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 the gene for dihydrofolate reductase of Plasmodium falciparum containing codon 108, where a point mutation, causing a serine to asparagine change, occurs in pyrimethamine resistant parasites. The presence of the mutation was detected by restriction enzyme digestion. Parasites in blood samples collected from asymptomatic children before, and 3 weeks after, treatment with pyrimethamine-sulfadoxine or chlorproguanil-dapsone were analysed. Parasites in the samples taken at 3 weeks carried only the asparagine mutant.