Serological Markers of Sand Fly Exposure to Evaluate Insecticidal Nets against Visceral Leishmaniasis in India and Nepal: A Cluster-Randomized Trial

Visceral leishmaniasis (VL), also known as kala azar, is one of the major public health concerns of the Indian subcontinent, caused by Leishmania donovani transmitted by the bite of the sand fly Phlebotomus argentipes. To date, Indoor Residual Spraying (IRS) campaigns have been unable to control the disease.

This makes Long-lasting insecticidal nets (LNs) an attractive alternative or complement to IRS. Therefore, it is important to assess the extent that LNs reduce bites from P. argentipes. When female sand flies bite they require their saliva to efficiently bloodfeed. For humans and animals alike, the host' immune response against components of sand fly saliva can be used as a marker of exposure to the vector.

Here we describe how comprehensive coverage of LNs in trial communities over two years reduced antibody levels to the saliva of P. argentipes and P. papatasi (a man-biting sand fly that co-exists with P. argentipes but does not transmit VL) sand flies by 9–12% compared to communities without LNs. Our results demonstrate that the large-scale distribution of LNs did not confer significant additional protection against sand fly bites in VL-endemic regions of India and Nepal and questions the indoor transmission of L. donovani in these regions.