Abstract
A key factor affecting malaria vector control efforts in Cameroon is the rapid expansion of insecticide resistance in Anopheles gambiae s.l (An. gambiae) populations; however, mechanisms involved in insecticide resistance in forest mosquito populations are still not well documented yet. The present study was conducted to screen molecular mechanisms conferring insecticide resistance in An. gambiae s.l. populations from the South Cameroon forest region. WHO bioassays were conducted with F0 An. gambiae females aged three to four days from forest (Sangmelima, Nyabessan, and Mbandjock) and urban sites (Yaoundé (Bastos and Nkolondom)), against pyrethroids (permethrin 0.75% and deltamethrin 0.05%) and carbamates (bendiocarb 0.1%). Members of the An. Gambiae s.l. species complex were identified using molecular diagnostic tools. TaqMan assays were used to screen for target site mutations. The expression profiles of eight genes implicated in insecticide resistance were assessed using RT-qPCR. Cuticle hydrocarbon lipids were measured to assess their potential implication in insecticide resistance. Both An. Gambiae and An. coluzzii were detected. An. gambiae was highly prevalent in Sangmelima, Nyabessan, Mbandjock, and Nkolondom. An. coluzzii was the only species found in the Yaoundé city center (Bastos). Low mortality rate to both pyrethroids and bendiocarb was recorded in all sites. High frequency of L1014F allele (75.32–95.82%) and low frequencies of L1014S (1.71–23.05%) and N1575Y (5.28–12.87%) were recorded. The G119S mutation (14.22–35.5%) was detected for the first time in An. gambiae populations from Cameroon. This mutation was rather absent from An. coluzzii populations. The detoxification genes Cyp6m2, Cyp9k1, Cyp6p4, Cyp6z1, as well as Cyp4g16 which catalyzes epicuticular hydrocarbon biosynthesis, were found to be overexpressed in at least one population. The total cuticular hydrocarvbon content, a proxy of cuticular resistance, did not show a pattern associated with pyrethroid resistance in these populations. The rapid emergence of multiple resistance mechanisms in An. Gambiae s.l. population from the South Cameroon forest region is of big concern and could deeply affect the sustainability of insecticide-based interventions strategies in this region.
Highlights
According to the 2018 World malaria report, Cameroon is classified as one of 11 countries most affected by malaria in the world [1]
The present study focuses on the analysis of the insecticide resistance status, underlying molecular mechanisms conferring resistance in forest and city An. gambiae populations from Cameroon
Mortality rate varied between 4–12% for deltamethrin 0.05% and 3–12% for permethrin
Summary
According to the 2018 World malaria report, Cameroon is classified as one of 11 countries most affected by malaria in the world [1]. The whole country is exposed to malaria transmission risk with high and perennial transmission occurring in the forest region [2,3]. The rapid deforestation taking place in the forest region has provided suitable breeding opportunities for An. gambiae, which in most forest settings is becoming the predominating species responsible for most malaria transmission cases [6,7,8,9]. In Cameroon, members of the An. gambiae complex consist of An. gambiae, An. coluzzii, An. melas, and An. arabiensis, but only An. gambiae and An. coluzzii have been reported from forest settings [4,5]. Local forest anopheline species are still highly susceptible to insecticides due to their high exophilic and exophagic behavior [10], studies conducted so far suggested increased insecticide resistance in An. gambiae s.l. populations [8,11]. There is still not enough information on mechanisms conferring resistance to these forest An. gambiae s.l. populations
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