Multiple origins of Plasmodium falciparum dihydropteroate synthetase mutant alleles associated with sulfadoxine resistance in India

Abstract

With the spread of Chloroquine (CQ) resistant malaria in India, Sulfdoxine - Pyrimethamine (SP) alone or in combination with Artesunate is used as an alternative antimalarial drug. Due to continuous drug pressure, the Plasmodium falciparum parasite is exhibiting resistance to antifolates because of mutations in candidate genes dihydrofolate reductase (dhfr) and dihydropteroate synthetase (dhps). Our earlier study on flanking microsatellite markers of dhfr mutant alleles from India had shown single origin of the pyrimethamine resistance, with some minor haplotypes, which shared haplotypes with South East Asian (Thailand) strains. In the present study, we have analyzed 193 of these Indian P.falciparum isolates for 15 microsatellite loci around dhps to investigate the genetic lineages of the mutant dhps alleles in different part of the country. Eighty one of these samples had mutant dhps alleles, of which 62 were from Andaman and Nicobar Islands and remaining 19 from mainland India. Of 112 wild type dhps allele, 109 were from mainland India and only 3 from Andaman and Nicobar Islands. Consistent with the model of selection, the mean expected heterozygosity (H_e) around mutant dhps alleles (H_e= 0.55; n=81) associated with sulfadoxine resistance was lower (P≤ 0.05) compared to the mean H_e around wild type dhps allele (H_e=0.80; n=112). There was more genetic diversity in flanking microsatellites of dhps than dhfr among these isolates which confirms the assertion that dhps mutations are at a very early stage of fixation in parasite population. Microsatellite haplotypes around various mutant dhps alleles suggests that the resistant dhps alleles have multiple independent origins in India, especially in Andaman and Nicobar Islands. Determining the genetic lineages of the resistant dhps alleles on the Andaman and Nicobar Islands and mainland India is significant given the role of Asia in the intercontinental spread of chloroquine and pyrimethamine resistant parasite in the past.