Diversity of vir Genes in Plasmodium vivax from Endemic Regions in the Republic of Korea: an Initial Evaluation

Abstract

Variant surface antigens (VSAs) encoded by pir families are considered to be the key proteins used by many Plasmodium spp. to escape the host immune system by antigenic variation. This attribute of VSAs is a critical issue in the development of a novel vaccine. In this regard, a population genetic study of vir genes from Plasmodium vivax was performed in the Republic of Korea (ROK). Eighty-five venous blood samples and 4 of the vir genes, namely vir 27, vir 21, vir 12, and vir 4, were selected for study. The number of segregating sites (S), number of haplotypes (H), haplotype diversity (Hd), DNA diversity (π and Θ_w), and Tajima's D test value were conducted. Phylogenetic trees of each gene were constructed. The vir 21 (S=143, H=22, Hd=0.827) was the most genetically diverse gene, and the vir 4 (S=6, H=4, Hd=0.556) was the opposite one. Tajima's D values for vir 27 (1.08530, P>0.1), vir 12 (2.89007, P<0.01), and vir 21 (0.40782, P>0.1) were positive, and that of vir 4 (-1.32162, P>0.1) was negative. All phylogenetic trees showed 2 clades with no particular branching according to the geographical differences and cluster. This study is the first survey on the vir genes in ROK, providing information on the genetic level. The sample sequences from vir 4 showed a clear difference to the Sal-1 reference gene sequence, whereas they were very similar to those from Indian isolates.

Keywords: Plasmodium vivax; genetic diversity; the Republic of Korea; vir gene.

Fig. 1

Blood collection regions. From left to right, Gimpo (GP), Paju (PJ), and Choerwon (CW) are denoted by asterisks.

Fig. 2

Sequence polymorphism of vir genes in the ROK P. vivax isolates. The polymorphic nucleotides were compared to that of Sal-1 (GenBank no.: AAKM01000041.2). (A) Sequences of vir 27 gene of isolates. (B) Sequences of vir 21 gene of ROK isolates compared with 5 Indian isolates. (C) Sequences of vir 12 gene of isolates. (D) Sequences of vir 4 gene of ROK and Indian isolates. The listed sequences are indicated by dots for identical nucleotides with sequences of Sal-1, and hyphens for gaps. The locations of polymorphic sites are represented above and the nucleotide changes are marked with colors.

Fig. 3

The phylogenetic tree of vir 4 was inferred using the minimum evolution method. The optimal tree with the sum of branch length=0.00535425 is shown.