Pyrethroid resistance intensity in Anopheles gambiae s.l. mosquito populations from Rwanda
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Evidence based vector control interventions depend on understanding the distribution and the evolution of insecticide resistance in malaria vectors. This study aims to assess the status of insecticide resistance in Anopheles gambiae s.l., to pyrethroid insecticides such as permethrin, deltamethrin, and alphacypermethrin from 18 study sites located in 15 districts across Rwanda, representing the key strata of malaria transmission in the country. The larvae of Anopheles were collected from October 2022 to April 2023 using the dipping method, and reared to the adult stage. The An. gambiae were exposed to alphacypermethrin 0.05% (Acyp_1X), permethrin 0.75% (Perm_1X), and deltamethrin 0.05% (Delth_1X). The susceptibility profile was performed using the WHO bioassay standard protocol for insecticide resistance monitoring and chi-square tests to establish statistical significance between mortality rates. As a result, we found an extremely high resistance to permethrin in Gashora (Bugesera district), Mubuga (Karongi district), Rwaza (Musanze district), Kirarambogo (Gisagara district) with mortality rates of 42%, 48%, 69%, and 70%, repsectively. Subsequently, no recovery of susceptibility was observed in permethrin after pre-exposure to piperonyl butoxide (PBO) and observed mortality was 70% in Kirarambogo, while in Gashora, Mubuga and Rwanza it was 80% at each site. In the city of Kigali, the mortality with alphacypermethrin was 94% and 93% with synergist PBO. Notably, in Kicukiro district we found that the metabolic resistance mechanism was not driving the resistance mechanisms. These findings provide important understandings of pyrethroid resistance status in Rwanda and offer valuable insights for distribution of insecticide resistance intensity across the country. This highlights the need for further studies to assess the spread of insecticide resistance and molecular driven resistance mechanisms to address the issue of malaria vector control in Rwanda.
