High prevalence of the 437G mutation associated with sulfadoxine resistance among Plasmodium falciparum clinical isolates from Iran, three years after the introduction of sulfadoxine-pyrimethamine.

OBJECTIVE: The objective of this study was to determine the frequency of dhfr and dhps resistance-associated haplotypes in Plasmodium falciparum isolates, three years after the introduction of sulfadoxine-pyrimethamine (SP) as the first-line antimalarial treatment in Iran.
METHODS: Blood samples (N=182) were collected from patients presenting with falciparum malaria from southeastern Iran, and analyzed by nested-PCR/restriction fragment length polymorphism, followed by sequencing analysis.
RESULTS: In pfdhfr, double mutation at positions 59R and 108N was a predominant allele with a prevalence of 95.7%. The pure double mutations of pfdhfr (I(51)N(108)) were detected, and showed an increase from 0.7% to 4.3% after the introduction of SP as first-line drug. Furthermore, a significant decrease in double mutations/wild-type of pfdhfr/pfdhps (R(59)N(108)/A(437)) was observed from 2004 (83.5%) to 2008 (44%) after changes in treatment policy. With regards to pfdhps, the results showed a rapid increase in frequency of the single pure form of pfdhps at position 437G (54.4%) and that of triple pfdhfr/pfdhps (R(59)N(108)/G(437)) mutant haplotype (51.7%) after three years.
CONCLUSIONS: The absence of quintuple mutations in the examined isolates supports the continued use of SP as the treatment of choice for uncomplicated malaria as a partner drug to artemisinin combination therapy in Iran. However, the increase in the triple pfdhfr/pfdhps (R(59)N(108)/G(437)) mutant haplotypes indicates that the P. falciparum parasite populations have the potential to evolve into dhfr/dhps quintuple mutants in the near future. Therefore, monitoring the status of dhps alleles as a predictor of the development of clinical resistance to sulfadoxine should be a high priority in this region.