On February 20, 2026, Tagne Djoko Simeon Carlos successfully defended his Ph.D. thesis in the Department of Biochemistry at the Faculty of Science of the University of Bamenda.
Carlos Djoko and his supervisors
His research, titled “Genetic Diversity, Functional Validation and Cis-Regulatory Elements of Cytochrome P450 CYP9K1 in Resistance to Pyrethroid Insecticide in the Malaria Vector Anopheles funestus,” received high praise from an international jury of experts, who awarded him the distinction of “Excellent” in recognition of the quality and significance of his work. The thesis was co-supervised by Prof. Mbouobda Hermann Désiré from the University of Bamenda and Prof. Charles Wondji from the Liverpool School of Tropical Medicine (LSTM), United Kingdom.
Research Conducted
Dr. Djoko carried out his doctoral research at CRID, where he employed advanced functional genetics and genomics approaches to investigate insecticide resistance in Anopheles funestus, one of the major malaria vectors in Africa. His work focused on the detailed characterization of the candidate gene CYP9K1, leading to the identification of important genetic variations responsible for pyrethroid resistance in mosquito populations. Beyond advancing scientific understanding, the study also contributed to the development of molecular diagnostic tools that are now being integrated into vector control strategies to monitor the spread of metabolic resistance in wild mosquito populations.
One of the major findings of the study was the discovery of the rapid expansion of the G454A-CYP9K1 haplotype, a resistant genetic variant initially identified only in East Africa. Through temporal analyses of genetic diversity and allele frequency changes, the research demonstrated strong positive selection of the 454A mutant allele across East Africa and parts of Central Africa.
While the mutation was first detected at high frequencies in Anopheles funestus populations from East Africa in 2014, it was absent in other African regions at that time. Remarkably, by 2020, the same Ugandan haplotype had been identified at very high frequency in Cameroon, highlighting the rapid and complex geographical spread of insecticide resistance across distant regions of the continent.
Understanding How the Mutation Confers Resistance
Dr. Djoko’s research also demonstrated the direct functional role of the G454A mutation in increasing mosquito resistance to pyrethroid insecticides. Comparative in vitro metabolism assays revealed that the mutant-type 454A-CYP9K1 (R) allele metabolizes pyrethroids more efficiently than the wild-type G454-CYP9K1 (S) allele.
Further experiments using transgenic Drosophila melanogaster flies expressing the resistant allele confirmed significantly higher resistance to both type I and type II pyrethroids. In addition, laboratory bioassays and field experimental hut trials conducted in Cameroon showed that mosquitoes carrying the homozygous resistant genotype 454A/A-CYP9K1 (RR) survived exposure to pyrethroid insecticides more successfully. These findings illustrate how single nucleotide mutations can enhance detoxification enzyme activity, allowing mosquitoes to break down insecticides before they reach their biological target. This mechanism contributes directly to the reduced effectiveness of insecticide-treated bed nets widely used in malaria control programs.
Carlos Djoko’s studies resulted in the publication of two scientific articles:
Development of Novel Diagnostic Tools
Another significant contribution of this work was the development of innovative DNA-based molecular diagnostic tools capable of detecting and monitoring CYP9K1-mediated metabolic resistance in field mosquito populations.
Dr. Djoko developed both allele-specific PCR (AS-PCR) and locked nucleic acid PCR (LNA-PCR) assays, enabling rapid and cost-effective identification of resistance-associated mutations. These tools provide valuable support for tracking the efficacy of malaria interventions and assessing potential cross-resistance with newly introduced insecticides before deployment in the field.
By equipping National Malaria Control Programs (NMCPs) with predictive resistance-monitoring tools, this research offers practical solutions for improving resistance management strategies and strengthening malaria control efforts across endemic regions.
