High Seropositivity to rK39 and Capture of Leishmania-Infected Sand Flies in Bihar and Jharkhand Emphasize the Need for Post-Elimination Surveillance of Visceral Leishmaniasis in India.

Abstract

India is transitioning to the visceral leishmaniasis (VL) post-elimination phase where robust surveillance is critical to sustaining elimination. We conducted a targeted longitudinal study combining epidemiological, serological, and entomological data in endemic villages in Bihar and Jharkhand states to assess active VL transmission levels. Our investigation was conducted in the villages of Rahar Diyara, Bihar, and Murbhanga, Jharkhand, based on spatial distribution of recently reported VL cases. Samples were collected quarterly from December 2021 to September 2022 in Rahar Diyara, and April 2022 to May 2023 in Murbhanga, to determine seroprevalence against Leishmania rK39 antigen. Sand flies were collected bi-weekly in Rahar Diyara (February to December, 2022) and Murbhanga (April to December, 2022) from different microhabitats and analyzed by qPCR targeting Leishmania kDNA. rK39 Leishmania seroprevalence ranged from 20% to 30% in both villages. Murbhanga, an outbreak village, exhibited higher antibody levels in 9-23% of subjects compared with the low incidence village, Rahar Diyara (3-6%), reflecting a higher intensity of transmission in Murbhanga. Despite implementation of indoor residual spraying, Leishmania-infected sand flies were found in both villages, with 1.4% (4/285) and 1.2% (5/431) positive pools in Rahar Diyara and Murbhanga, respectively. Infected sand fly pools were collected from diverse microhabitats, predominantly from vegetation in Rahar Diyara and cattle enclosures in Murbhanga, indicative of focal and distinct patterns of transmission. Low-level Leishmania transmission persists in India highlighting criticality of continued surveillance. Combining epidemiological, serological, and entomological surveys improves rapid outbreak assessment and intervention, and enhances efficacy of surveillance to sustain VL elimination.