Pyrethroid susceptibility and resistance patterns in Anopheles gambiae populations from Rwanda

Evidence-based vector control interventions depend on understanding the distribution and mechanisms of insecticide resistance in malaria vectors. This study assessed the status of insecticide resistance in Anopheles gambiae sensu lato (s.l.) to pyrethroids, permethrin, deltamethrin, and alphacypermethrin across 18 sites in 15 districts of Rwanda, representing key malaria transmission strata.

Larvae were collected from October 2022 to April 2023 using the dipping method, reared to adulthood, and tested using WHO standard bioassays. Susceptibility profiles were analysed with chi-square tests to compare mortality rates.

There was a high resistance to permethrin in various sites, such as Gashora (42%), Mubuga (48%), Rwaza (69%), and Kirarambogo (70%). Pre-exposure to piperonyl butoxide (PBO) only partially restored susceptibility, with mortality between 70 and 80% at resistant sites. In Kigali city, mortality with alphacypermethrin was 94%, and with PBO, it failed to restore susceptibility, suggesting non-metabolic resistance was involved. Overall, the evidence indicates that metabolic mechanisms play a major role in pyrethroid resistance, though target-site mutations, such as kdr, cannot be ruled out. The reliance on phenotypic data without molecular confirmation remains a limitation, underscoring the need for molecular assays to identify resistance-associated genetic markers.

This study provides essential baseline data on the resistance status of An. gambiae s.l. in Rwanda and highlights the urgent need to integrate molecular tools into routine surveillance to guide more effective vector control strategies.