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Chulalongkorn Medical Journal

Abstract

Problem/background : Allele-specific amplification is an important tool for a largescale study of geographic distribution of pathogens harboringpolymorphic genes. In this study, we have developed a simplemethod to differentiate strains of Plasmodium falciparum basedon polymorphic block 2 located at the 5’ portion of the merozoitesurface protein-1 gene (PfMsp-1). Block 2 of PfMsp-1, a strongcandidate for asexual blood-stage vaccine, contains 3 basicsequence types with MAD20 type, K1 type and RO33 type asrepresentative alleles.Objective : To develop a polymerase chain reaction (PCR) method capableof detecting PfMsp-1 genotypes.Design : Experimental study.Setting : Department of Parasitology, Faculty of Medicine, ChulalongkornUniversity.Materials and Methods : The method deployed semi-nested PCR targeting allelespecificsequences of each representative type of blocks2 of PfMsp-1. The performance of the method was evaluatedwith 50 P. falciparum blood samples collected from patients inChanthaburi, Tak and Yala provinces.Results : The method is sensitive to detect as few as 5 parasites inthe samples whereas specific alleles of block 2 could beunequivocally determined. Minor parasite populations inthe isolates containing multiple clone infections were detectedby the method. Of the 50 P. falciparum isolates examined,MAD20, K1 and RO33 allelic types were identified in 28, 14and 8 samples by the PCR genotyping method, respectively.Multiple clone infections were observed in 4 of these isolates.Conclusion : The PCR genotyping method developed in this study isapplicable for large-scale population genetic analysis ofP. falciparum population based on the PfMsp-1 locus.

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