Monitoring of Leishmania transmission in the post-elimination phase: the potential of serological surveys.

OBJECTIVES: Monitoring of Leishmania transmission is considered a strategic priority for sustaining elimination of visceral leishmaniasis as a public health problem in the Indian subcontinent. The objective of this study was to evaluate whether serological surveys can distinguish between communities with and without Leishmania transmission, and to assess which serological marker performs best. METHODS: Seven villages were selected from Bihar and Uttar Pradesh state, India, and categorized as either currently endemic, previously endemic or non-endemic. Blood samples were analyzed with the rK39 RDT, DAT, and rK39 ELISA. RESULTS: Contrary to the rK39 RDT and DAT, the rK39 ELISA showed a significant difference between all three categories of endemicity, with a seroprevalence of 5.21% in currently endemic villages, 1.55% in previously endemic villages, and 0.13% in non-endemic villages. Even when only looking at the seroprevalence among children aged <10 years, the rK39 ELISA was still able to differentiate between villages with and without ongoing transmission. CONCLUSIONS: Our findings suggest the rK39 ELISA to be the most promising marker for monitoring of Leishmania transmission. Further validation is required, and practical, context-adapted recommendations need to be formulated in order to guide policy makers towards meaningful and sustainable surveillance strategies in the post-elimination phase.

Wuchereria bancrofti infection is associated with progression to clinical visceral leishmaniasis in VL- endemic areas in Muzaffarpur, Bihar, India.

BACKGROUND: Co-endemicity of neglected tropical diseases (NTDs) necessitates that these diseases should be considered concomitantly to understand the relationship between pathology and to support disease management and control programs. The aims of the study were to assess the prevalence of filarial infection in asymptomatic Leishmania donovani infected individuals and the correlation of Wuchereria bancrofti infection with progression to clinical visceral leishmaniasis (VL) in Bihar, India. METHODOLOGY/PRINCIPAL FINDINGS: Within the Muzaffarpur-TMRC Health and Demographic Surveillance System (HDSS) area, a cohort of Leishmania seropositive (n = 476) or seronegative individuals (n = 1130) were sampled annually for three years for filarial infection and followed for progression to clinical VL. To corroborate the results from the cohort study, we also used a retrospective case-control study of 36 VL cases and 71 controls selected from a subset of the HDSS population to investigate the relationship between progression to clinical VL and the prevalence of filarial infection at baseline. Our findings suggest a higher probability of progression to clinical VL in individuals with a history of filarial infection: in both the cohort and case-control studies, progression to clinical VL was higher among filaria infected individuals (RR = 2.57, p = 0.056, and OR = 2.52, p = 0.046 respectively). CONCLUSION: This study describes that progression to clinical VL disease is associated with serological evidence of prior infection with W. bancrofti. The integration of disease programs for Leishmania and lymphatic filariasis extend beyond the relationship of sequential or co-infection with disease burden. To ensure elimination targets can be reached and sustained, we suggest areas of co-endemicity would benefit from overlapping vector control activities, health system networks and surveillance infrastructure.