Nationwide cross-sectional surveillance of Leishmania donovani in phlebotomine sand flies and its impact on national kala-azar elimination in India

Abstract

India is accelerating efforts to eliminate kala-azar by aligning its National Kala-Azar Elimination Program with the World Health Organization's (WHO) roadmap for Neglected Tropical Diseases (NTDs) 2021-2030. Elimination relies on comprehensive vector surveillance and integrated vector management. This study aimed to conduct nationwide entomological surveillance to detect Leishmania donovani in phlebotomine sand flies. A cross-sectional survey was conducted from January 2022 to December 2023 in five different biogeographical zones in India. Mechanical aspirator, light traps were used for sampling. The collected sand flies were identified to species level. Molecular xenomonitoring was conducted using kDNA qPCR, and parasite characterization targeting ITS1 gene sequencing and RFLP. Sand fly species was confirmed by DNA barcode. Molecular xenomonitoring revealed that Phlebotomus argentipes from Bihar, West Bengal, and Kerala exhibited high levels of L. donovani parasitic DNA. In Rajasthan, P. sergenti and P. papatasi and in Himachal Pradesh, P. longiductus, P. major, and P. bruneyi were positive. The high levels of L. donovani parasitic DNA detected in various Phlebotomus species, along with its presence in other sand fly species beyond the established vectors, underscore the urgent need for the National Kala-Azar Elimination Program to prioritize comprehensive and rigorous vector surveillance. Strengthening these efforts is crucial for achieving the program's goal of eliminating the disease.