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 biologically active metabolite of proguanil, and pyrimethamine) is associated with a Ser- to Asn-108 point mutation in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum. The frequency of this mutation was studied in 127 clinical isolates obtained in Yaounde, Cameroon using a simple and rapid molecular technique based on the polymerase chain reaction and restriction fragment length polymorphism. Of the 127 isolates, pure wild-type Ser-108 codon, pure mutant-type Asn-108 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 of 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 pyrimethamine (50% inhibitory concentration [IC50] < 100 nM) and cycloguanil (IC50 < 50 nM). Fourteen of 15 isolates with the mutant-type Asn-108 codon were resistant to pyrimethamine and cycloguanil. One isolate with Asn-108 showed a slightly elevated pyrimethamine IC50 (78 nM), which was within the sensitive range. This study provides further evidence that antifolate-resistant P. falciparum isolates are already present in Yaounde, Cameroon.
Basco
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LK
Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Organisation de Coordination pour la lutte contre les Endemies en Afrique Centrale, Yaounde, Cameroon.
Ringwald
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P
D000483:Alleles; D000818:Animals; D002163:Cameroon / Q000453:epidemiology; D003062:Codon / Q000235:genetics; D016054:DNA, Protozoan / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D004351:Drug Resistance / Q000235:genetics; D017125:Genes, Protozoan / Q000235:genetics; D006801:Humans; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000469:parasitology; D017720:Molecular Epidemiology; D010963:Plasmodium falciparum / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D013940:Thymidylate Synthase / Q000235:genetics*
D003062:Codon; D016054:DNA, Protozoan; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase