Multiple insecticide resistance and Plasmodium infection in the principal malaria vectors Anopheles funestus and Anopheles gambiae in a forested locality close to the Yaoundé airport, Cameroon

Abstract

<ns4:p><ns4:bold>Background:</ns4:bold>Reducing the burden of malaria requires better understanding of vector populations, particularly in forested regions where the incidence remains elevated. Here, we characterized malaria vectors in a locality near the Yaoundé international airport, Cameroon, including species composition, abundance,<ns4:italic>Plasmodium</ns4:italic>infection rate, insecticide resistance profiles and underlying resistance mechanisms.</ns4:p><ns4:p><ns4:bold>Methods:</ns4:bold>Blood-fed adult mosquitoes resting indoors were aspirated from houses in April 2019 at Elende, a locality situated 2 km from the Yaoundé-Nsimalen airport. Female mosquitoes were forced to lay eggs to generate F<ns4:sub>1</ns4:sub>adults. Bioassays were performed to assess resistance profile to the four insecticides classes. The threshold of insecticide susceptibility was defined above 98% mortality rate and mortality rates below 90% were indicative of confirmed insecticide resistance. Furthermore, the molecular basis of resistance and<ns4:italic>Plasmodium</ns4:italic>infection rates were investigated.</ns4:p><ns4:p><ns4:bold>Results:</ns4:bold><ns4:italic>Anopheles funestus</ns4:italic>s.s. was the most abundant species in Elende (85%) followed by<ns4:italic>Anopheles gambiae</ns4:italic>s.s. (15%) with both having similar sporozoite rate. Both species exhibited high levels of resistance to the pyrethroids, permethrin and deltamethrin (&lt;40% mortality).<ns4:italic>An. gambiae</ns4:italic>s.s. was resistant to DDT (9.9% mortality) and bendiocarb (54% mortality) while susceptible to organophosphate.<ns4:italic>An. funestus</ns4:italic>s.s. was resistant to dieldrin (1% mortality), DDT (86% mortality) but susceptible to carbamates and organophosphates. The L119F-GSTe2 resistance allele (8%) and G119S<ns4:italic>ace</ns4:italic>-1 resistance allele (15%) were detected in<ns4:italic>An. funestus</ns4:italic>s.s. and<ns4:italic>An. gambiae</ns4:italic>s.s., respectively<ns4:italic>.</ns4:italic>Furthermore, the high pyrethroid/DDT resistances in<ns4:italic>An. gambiae</ns4:italic>corresponded with an increase frequency of 1014F<ns4:italic>kdr</ns4:italic>allele (95%). Transcriptional profiling of candidate cytochrome P450 genes reveals the over-expression of<ns4:italic>CYP6P5</ns4:italic>,<ns4:italic>CYP6P9a</ns4:italic>and<ns4:italic>CYP6P9b.</ns4:italic></ns4:p><ns4:p><ns4:bold>Conclusion:</ns4:bold>The resistance to multiple insecticide classes observed in these vector populations alongside the significant<ns4:italic>Plasmodium</ns4:italic>sporozoite rate highlights the challenges that vector control programs encounter in sustaining the regular benefits of contemporary insecticide-based control interventions in forested areas.</ns4:p>