DIRECT EVIDENCE THAT ASPARAGINE AT POSITION-108 OF THE PLASMODIUM-FALCIPARUM DIHYDROFOLATE-REDUCTASE IS INVOLVED IN RESISTANCE TO ANTIFOLATE DRUGS IN TANZANIA

A nested polymerase chain reaction was used to amplify a fragment of t he gene for dihydrofolate reductase of Plasmodium falciparum containin g codon 108, where a point mutation, causing a serine to asparagine ch ange, occurs in pyrimethamine resistant parasites. The presence of the mutation was detected by restriction enzyme digestion. Parasites in b lood samples collected from asymptomatic children before, and 3 weeks after, treatment with pyrimethamine-sulfadoxine or chlorproguanil-daps one were analysed. Parasites in the samples taken at 3 weeks carried o nly the asparagine mutant.