Biodiversity, entomological surveillance, and xenomonitoring of sand flies in the Western Ghats, Keralam: an emerging focus of leishmaniasis in India

The Western Ghats of Keralam is a globally recognized biodiversity hotspot, yet information on sand fly (Diptera: Psychodidae) vectors of leishmaniasis from this region remains limited. They play a central role in the transmission of leishmaniasis, a major neglected tropical disease of public health importance in India. This study aimed to generate comprehensive entomological and ecological evidence on sand fly diversity, distribution, and Leishmania infection in the Western Ghats region of Keralam, India. A cross-sectional entomological survey combined with xenomonitoring was conducted between 2021 and 2024 across nine districts of Keralam. Sand flies were collected from indoor, peri-domestic, and outdoor habitats using standard collection methods and analyzed for species composition, habitat preference, seasonal trends, and associations with environmental variables including temperature, rainfall, humidity, and altitude. Biodiversity indices were calculated, and female Phlebotomus argentipes were screened for Leishmania kinetoplast DNA (k-DNA). A total of 12,659 sand flies belonging to 22 species and four genera were collected. Peak abundance was recorded during May–June and September–October. Ph. argentipes was the dominant species, primarily associated with indoor and peri-domestic habitats. Mechanical aspirators yielded higher abundance and species diversity than light traps. Sand fly abundance was positively correlated with relative humidity ( p < 0.001) and negatively correlated with altitude ( p < 0.001), while species diversity declined significantly with increasing elevation ( p = 0.029). The highest diversity was observed in central Keralam (Shannon H’= 2.371; Simpson λ = 0.879) and foothill regions (H’ = 2.328; λ = 0.873). Of 266 Ph. argentipes pools screened, five were positive for Leishmania k-DNA from four districts. This study provides a comprehensive entomological assessment of sand flies in Keralam’s Western Ghats, highlighting species diversity, seasonal patterns, habitat preferences, and Leishmania infection. The findings underscore the need for sustained, evidence-based entomological surveillance to support targeted vector control and advance India’s leishmaniasis elimination efforts.