Tracking Origins and Spread of Sulfadoxine-Resistant Plasmodium falciparum dhps Alleles in Thailand

Abstract

The emergence and spread of drug-resistant Plasmodium falciparum have been a major impediment for the control of malaria worldwide. Earlier studies have shown that similar to chloroquine (CQ) resistance, high levels of pyrimethamine resistance in P. falciparum originated independently 4 to 5 times globally, including one origin at the Thailand-Cambodia border. In this study we describe the origins and spread of sulfadoxineresistance-conferring dihydropteroate synthase (dhps) alleles in Thailand. The dhps mutations and flanking microsatellite loci were genotyped for P. falciparum isolates collected from 11 Thai provinces along the Burma, Cambodia, and Malaysia borders. Results indicated that resistant dhps alleles were fixed in Thailand, predominantly being the SGEGA, AGEAA, and SGNGA triple mutants and the AGKAA double mutant (mutated codons are underlined). These alleles had different geographical distributions. The SGEGA alleles were found mostly at the Burma border, while the SGNGA alleles occurred mainly at the Cambodia border and nearby provinces. Microsatellite data suggested that there were two major genetic lineages of the triple mutants in Thailand, one common for SGEGA/SGNGA alleles and another one independent for AGEAA. Importantly, the newly reported SGNGA alleles possibly originated at the Thailand-Cambodia border. All parasites in the Yala province (Malaysia border) had AGKAA alleles with almost identical flanking microsatellites haplotypes. They were also identical at putatively neutral loci on chromosomes 2 and 3, suggesting a clonal nature of the parasite population in Yala. In summary, this study suggests multiple and independent origins of resistant dhps alleles in Thailand.

Evolution of Plasmodium falciparum drug resistance: implications for the development and containment of artemisinin resistance

“…Previous molecular evolutionary study had shown that only two lineages of high sulfadoxine resistance (parasites harboring three or four substitutions in DHPS) were observed in Cambodia (38). These two lineages were also found in Thailand (40). A large-scale study in Africa has shown that only five resistant lineages were observed in mild-to moderate-resistant parasites (parasites harboring one or two substitutions in DHPS) (69).…”

“…An Ala-to-Gly substitution at position 437 (encoding DHPS with amino acid sequences SGKAA at positions 436, 437, 540, 581, and 613, where the altered residue is underlined) has been proposed as the first step to sulfadoxine resistance (13,38,39). Triple-mutant DHPS enzymes (AGEAA, SGEGA, and SGNGA) demonstrate the highest levels of sulfadoxine resistance in the natural parasite populations, and parasites encoding quadruple-mutant DHPS enzymes have been detected (at rare frequencies) in some places in Southeast Asia (13,38,40).…”

“…Several recent studies on dhps alleles and microsatellite haplotypes closely linked to the dhps gene have revealed the putative geographical origins and spread of sulfadoxine-resistant P. falciparum isolates (11,13,38,40,68,69) (Fig. 5C).…”

Multiple Origins of Plasmodium falciparum Dihydropteroate Synthetase Mutant Alleles Associated with Sulfadoxine Resistance in India

“…In South America, there is a prevalence of the triple mutant SGEGA allele (16). Triple mutant alleles AGEAA and SGEGA, along with novel triple mutant allele SGNGA, are prevalent in Thailand and Cambodia (4,33). In India, the prevalence of different mutant dhps alleles varies from region to region (1,3,11), due to different rates of malaria transmission and level of drug resistance (10).…”

Advanced Molecular Detection of Malarone Resistance

“…Molecular tools that can detect resistant alleles have been useful in population-based studies in tracking resistant parasites in countries where malaria is endemic. The detection of molecular markers of resistance has historically involved various PCR-based genotyping methods, such as sequence-specific PCR amplification, pyrosequencing, and Sanger sequencing of a genomic region containing one or more resistance mutations (1)(2)(3)(4). One major limitation of these conventional genotyping methods is their detection limit of minor allele frequencies (MAFs).…”