Residual malaria transmission in Western Burkina Faso: Vector Behavior, insecticide resistance, and the efficacy limits of next-generation LLINs.

An entomological surveillance was carried out in two districts of western Burkina Faso to assess the impact of mass-distributed next-generation long-lasting insecticidal nets (LLINs) (Piperonyl Butoxide (PBO) LLINs and Interceptor® G2) on Anopheles gambiae s.l. populations, focusing on insecticide resistance trends and residual malaria transmission patterns, along with their environmental and operational determinants. Hourly indoor and outdoor mosquito collections were conducted across four households per district form August-October 2023 using Human Landing Catch and Pyrethrum Spray Catch. All collected mosquitoes were morphologically identified. Molecular analysis was performed on Anopheles gambiae s.l. to determine species composition, blood meal sources, Plasmodium falciparum infection rates, and insecticide resistance mutations. Seven Anopheles species were recorded, with the An. gambiae s.l. complex being predominant. Species composition varied significantly by month (August-October), with An. coluzzii being the dominant species, followed by An. arabiensis. Early and late biting behaviors were observed among vector populations. Entomological inoculation rates were 0.875, 0.437, and 0.063 infectious bites/person/month in August, September, and October, respectively. Kdr-west and kdr-east mutations were detected across all members of the An. gambiae s.l. complex, though at varying frequencies. This study highlights the diversity and behavioral adaptability of the Anopheles gambiae s.l. complex. Despite widespread use of LLINs and indoor residual spraying (IRS), substantial residual malaria transmission persists. These findings offer critical evidence for optimizing vector control and resistance management strategies in Burkina Faso.