This study is an assessement of the susceptibility profile of Anopheles gambiae sensu lato with respect to carbamates and organophosphate and the distribution of the molecular mechanism underlying resistance to these insecticides.
Malaria remains a major public health in Cameroon
“Distribution of acetylcholinesterase (Ace‑1R) target-site G119S mutation and resistance to carbamates and organophosphates in Anopheles gambiae sensu lato populations from Cameroon” is the recent study published by Achille Binyang and collaborators. Because malaria remains a major public health in Cameroon, the Government is considering the implementation of indoor residual spraying (IRS) as complementary measure to control malaria in the context of high pyrethroid resistance in major malaria vectors. The researcher argue that non-pyrethroid insecticide classes such as organophosphates and carbamates may be utilized in IRS but, the success of this strategy depends on good knowledge of the susceptibility status of malaria vectors to these insecticides.
Significant results
A total of 2188 adult female mosquitoes from the nine study sites across the country were exposed to two carbamates (bendiocarb and propoxur); and one organophosphates (pirimiphos-methyl). Analyses revealed that Anopheles gambiae population from Cameroon present a variable resistance to bendiocard and propoxur but exhibit a susceptibility to pirimiphos-methyl. Three mosquito species were identified among the Anopheles gambiae complex : Anopheles coluzzii, Anopheles gambiae and Anopheles arabiensis. They distribution was varieted. Anopheles gambiae was found in southern part of the country while Anopheles arabiensis was found in the northern part. Anopheles coluzzii was found in both part. Genotyping of Ace 1R mutation conferring resistance to carbamates and organophosphates insecticides show that mosquitoes carrying the resistance allele were significantly more likely to survive after exposure to bendiocarb than those with the susceptibility allele. Homozygote-resistant mosquitoes displayed a higher ability to survive than homozygote-susceptible mosquitoes. Also, heterozygote-resistant mosquitoes were significantly more likely to survive than homozygote-susceptible mosquitoes. The distribution of this mutation overlapped with that of Anopheles gambiae and was found only in the southern part of the country.
This study showed that Anopheles gambiae s.l. populations from Cameroon were fully susceptible to organophosphates but exhibited variable susceptibility to carbamates across the country. These carbamate resistance was associated with the presence of the Ace-1 G119S mutation, which was detected only in Anopheles gambiae species. Overall, the organophosphate insecticide class would be more suitable than carbamates for IRS in Cameroon, especially in the southern part of the country. However, because the potential spread of the Ace-1 G119S mutation could compromise the efficacy of such a strategy, periodic updates of its distribution and data on resistance of Anopheles gambiae s.l. mosquitoes should be performed to guide the implementation of IRS strategies in Cameroon.
Binyang AJ, Elanga-Ndille E, Tene-Fossog B, Ndo C, Nouage L, Assatse T, Fotso-Toguem Y, Tabue R, Zeukeng F, Nguiffo DN, Etang J, Njiokou F, Wondji CS Distribution of acetylcholinesterase (Ace-1R) target-site G119S mutation and resistance to carbamates and organophosphates in Anopheles gambiae sensu lato populations from Cameroon.Parasit Vectors. 2022 Feb 14;15(1):53. doi: 10.1186/s13071-022-05174-1.PMID: 35164852
