Assessment of Genetic Polymorphisms Associated with Malaria Antifolate Resistance Among the Population of Libreville, Gabon

Background: Gabon is a malaria-threatened country with a stable and hyperendemic transmission of Plasmodium falciparum monoinfection. Malaria drug resistance is widely spread in many endemic countries around the world, including Gabon. The molecular surveillance of drug resistance to antifolates and artemisinin-based combination therapy (ACT) is one of the strategies for combating malaria. As Plasmodium parasites continue to develop resistance to currently available anti-malarial drugs, this study evaluated the frequency of the polymorphisms and genetic diversity associated with this phenomenon among the parasites isolates in Gabon.

Methods: To assess the spread of resistant haplotypes among the malaria-infected population of Libreville, single nucleotide polymorphisms linked to sulfadoxine-pyrimethamine (SP) and artemisinin drugs resistance were screened for P. falciparum dihydrofolate reductase (Pfdhfr), P. falciparum dihydropteroate synthase (Pfdhps), and P. falciparum kelch 13-propeller domain (Pfk13) point mutations.

Results: The analysis of 70 malaria-positive patient samples screened for polymorphism showed 92.65% (n = 63) mutants vs. 7.35% (n = 5) wild parasite population in Pfdhfr, with high prevalence mutations at SN(88.24%, n = 60), NI(85.29%, n = 58), CR(79.41%, n = 54); however, IL(2.94%, n = 2) showed low frequency mutation. No wild haplotype existed for Pfdhps, and there were no mutations at the KE, AG, and AT/S positions. However, the mutation rate at AG(93.38%, n = 62) was the highest, followed by SA/F(15.38%, n = 10). A higher frequency of quadruple IRNI-SGKAA (69.84%) than quintuple IRNI-(A/F)GKAA (7.94%) mutations was observed in the Pfdhfr-Pfdhps combination. Furthermore, none of the mutations associated with ACT resistance, especially those commonly found in Africa, were observed in Pfk13.

Conclusions: High polymorphism frequencies of Pfdhfr and Pfdhps genes were observed, with alternative alanine/phenylalanine mutation at SA/F (7.69%, n = 5) for the first time. Similar to that of other areas of the country, the patterns of multiple polymorphisms were consistent with selection owing to drug pressure. Although there was no evidence of a medication failure haplotype in the studied population, ACT drug efficacy should be regularly monitored in Libreville, Gabon.