Ordered Accumulation of Mutations Conferring Resistance to Sulfadoxine-Pyrimethamine in the Plasmodium falciparum Parasite

BACKGROUND: Monitoring the prevalence of drug resistant Plasmodium falciparum is essential for effective malaria control. Resistance to pyrimethamine and sulfadoxine increases as mutations accumulate in the parasite genes encoding dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps), respectively. Although parasites are exposed to these antifolate drugs simultaneously, it remains virtually unknown whether dhfr and dhps mutations accumulate along interrelated paths. METHODS: We investigated the order of step-wise accumulation in dhfr and dhps by cumulative analyses using binomial tests in 575 P. falciparum isolates obtained from 7 countries in Asia and Melanesia. RESULTS: An initial step in the accumulation of mutations preferentially occurred in dhfr (2 mutations), followed by 1 mutation in dhps. In a subsequent step, mutations were estimated separately for…