Insecticide susceptibility of Aedes aegypti and Aedes albopictus in Central Africa

Abstract

Background: Aedes aegypti(Linnaeus, 1762) andAedes albopictus(Skuse, 1894) are the main vectors of dengue (DENV) and chikungunya (CHIKV) viruses worldwide. As there is still no vaccine or specific treatment for DENV and CHIKV, vector control remains the cornerstone of prevention and outbreak control. Unfortunately, vector control programs are facing operational challenges with mosquitoes becoming resistant to commonly used insecticides in several areas through the world. Throughout Central Africa no recent data are available susceptible/resistant status of either vector species since the introduction/arrival ofAe. albopictusin this area. We therefore studied the level of resistance of these two major vectors to insecticides commonly used in Africa for mosquito control.Results: Aedes aegyptiandAe. albopictuswere sampled in six urban localities of Cameroon (Garoua, Bertoua, Yaoundé, Bafia, Buea) and Gabon (Libreville). Larval bioassays, carried out to determine the lethal concentrations (LC₅₀and LC₉₅) and resistance ratios (RR₅₀and RR₉₅) suggested that both vector species were susceptible toBti(Bacillus thuringiensis var israeliensis) and temephos. Bioassays were also performed on adults using WHO diagnostic test kits to assess phenotypic resistance to deltamethrin, DDT, fenitrothion and propoxur. These experiments showed that one population ofAe. aegypti(Libreville) and two populations ofAe. albopictus(Buea and Yaoundé) were resistant to DDT (mortality 36% to 71%). Resistance to deltamethrin was also suspected inAe. albopictusfrom Yaoundé (83% mortality). All other field mosquito populations were susceptible to deltamethrin, DDT, fenitrothion and propoxur. No increase in the knockdown times (Kdt₅₀and Kdt₉₅) was noted in the Yaoundé resistant population compared to otherAe. albopictuspopulations, suggesting the possible involvement of metabolic resistance to deltamethrin and DDT.Conclusion: In view of the recent increase in dengue and chikungunya outbreaks in Central Africa, these unique comparative data on the insecticide susceptibility ofAe. aegyptiandAe. albopictuscould help public health services to design more effective vector control measures.