MOLECULAR EPIDEMIOLOGY OF MALARIA IN YAOUNDE, CAMEROON-I - ANALYSIS OF POINT MUTATIONS IN THE DIHYDROFOLATE REDUCTASE-THYMIDYLATE SYNTHASE GENE OF PLASMODIUM-FALCIPARUM

Resistance to antifolate antimalarial drugs (cycloguanil, a biological ly active metabolite of proguanil, and pyrimethamine) is associated wi th a Ser-to Asn-108 point mutation in the dihydrofolate reductase-thym idylate synthase gene of Plasmodium falciparum. The frequency of this mutation was studied in 127 clinical isolates obtained in Yaounde, Cam eroon using a simple and rapid molecular technique based on the polyme rase chain reaction and restriction fragment length polymorphism. Of t he 127 isolates, pure wild-type Ser-108 codon, pure mutant-type Asn-10 8 codon, and mixed codons were observed in 66, 55, and six parasites, respectively. The proportion of antifolate-resistant, pure mutant-type codon, with respect to pure wild-type or mixed alleles, was 43% (55 o f 127). The results of the molecular assay were compared with those of semimicro isotopic in vitro assay in 34 isolates. All 17 pure Ser-108 isolates and two isolates with mixed alleles were sensitive to both p yrimethamine (50% inhibitory concentration [IC50] < 100 nM) and cyclog uanil (IC50 < 50 nM). Fourteen of 15 isolates with the mutant-type Asn -108 codon were resistant to pyrimethamine and cycloguanil. One isolat e viith Asn-108 showed a slightly elevated pyrimethamine IC50 (78 nM), which was within the sensitive range. This study provides further evi dence that antifolate-resistant P. falciparum isolates are already pre sent in Yaounde, Cameroon.