It was the outcome of his defense held on December 12th 2024, at the Faculty of Science of the University of Yaoundé I.
Bertrand Mbakam with members of the jury
His study was titled “Role of the new V402L and I1527T mutations of the Voltage Gated Sodium Channel (VGSC) gene in pyrethroid resistance in Anopheles coluzzii in Cameroon”. To carry out this study, he was guided by the observation that the growing resistance to pyrethroids, the leading insecticides against malaria vectors, poses a significant threat to public health. From his observation, the L995F and L995S mutations in the VGSC gene are well established as being linked to this resistance and are frequently detected in resistance management programmes. Recently, new mutations, V402L and I1527T were identified and found associated with resistance in other mosquito species.
What do V402L and I1527T stand for?
V402L is a code which indicates that there are two distinct mutations on a protein sequence of the VGSC gene at positions 402 and 1527: V402L means that the amino acid, Valine (V) at position 402 on the gene has been replaced by Leucine (L). I1527T means that the amino acid, Isoleucine (I) at position 1527 on the gene has been replaced by Threonine (T).
Bertrand Mbakam’s study explores the role of these mutations in pyrethroid resistance in Anopheles coluzzii in Cameroon. Pyrethroids are synthetic insecticides, which are mainly used for the controlling insect pests in agriculture, public health, and animal health. After collecting samples from the CRID bio-bank, molecular identification was confirmed by Polymerase Chain Reaction (PCR) – a technique for targeted DNA replication in vitro, which makes it possible to obtain large quantities of a specific DNA fragment of defined length from a complex, sparse sample (SINE 200 PCR). The latter is a PCR technique used to identify the different species of the Anopheles gambiae mosquito complex.
Mbakam’s results make Cameroon eligible to apply for the supply of new technology mosquito nets.
A real-time polymerase chain reaction (qPCR) method using locked nucleic acids (LNA) was developed to genotype the VGSC V402L and I1527T mutations, in order to assess their spatiotemporal distribution and their association in pyrethroid resistance in Anopheles coluzzii. LNA improves polymerase chain reaction and enables highly sensitive and specific analysis of short RNA and DNA targets. Anopheles coluzzii was found to be the dominant species in the localities studied, with mutant alleles 402L(T) and 1527T present in 2022 at variable frequencies.
These mutations predominate in the Far North and North of Cameroon, while their frequency is significantly lower in the littoral, the Centre and in the South regions. Spatio-temporal analysis indicates that these mutant alleles became dominant in 2022, with their presence noted since 2018-2019. Mosquitoes exposed to pyrethroids show significant variations according to genetic markers. The RS genotype was observed only in the alive exposed to permethrin 1X at 18%, representing 9% of the R allele, which is dominant in the exposed alive. Statistical analysis revealed that the RS genotype conferred better survival to permethrin 1X with a significant p-value (<0.0001), while the presence of the R allele also conferred significant resistance to this dose (p=0.0032). The RR homozygous genotype showed superior survival to permethrin 5X, with a significant p-value indicating that it could allow survival at this higher dose (p=0.0414). For VGSC I1527T, the heterozygous RS genotype showed superior survival to deltamethrin 1X, with a significant p-value indicating that it could allow survival to this insecticide (RS vs SS: p=0.0273). The RR and RS genotypes were only present in live animals exposed to permethrin 1X (12% and 6%), showing significant survival compared with the SS genotype (RR vs SS: p=0.0001 and RS vs SS: p=0.0096) and the R allele conferred significant resistance compared with S (p<0.0001). For permethrin 5X, the RS and RR genotypes showed significant p-values indicating that they could survive this higher exposure compared to the SS genotype (p=0.0029 for RS vs SS; p=0.0002 for RR vs RS).
In conclusion, substitutions V402L(T) and I1527T confer resistance to pyrethroids in A. coluzzii in Cameroon. This result makes Cameroon eligible to apply for the supply of new technology mosquito nets. At the end of his defense, Bertrand Mbakam was awarded a grade of 94/100 by the jury chaired by Prof Penlap Véronique from the University of Yaoundé I.
