Antifolate resistance in Plasmodium falciparum: Multiple origins and identification of novel dhfr alleles

Background. Sulfadoxine-pyrimethamine has been widely used as first-line therapy for uncomplicated malaria throughout sub-Saharan Africa. Recent studies conducted in Asia and Africa suggest the triple-mutant dhfr genotype (51I/59R/108N) may have been generated as a single event in Southeast Asia, with subsequent spread of the single lineage to the African continent, but this hypothesis needs further validation. Methods. Direct sequencing of polymerase chain reaction (PCR) products, pyrosequencing, and cloning of PCR products were utilized to identify mutations in dhfr. To investigate the evolutionary history of dhfr alleles, we assayed microsatellite loci flanking dhfr along chromosome 4. Results. A total of 15 of 479 samples from western Kenya showed the presence of I164L, in 5 different genotypes. We document C50R in 2 of our samples. Using microsatellite markers, we show 2 haplotypes for both the 51I/ 108N/164L and 51I/59R/108N/164L genotypes. Our results also show multiple lineages for the triple-mutant dhfr genotype in Africa. Conclusions. These findings highlight the importance of local characterization of alleles before molecular surveillance of drug-resistant alleles is considered in different endemic settings and populations. © 2006 by the Infectious Diseases Society of America. All rights reserved.