Genetic complexity of Plasmodium vivax infections in Sri Lanka, as reflected at the merozoite-surface-protein-3a locus

Abstract

The presence of genetically different strains of malarial parasites in cases of human malaria is a severe drawback in the successful control of the disease. In Sri Lanka, although this species accounts for 60%–80% of all of the cases of clinical malaria that occur each year, the genetic complexity of Plasmodium vivax on the island remains to be elucidated. In recent studies based on PCR–RFLP and the parasites’ merozoite-surface-protein-3a locus, the genetic structure of 201 clinical isolates of P. vivax, from two malaria-endemic areas and a non-endemic area of the island, was investigated. Although the PCR only produced amplicons of three sizes [1900 (72.6%), 1500 (25.9%) and 1200 (1.5%) bp], the RFLP analysis based on HhaI orAluI digestion yielded 22 and 26 restriction patterns, respectively, with 51 combined patterns recorded. The distribution of the prominent PCR–RFLP haplotypes was area-specific. The probability that an investigated case had a multiple-clone infection (MCI) was higher among the cases from the endemic areas (20.0%) than among those from the non-endemic area (13.8%) but this difference was not statistically significant. Since 17 single-clone isolates produced only 11 different PCR–RFLP haplotypes but (after sequencing) 13 distinct nucleotide haplotypes, it is clear that the results of the PCR–RFLP were not revealing all of the diversity that existed at the nucleotide level. Four mass blood surveys in a malaria-endemic area demonstrated that seasonal changes in the prevalences of human infection with P. vivax may influence the occurrence of MCI.