Chloroquine resistance transporter drives divergent multi-locus drug resistance genetic backgrounds and susceptibility in Gambian Plasmodium falciparum.

OBJECTIVE

Sustained antimalarial drug use against Plasmodium falciparum has often resulted in drug resistance and the selection of associated genetic markers in malaria endemic populations. The genetic markers of resistance to legacy drugs like chloroquine persist in The Gambia. This study assesses the effect of these legacy drug-resistance genomic backgrounds on in vitro responses to antimalarial drugs in The Gambia.

METHODS

P. falciparum drug-resistance genotypes at pfcrt, pfmdr1, pfdhfr, pfdhps, and pfkelch13 genes was determined from amplicon sequencing of 364 isolates. In vitro 50% growth inhibitory concentrations (IC50s) were determined for 68 isolates to chloroquine, dihydroartemisinin, lumefantrine, mefloquine, piperaquine, and amodiaquine. In vitro response to drugs was assessed for parasite groups with different major multi-locus drug-resistance genetic backgrounds.

RESULTS

Two main multi-locus drug-resistance backgrounds driven by pfcrt haplotypes (CVMNK/CVIET) were observed. CVIET (62%) isolates were resistant to chloroquine, whereas CVMNK was less sensitive to mefloquine and dihydroartemisinin. The pfmdr1 NFD haplotype was 60% prevalent, with 184F at 67%. Infections with the CVIET-NFD combination (31.7%) had the highest chloroquine IC₅₀s. Pfdhfr S108N (98%) and pfdhps A437G (85%) mutants were highly prevalent. No validated pfkelch13 resistance mutations were detected.

CONCLUSIONS

Artemisinin-based combination therapies remain effective in The Gambia, supported by the absence of pfkelch13 mutations. However, reversion to chloroquine sensitivity tends to result in reduced sensitivity to artemisinin-based combination therapy drugs. These genotype-phenotype dynamics need continuous monitoring to guide drug interventions towards malaria elimination.