Status of pfcrt and pfmdr1 mutations in Plasmodium falciparum isolates in Gabon in 2019 after chloroquine withdrawal.

Chloroquine (CQ) resistance has long contributed to antimalarial treatment failure. Despite the implementation of artemisinin-based combination therapies (ACTs) in Gabon, continued surveillance of antimalarial drug resistance markers remains essential for malaria control and elimination. This study aimed to monitor molecular markers of antimalarial drug resistance, specifically the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multidrug resistance 1 (pfmdr1), in P. falciparum clinical isolates from Libreville, nearly two decades after CQ withdrawal. Archived dried blood spots collected in 2019 were retrieved to assess the prevalence of pfcrt and pfmdr1 mutations and haplotypes in P. falciparum isolates. In total, 70 samples were successfully genotyped via Sanger sequencing. Single nucleotide polymorphisms (SNPs) associated with antimalaria drug resistance were identified in 25.71% of pfcrt and 20% of pfmdr1. For pfcrt, the most frequent mutation was N75(E/K) (24.3%), followed by M74I (22.86%) and K76T (17.14%). Moreover, malaria-positive individuals exhibited mainly the wild-type haplotype CVMNK (74.29%), while the mutant haplotype CVIET (17.13%) was the most common among the mutant variants. The frequency of CVIET observed in this study is substantially lower than the previously reported frequency in Gabon. Other mutant haplotypes, including CVINK, CVMEK, CVMNT, CVIEK, and CVIKK, were each detected at low frequencies (1.43%). Similarly, for pfmdr1, the most frequent mutation was Y184F (18.57%), which predominantly produced the mutant haplotype NEFND (15.71%), compared with YEFND (2.86%) and NEYDD (1.43%). Nevertheless, the wild-type haplotype NEYND was observed in 80% of the study population. These finding indicate the persistence of mutant genotypes in both pfcrt and pfmdr1, along with a decline in their frequencies over time, suggesting a progressive restoration of CQ susceptibility. The results underscore the importance of longitudinal CQ resistance monitoring to accurately assess its prevalence and inform public health interventions.