Molecular surveillance of Plasmodium vivax dhfr and dhps mutations in isolates from Afghanistan

Analysis of dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) mutations in Plasmodium vivax wild isolates has been considered to be a valuable molecular approach for mapping resistance to sulphadoxine-pyrimethamine (SP). The present study investigates the frequency of SNPs-haplotypes in the dhfr and dhps genes in P. vivax clinical isolates circulating in two malaria endemic areas in Afghanistan.

P. vivax clinical isolates (n = 171) were collected in two different malaria endemic regions in north-west (Herat) and east (Nangarhar) Afghanistan in 2008. All collected isolates were analysed for SNP-haplotypes at positions 13, 33, 57, 58, 61, 117 and 173 of the pvdhfr and 383 and 553 of the pvdhps genes using PCR-RFLP methods.

All 171 examined isolates were found to carry wild-type amino acids at positions 13, 33, 57, 61 and 173, while 58R and 117N mutations were detected among 4.1% and 12.3% of Afghan isolates, respectively. Based on the size polymorphism of pvdhfr genes at repeat region, type B was the most prevalent variant among Herat (86%) and Nangarhar (88.4%) isolates. Mixed genotype infections (type A/B and A/B/C) were detected in only 2.3% (2/86) of Herat and 1.2% (1/86) of Nangarhar isolates, respectively. The combination of pvdhfr and pvdhps haplotypes among all 171 samples demonstrated six distinct haplotypes. The two most prevalent haplotypes among all examined samples were wild-type (86%) and single mutant haplotype I13P33F57S58T61N 117I173/A383A553 (6.4%).Double (I13P33S57R58T61N117I173/A383A553) and triple mutant haplotypes (I13P33S57R 58T61N117I173/G383A553) were found in 1.7% and 1.2% of Afghan isolates, respectively. This triple mutant haplotype was only detected in isolates from Herat, but in none of the Nangarhar isolates.

The present study shows a limited polymorphism in pvdhfr from Afghan isolates and provides important basic information to establish an epidemiological map of drug-resistant vivax malaria, and updating guidelines for anti-malarial policy in Afghanistan. The continuous usage of SP as first-line anti-malarial drug in Afghanistan might increase the risk of mutations in the dhfr and dhps genes in both P. vivax and Plasmodium falciparum isolates, which may lead to a complete SP resistance in the near future in this region. Therefore, continuous surveillance of P. vivax and P. falciparum molecular markers are needed to monitor the development of resistance to SP in the region.