(A) Geographical representation of collection sites in Cameroon. The study sites are represented by stars. The color represents the targeted species. (B) Susceptibility profile using WHO bioassay tube test according to the study sites. Mortality rates were recorded 24 h post-exposure to the discriminating concentration of insecticides. Data are shown as mean ± standard error. Mosquitoes were sampled both pirimiphos-methyl and malathion tests on the same day at Gounougou (December 2021) and Mibellon (October 2021)
Mosquitoes are becoming increasingly resistant to insecticides. As older insecticides such as pyrethroids become less effective, a different class of insecticides—organophosphates like pirimiphos-methyl (PM)—has been proposed as a possible alternative.
This study investigated how mosquitoes in six regions of Cameroon respond to two organophosphates: PM and malathion. It focused on three major mosquito species: Anopheles gambiae, Anopheles coluzzii, and Anopheles funestus. While most Anopheles coluzzii and Anopheles funestus mosquitoes were still susceptible, populations of Anopheles gambiae—especially in farming areas—showed resistance.
This resistance is linked to a genetic mutation called Ace-1R. Furthermore, the study found that many resistant mosquitoes carry multiple copies of this mutation—a phenomenon known as copy number variation (CNV). This genetic trait gives mosquitoes a better chance of surviving insecticide exposure.
Although Cameroon has not yet implemented Indoor Residual Spraying (IRS), this research highlights the urgent need to monitor not only resistance levels, but also the genetic changes behind them. These findings help lay the groundwork for smarter, evidence-based malaria control strategies that could save lives across the country.
This study was led by Dr Judith Dandi, Post-doctoral researcher at CRID. Read more: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0321825
