Search

The paper describes the development of a long-lasting product for Intra-domicile residual spray (IRS) and shows it is possible to obtain a residual effect of nearly 2 years. However, to obtain that the methods currently recommended by WHO for laboratory evaluation had to be modified and approached methods closer to the semi-field and field evaluations as applied in later phases of WHO procedures. Surfaces with high pH resulted in short residual effect unless the formulations were mixed with a silicone coating. Screening in huts constructed for the purpose was realised by dividing the wall surfaces in 25 test plots of 0.5 m² where formulations were applied randomly with more repeats the closer to the final formulation. Mud and concrete surface were more challenging than wood surface and stones and these could be dropped for screening. Wall surfaces heated by sun were repellent to non-blood fed mosquitoes, and the test in huts were limited to the mornings. However, blood fed mosquitoes were not repelled. Cone tests on mud-walls are complicated by the uneven structure of the surface and a better way of attaching cones to avoid mortality errors was developed. Formulations that can be applied and last for two mosquito seasons produce big cost savings for IRS programs, since program costs are mostly application costs.

In West Africa, Aedes aegypti remains the major vector of dengue virus. Since 2013, dengue fever has been reemerging in Burkina Faso with annual outbreaks, thus becoming a major public health problem. Its control relies on vector control, which is unfortunately facing the problem of insecticide resistance. At the time of this study, although data on phenotypic resistance were available, information related to the metabolic resistance in Aedes populations from Burkina Faso remained very scarce. Here, we assessed the phenotypic and the metabolic resistance of Ae. aegypti populations sampled from the two main urban areas (Ouagadougou and Bobo-Dioulasso) of Burkina Faso. Insecticide susceptibility bioassays to chlorpyriphos-methyl 0.4%, bendiocarb 0.1% and deltamethrin 0.05% were performed on natural populations of Ae. aegypti using the WHO protocol. The activity of enzymes involved in the rapid detoxification of insecticides, especially non-specific esterases, oxidases (cytochrome P450) and glutathione-S-transferases, was measured on individual mosquitos. The mortality rates for deltamethrin 0.05% were low and ranged from 20.72% to 89.62% in the Bobo-Dioulasso and Ouagadougou sites, respectively. When bendiocarb 0.1% was tested, the mortality rates ranged from 7.73% to 71.23%. Interestingly, in the two urban areas, mosquitoes were found to be fully susceptible to chlorpyriphos-methyl 0.4%. Elevated activity of non-specific esterases and glutathione-S-transferases was reported, suggesting multiple resistance mechanisms involved in Ae. aegypti populations from Bobo-Dioulasso and Ouagadougou (including cytochrome P450). This update to the insecticide resistance status within Ae. aegypti populations in the two biggest cities is important to better plan dengue vectors control in the country and provides valuable information for improving vector control strategies in Burkina Faso, West Africa.