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The response to recent dengue outbreaks in Burkina Faso was insecticide-based, despite poor knowledge of the vector population's susceptibility to the insecticides used. Here, we report on the susceptibility to the main insecticide classes and identify important underlying mechanisms in Aedes aegypti populations in Ouagadougou and Banfora, in 2019 and 2020. Wild Ae. aegypti were tested as adults in WHO bioassays and then screened in real time melting curve qPCR analyses to genotype the F1534C, V1016I, and V410L Aedes kdr mutations. Ae. aegypti showed moderate resistance to 0.1% bendiocarb (80-95% survival post-exposure), 0.8% Malathion (60-100%), 0.21% pirimiphos-methyl (75% - 97%), and high resistance to 0.03% deltamethrin (20-70%). PBO pre-exposure partially restored pyrethroid susceptibility. Genotyping detected high frequency of 1534C allele (0.92) and moderate 1016I (0.1-0.32). The V410L mutation was detected in Burkina Faso for the first time (frequency 0.1-0.36). Mosquitoes surviving 4 h exposure to 0.03% deltamethrin had significantly higher frequencies of the F1534C mutation than dead mosquitoes (0.70 vs. 0.96, p 0.0001) and mosquitoes surviving 2 - 4 h exposure had a significantly reduced life span. Ae. aegypti from Burkina Faso are resistant to multiple insecticide classes with multiple mechanisms involved, demonstrating the essential role of insecticide resistance monitoring within national dengue control programmes.

Background: Malaria remains a major public health threat in Burkina Faso. In most sub-Saharan African countries, malaria control relies mainly on long-lasting insecticide-treated nets (LLINs) and indoor residual spray (IRS). In Burkina Faso, long-term selection pressure exerted on malaria vectors by insecticide used in agriculture, has been exacerbated by countrywide LLINs distribution campaigns conducted every three years since 2010. The current study investigated insecticide resistance and the mechanisms involved in the malaria vector populations of the Anopheles gambiae complex in urban localities of Ouagadougou, Burkina Faso. Methods: Anopheles gambiae s. l. larvae were collected from three localities of Ouagadougou from July to September 2018, and reared in the laboratory to adults. The susceptibility profile to pyrethroid, carbamate, and organophosphate insecticides was assessed using World Health Organization (WHO) tube assays. PCR was used for mosquito species identification and to detect insecticide target-site mutations involved in insecticide resistance. Results: More than 95% of the collected An. gambiae s. l. were identified as An. arabiensis. WHO susceptibility assays revealed that, in all localities, An. arabiensis displayed high resistance to permethrin and deltamethrin (mortalities both kdr mutations 1014F (0.81) and 1014S (0.18) were recorded, although carbamate and organophosphate-associated Ace-1 119S mutation was not found. Conclusion: High pyrethroid resistance, underpinned, at least in part by high-frequency knockdown resistance mutations, in the urban malaria vector population suggests the potentially poor performance of pyrethroid-only LLINs in the cities where they are distributed. This result supported the switch to next generation LLINs, which are not solely reliant on pyrethroids to kill host-seeking mosquitoes in the cities of Burkina Faso.