Molecular epidemiological analysis of the antigen diversity of Plasmodium vivax and P.falciparum

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The diversity of surface antigens of Plasmodium vivax and P.falciparum was studied at the genetic on level field isolates from endemic areas of Thailand and Vietnam. Analysis of more than 300 isolates by PCR and DNA sequencing revealed the followings.1.Polymorphism of the merozoite surface antigen (MSP1) gene of P.vivax : 15 Thai isolates possessed 35 permutations in the regions from ICB5 to ICB6, most of which were dimorphic substitutions. Two types of recombination bwtween type 1 and type 2 sequences were found in a polymorphic region. These results suggest that allelic diversity may be generated by recombination as found for the P.falciparum MSP1 gene.2.Polymorphism of the merozoite surface antigen (MSP1) gene of P.falciparum : A PCR system, which identifies up to 24 different MSP1 gene types per isolate, was developed by using primers specific for allelic type sequences. In total, 17 to 21 different MSP1 gene types were identified in Vietnam and Thailand, respectively. Frequency distribution of MSP1 gene type differed significantly between the two areas. The F st analysis indicated significant divergence in variable blocks of MSP1 except block 2 between Thai and Vietnam isolates. Linkage analysis between variable blocks localized regions in the gene for frequent recombination (block 4) and less frequent recombination (blocks 3 and 5) as well as no recombination (blocks 6-16). Furthermore, Thai isolates showed 2 new polymorphic residues in the C terminus, 19 kD region of MSP1.3.Sequencing of the thrombospondin-related anonymous protein (TRAP) gene of P.falciparum of 20 Thai isolates showed variations specific for Thai isolates and also suggested recombination in the gene.