This study by Tekoh Theofelix Anyerengu, aimed at characterizing the resistance profiles and elucidating the underlying molecular bases for Carbamate resistance in Fumoz Anopheles funestus laboratory population.
The specific objectives of this study were firstly, to assess the level of susceptibility of crosses of Anopheles funestus lab colonies (Fumoz and Fang) to carbamates; secondly, to assess the correlation between CYP6P9a and the 6.5 kb insertion resistance markers in Anopheles funestus and the ability to survive exposure to carbamates; thirdly, to confirm the role of the over expression of CYP6P9a on carbamate resistance by assessing the susceptibility of transgenic Drosophila melanogaster flies over expressing the gene. The long-term objective of this research is to provide a DNA-based assay to track and monitor any emergence and/or surge of carbamate resistance by Anopheles funestus. This will contribute to the development of suitable resistance management tools against malaria. This research elucidated the role of the P450s; CYP6P9a gene and the 6.5 kb structural variation (SV) in carbamate resistance. This was achieved by correlating the insecticide resistance phenotype with the CYP6P9a and the 6.5 kb SV genotypes. The exposure of transgenic flies overexpressing only CYP6P9a to carbamates, was to establish that, the overexpression of this gene can independently confer carbamate resistance. From this study, it was concluded that, Anopheles funestus mosquito hybrids established from crosses between the resistant (Fumoz) and susceptible strain (Fang) which expressed CYP6P9a were resistant to carbamate insecticides (0.1% propoxur and 0.1% bendiocarb). A strong association was found between the CYP6P9a gene and the 6.5 kb structural variation, and the ability of Anopheles funestus to survive exposure to carbamates especially the homozygous genotype. QRT-PCR results of alive hybrid mosquitoes after exposure to carbamate insecticides showed that, the gene is not induced and normal expression of this gene can confer carbamate resistance in mosquitoes. This study confirmed that this gene can be used as a diagnostic tool to track the resistance of Anopheles funestus to carbamates.
Many factors had influenced and determined the choice of this research carried out by Tekoh Theofelix Anyerengu. In 2017, the National Malaria Control Program (NMCP) revealed that in Cameroon, malaria is responsible for about 13% of the total annual deaths, 58% of occurrences and around 30% of the population had at least one episode of malaria each year. Vector control strategies based on the use of insecticides targets female Anopheles mosquitoes. These control strategies have proven to be the most effective way of fighting malaria with an estimated 663 million cases averted between 2000 and 2015. NMCP recognizes that, in 2016, malaria control in Cameroon has witnessed a significant scale-up of vector control intervention (70.9%) through the distribution of Long-Lasting Insecticidal Nets (LLINs). In the same periods, scientists claimed that the effectiveness of these insecticide-based control tools is threatened by the emergence of insecticide resistance in major malaria vectors across African countries, including Cameroon. The aim of this research was to elucidate the role of the CYP genes (CYP6P9a) and the 6.5 kb insertion in carbamate resistance in Anopheles funestus which have been found to be highly expressed in carbamate resistant mosquitoes from Mozambique.