Analyse de la résistance aux insecticides des populations d’Aedes aegypti et d’Aedes albopictus (Diptera : Culicidae), vecteurs d’arboviroses au Cameroun.

Abstract

Arboviruses such as dengue, chikungunya and Zika viruses are increasingly reported in Cameroon. These viruses are transmitted to humans by the bite of infected mosquitoes of Aedes genus mainly Aedes aegypti Linné, 1762 and Aedes albopictus Skuse, 1894. As there is no specific treatment or effective vaccine against these arboviruses, vector control remains the cornerstone to prevent the transmission of these viruses and for dealing with epidemics. In Cameroon, data on the insecticide resistances of Aedes vectors and underlying mechanisms needed for outbreak preparedness remain scarce. This study therefore aims to analyse the nationwide resistance profile of A. aegypti and A. albopictus to insecticides and to explore the potential resistance mechanisms involved. For this purpose, immature stages of Aedes were collected between March and July 2017 in 24 locations across Cameroon, transported to the insectary and reared until G1/G2 and G3 generation. Larval and adult bioassays were carried out according to WHO recommendations. F1534C mutation was genotyped using allele specific PCR in field collected adults (Go) and the polymorphism of the sodium channel gene was also assessed. In the aim to assess the involvement of metabolic resistance, [piperonylbutoxide (PBO) and diethyl maleate (DEM)] assays were carried out in one hand and in other hand real time PCR were used to evaluate the expression of some gens known as involved in the insecticide resistance. Larval bioassays with temephos and / or Bti showed the susceptibility for both Aedes species tested. Adult bioassays showed a variable level of resistance according to the species, the insecticide used and the sampling location. Thus, while a high level of susceptibility to pyrethroids was observed in most A. aegypti samples, those of A. albopictus rather presented very high levels of resistance, especially to permethrin (34.16% - 85.23% of mortality rate). Both species were resistant to DDT (12.42% - 87.1%), propoxur (60.8% - 88.9%) but totally susceptible to fenitrothion. A full or partial recovery of susceptibility was observed when mosquitoes were pre-exposed to PBO or DEM and then to DDT and permethrin. The CYP6P12 gene was found to be significantly overexpressed in samples of A. albopictus from Bafang and Bertoua compared to the susceptible strain VCRU. Genotyping and sequencing of a portion of the sodium channel detected the F1534C mutation in two samples of A. aegypti resistant to pyrethroids, with an allelic frequency of 3.3% (Edéa) and 33.3% (Douala). However, the low genetic diversity in the voltage gate sodium channel gene suggests a recent introduction of this mutation in Cameroon.The data generated by this study show that vector control actions should take into account the specificity of each locality and a regular and continuous resistance monitoring would be necessary to select the most effective insecticides for Aedes control.