La résistance à la chloroquine de Plasmodium falciparum représente un problème majeur de santé publique particulièrement en Afrique sub-saharienne. Des mutations ponctuelles associées à la résistance à la chloroquine in vitro ont été trouvées dans les gènes pfmdr1 , pfcg2 et pfcrt codant pour des protéines transmembranaires. Des études de croisements génétiques et de transfections ont montré que pfmdr1 et pfcg2 n'étaient pas responsables de la chloroquino-résistance, mais pourraient avoir un rôle modulateur, alors que pfcrt semble être déterminant. Une étude in vivo conduite au Mali a montré la sélection de la mutation pfcrt K76T chez tous les sujets ayant présenté un échec thérapeutique à la chloroquine. Pourtant 37 % des sujets guéris avaient un Plasmodium également porteur de cette mutation. Afin de préciser l'association de pfcrt avec la chloroquino-résistance, la détermination du codon 76 de pfcrt ainsi que la chimiosensibilité in vitro ont été effectuées sur 146 isolats provenant de voyageurs le plus souvent non-immuns. Les résultats ont montré une forte association du génotype de pfcrt avec la chloroquino-résistance.

Recent transfection based studies demonstrated that cg2 , a candidate gene for chloroquine resistance in Plasmodium falciparum , was not the resistance determinant. A further analysis of the initial 36kb locus comprising the cg2 gene led to the discovery of another gene, pfcrt , which was absolutely associated with chloroquine resistance in forty parasite lines. The aim of this study was to evaluate, in 146 unselected clinical isolates obtained mostly from non-immune travellers returning from various endemic countries to France in years 1995-1999, the association between in vitro chloroquine resistance and the sequence of a part of the pfcrt gene. For comparison, the determination of the cg2 kappa and the pfmdr1 codon 86 genotypes were also performed on the same isolates. As determined by an isotopic semi-microtest, 70 isolates were susceptible to chloroquine (50% inhibitory concentration <80nM) and 76 were resistant. The amplification of a portion of the pfcrt gene spanning codons 72 to 76, followed by sequencing showed three distinct genotypes: one type associated with susceptible isolates, one type associated mostly with resistant isolates and one type found in a resistant isolate originating from South America. Three different zones could be defined according to the status of codon 76. For 50% inhibitory concentration values <=40nM (n=47), all isolates but one had K76 (wild type). For 50% inhibitory concentration values located between 40 and 60nM, isolates had either K76 (n=5) or K76T (mutant type) (n=6). For 50% inhibitory concentration values >60nM (n=88), all isolates had K76T. A lack of a strong association between the pfmdr1 N86Y mutation and in vitro chloroquine resistance was observed. Cg2 genotypes were less strongly linked than pfcrt genotypes with in vitro chloroquine susceptibility in isolates located below 40nM and above 60nM. Further studies are needed to determine the reliability of the pfcrt gene as a genetic marker for chloroquine resistance.