Effectiveness of Long-Lasting Insecticide-Impregnated Bed Nets in Controlling Phlebotomus argentipes in Sri Lanka: A Cluster Randomized Controlled Trial.

Background: Sri Lanka is endemic for cutaneous leishmaniasis (CL) caused by Leishmania donovani. Long-lasting insecticide-treated 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 compared to untreated nets in reducing vector-human contact and density of Phlebotomus argentipes, the vector of CL in Sri Lanka.

Methods: A cluster-randomized trial was conducted in intervention (treated nets) and control (untreated nets) groups in CL-endemic sites. Blood was collected at baseline, 6, and 12 months to measure antibodies against a Ph. argentipes salivary marker (PASM). Sand flies were collected over 32 months using CDC light traps and cattle-baited traps. Bioassays assessed LLINs' impact on Ph. argentipes mortality, and new CL cases were monitored post-intervention.

Results: Post-intervention, antibodies against PASM significantly decreased by 28.8% at 6 months (p=0.00002) and 44.9% at 12 months (p=0.00001) in intervention group compared to controls. Though indoor and outdoor monthly captures were significantly reduced in the intervention group compared to controls, LLINs' impact on reducing Ph. argentipes density was more pronounced indoors, decreasing by 77.3% after 2 months (p=0.00001), 89.3% after 10 months (p=0.00001), and 63.1% after 24 months (p=0.00003). During follow-up, knockdown and Phlebotomus mortality rates ranged from 100%-81.54% and 100%-90.43%, respectively. Six CL cases versus one case occurred in control and intervention groups, respectively.

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