Wide variation in microsatellite sequences within each Pfcrt mutant haplotype

Abstract

Flanking microsatellites for each of the Pfcrt mutant haplotype of Plasmodium falciparum remain conserved among geographical isolates. We describe here heterogeneity in the intragenic microsatellites among each of the Pfcrt haplotype. There were fourteen different alleles of AT repeats of intron 2 and eight alleles of TA repeats of intron 4 of the pfcrt gene among Indian isolates. This resulted in 33 different two-locus (intron 2 plus intron 4) microsatellite genotypes among 224 isolates. There were 15 different two-locus microsatellite genotypes within the South American Pfcrt haplotype (S₇₂V₇₃M₇₄N₇₅T₇₆S₂₂₀) and 11 genotypes in the southeast Asian haplotype (C₇₂V₇₃I₇₄E₇₅T₇₆S₂₂₀) in these isolates. Indian isolates with Pfcrt haplotype C₇₂V₇₃I₇₄E₇₅T₇₆S₂₂₀ shared one of its two-locus microsatellite genotype with southeast Asian P. falciparum parasite lines from Thailand (K1) and Indochina (Dd2 and W2). Conversely, Indian isolates containing S₇₂V₇₃M₇₄N₇₅T₇₆S₂₂₀ Pfcrt haplotype did not share any of their two-locus microsatellite genotype with South American parasite line 7G8 from Brazil. Significantly, large number of newer two-locus microsatellite genotypes were detected in a 2-year time period (P < 0.05). Microsatellite variation was more prominent in the areas of high malaria transmission. It is concluded that the genetic recombination in the intragenic microsatellites continues in the parasite population even after microsatellites flanking the pfcrt gene had already been fixed. Presence of various Pfcrt haplotypes and a variety of intragenic microsatellites indicates that there is a wide spectrum of chloroquine resistant parasite population in India. This information should be useful for malaria control programs of the country.