Distribution of Anopheles gambiae s.l siblings, insecticide resistance and prevalence of markers of resistance (Kdr & Ace-1) in Edea and Buea: forest region of Cameroon

Background:

The complexity and heterogeneity of malaria transmission in Cameroon is enhanced by the different eco-systems and topology which enhance the proliferation of Anopheline mosquitoes. Though long-lasting insecticide-treated nets have been massively distributed across the country, malaria still remains a significant public health concern, with innate and adaptive resistance mechanisms exploited by malaria vectors against different insecticides; the micro-ecological variations in Cameroon could be playing a viral role in the expression of essential insecticide resistance genes in malaria vectors. Thus, this study sought to assess and compare phenotypic resistance to commonly used insecticides and the prevalence of markers of insecticide resistance to Anopheles gambiae s.l from two localities within the forest ecological zone of Cameroon.

Material and methods:

Three to five days mosquitoes obtained from larva collected at eight breeding sites in Buea and Edea were morphologically identified and phenotypic resistance to pyrethroid, organophosphate and carbamate insecticides assessed using the WHO bioassay protocol. Molecular speciation of An. gambiae s.l and the prevalence of L1014F and Ace-1R G119S mutations was assessed using PCR. Results:

Anopheles coluzzii and An. gambiae were the only siblings species identified in both communities, with An. coluzzii being the dominant sibling in Edea and the latter in Buea. Anopheles gambiae s.l was resistance to diagnostic concentrations of all insecticides in Buea but susceptible to 1X bendiocarb and 1X pirimiphosmethyl in Edea. In both communities, mortality increased with increasing concentration of alphacypermethrin, permethrin, pirimiphosmethyl and bendiocarb while PBO had a synergistic effect on all pyrethroid insecticides tested. There was a significant difference in the mortality to 1X permethrin (p = 0.014),1X permethrin + PBO (p = 0.001), 5X permethrin (p < 0.001), 1X alphacypermethrin + PBO (p < 0.001), 1X pirimiphosmethyl (p < 0.001) and 1X bendiocarb (p < 0.001) in Buea compared to Edea.

Conclusion: Anopheles gambiae and An. coluzzii were the major malaria vectors in both communities.Though these vectors were resistant to the diagnostic dose of all insecticides in Buea, they were susceptible to 1X bendiocarb and 1X pirimiphosmethyl in Edea.