POINT MUTATIONS IN THE DIHYDROFOLATE-REDUCTASE AND DIHYDROPTEROATE SYNTHETASE GENES AND IN-VITRO SUSCEPTIBILITY TO PYRIMETHAMINE AND CYCLOGUANIL OF PLASMODIUM-FALCIPARUM ISOLATES FROM PAPUA-NEW-GUINEA

Plasmodium falciparum isolates from 24 Papua New Guinean patients with symptomatic malaria were tested for susceptibility to pyrimethamine a nd cycloguanil. Thirteen isolates were sensitive to both agents and th e remainder exhibited varying degrees of resistance. No isolates were found to be resistant to one agent yet sensitive to the ether and a po sitive correlation suggesting cross-resistance was found. Parasite DNA extracted from the patients' stained blood slides was amplified and s equenced to examine point mutations in the dihydrofolate reductase (DH FR) and dihydropteroate synthetase genes (DHPS) associated with antifo late resistance. All resistant isolates possessed mutations in the DHF R gene at codon 108, the majority changing from Ser to Asn, but one is olate from Ser to Thr, a change not previously reported in field isola tes. A second mutation of the DHFR gene at Cys-59 to Arg was present i n isolates with higher level resistance, but not exclusively so. Seque ncing the DHPS gene, as a predictor of sulfadoxine resistance, reveale d only one example that was different from DHPS alleles of sensitive i solates.