Effectiveness of Long-lasting Insecticide-Impregnated Bed Nets in Controlling Phlebotomus argentipes in Sri Lanka: A...

Sri Lanka is endemic for cutaneous leishmaniasis (CL) caused by Leishmania donovani. Long-lasting insecticide-impregnated bed nets (LLINs) have been used for vector control, but their impact on interruption of sand fly bites remains untested in Sri Lanka. This study assessed the efficacy of LLINs as compared with untreated bed nets in reducing vector-human contact and density of Phlebotomus argentipes, the vector of CL in Sri Lanka.

A cluster-randomized trial was conducted with an intervention group (treated nets) and a control group (untreated nets) in CL-endemic sites. Blood was collected at baseline and 6 and 12 months to measure antibodies against a P argentipes salivary marker. Sand flies were collected over 32 months with light traps (Centers for Disease Control and Prevention) and cattle-baited traps. Bioassays assessed LLINs' impact on P argentipes mortality, and new CL cases were monitored postintervention.

Postintervention, antibodies against P argentipes salivary marker significantly decreased by 28.8% at 6 months (P = .00002) and 44.9% at 12 months (P = .00001) in the intervention group as compared with the control group. Although indoor and outdoor monthly captures were significantly reduced in the intervention group vs controls, LLINs' impact on reducing P argentipes density was more pronounced indoors, decreasing by 77.3% after 2 months (P = .00001), 89.3% after 10 months (P = .00001), and 63.1% after 24 months (P = .00003). During follow-up, knockdown and Phlebotomus mortality rates ranged from 100% to 81.54% and 100% to 90.43%, respectively. Six CL cases vs 1 case occurred in the control and intervention groups.

LLINs effectively reduced vector exposure and indoor P argentipes density and is a promising intervention for control of CL in Sri Lanka.