (2) asymptomatically infected individuals (seroconverters) and (3) seronegative individuals. VL cases and seroconverters were compared to seronegative individuals in mixed logistic regression models. The risk of seroconversion and disease was significantly increased in individuals aged 14 to 24 years old and by the presence of other DAT-positive, asymptomatically infected individuals and VL cases in the house. The risk of seroconversion was higher in Indian than in Nepalese villages and it increased significantly with age, but not so for VL. This study demonstrates that, when risk factors for leishmanial infection and VL disease are evaluated in the same population, epidemiological determinants for asymptomatic infection and VL are largely similar.
Highlights
Visceral Leishmaniasis (VL), known as kala azar, is one of the major public health concerns in large parts of north-east India, south-eastern Nepal and western Bangladesh
Study Areas and Study Population The subjects included in this study were selected from a large cohort of individuals followed for 2.5 years as part of a cluster randomised controlled trial to evaluate the effect of longlasting insecticidal nets (LN) to prevent L. donovani infection and clinical VL in India and Nepal [18]
The risk factors associated with asymptomatic infection and clinical disease in VL endemic communities in India and Nepal were similar in this prospective cohort with 2.5 years follow-up
Summary
Visceral Leishmaniasis (VL), known as kala azar, is one of the major public health concerns in large parts of north-east India, south-eastern Nepal and western Bangladesh. In 2010 over 28,000 new cases were reported in these three countries [1]. This figure is an underestimation of the real number of cases [2] and falls far from the objective set by the regional governments to eliminate VL from the Indian subcontinent by 2015. Part of the infected individuals eventually develop the disease [5]. Asymptomatic L. donovani infected individuals may play an important role in sustaining transmission in endemic communities as suggested by mathematical modelling [6]. Knowing the factors associated with L. donovani infection and progression to disease could help designing more efficient control strategies
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