article · Journal of Medical Entomology
Mosquitoes of the species Anopheles funestus contribute to malaria transmission in Côte d'Ivoire, but their insecticide susceptibility patterns have been poorly documented. Research in Toumbokro assessed resistance in Anopheles funestus s.s. against common insecticides and examined underlying metabolic mechanisms. Laboratory tests revealed that the mosquitoes were resistant to permethrin, deltamethrin, lambda-cyhalothrin, and DDT, with mortality rates ranging between 44% and 78%. Pre-exposure to the synergist piperonyl butoxide completely restored susceptibility to the tested pyrethroids, achieving 100% mortality, while partially restoring susceptibility to DDT. Furthermore, biochemical analyses identified significantly higher activity of cytochrome P450 monooxygenase enzymes compared to a susceptible control strain. These findings show that metabolic mechanisms drive resistance to pyrethroids and DDT in this local vector population, suggesting that malaria control strategies should deploy piperonyl butoxide-based or dual-active ingredient insecticidal nets.
Standard long-lasting insecticidal nets rely heavily on pyrethroids to protect communities against malaria. When malaria vectors develop metabolic resistance, these primary interventions become less effective, allowing transmission to persist. Identifying specific resistance pathways helps public health planners deploy effective alternatives, such as bed nets incorporating piperonyl butoxide or multiple active ingredients, to maintain insect control in affected regions.
This research directly informs public health buyers, vector control programmes, and bed net manufacturers. By demonstrating that enzyme inhibitors overcome resistance, the findings support the procurement and targeted deployment of piperonyl butoxide-based or dual-active ingredient insecticidal nets over standard pyrethroid nets. As these formulations already exist, the findings represent applied and tested field data that can immediately direct regional intervention choices.
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Insecticide resistance in malaria vectors threatens control efforts. Anopheles funestus Giles s.l. increasingly contributes to malaria transmission in Côte d'Ivoire especially in central and western regions, yet resistance data remain poorly known. This study assessed the susceptibility of An. funestus s.s. from Toumbokro to major insecticides and identified underlying metabolic resistance mechanisms. Blood-fed An. funestus s.l. females were collected indoors with an electric aspirator and induced to oviposit. F1 progeny from PCR-confirmed An. funestus s.s. were exposed to permethrin (0.75%), deltamethrin (0.05%), lambda-cyhalothrin (0.05%), and DDT (4%) in WHO tube assays. Synergist assays with piperonyl butoxide (PBO) were used to evaluate enzyme-mediated resistance, and biochemical assays were used to measure activity of detoxification enzymes. Anopheles funestus s.s. showed resistance to all insecticides, with mortality rates of 78% (permethrin), 76% (deltamethrin), 44% (lambda-cyhalothrin), and 72% (DDT). Pre-exposure to PBO fully restored susceptibility to pyrethroids (100% mortality), implicating metabolic resistance, but only partially restored susceptibility to DDT (82%). Biochemical assays confirmed significantly greater cytochrome P450 monooxygenase activity in An. funestus s.s. (0.00144 nmol/mg of protein) compared with the susceptible Kisumu strain (0.00085 nmol/mg of protein). An. funestus s.s. from Toumbokro in central Côte d'Ivoire is resistant to pyrethroids and DDT, mainly via metabolic mechanisms. This resistance likely sustains its role in malaria transmission despite widespread pyrethroid-treated long-lasting insecticidal nets (LLIN) use suggesting a need for PBO-based or dual-active ingredient LLINs in vector control strategies.
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DOI: 10.1093/jme/tjag137
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