Genetic diversity of the malaria vaccine candidate merozoite surface protein 1 gene of Plasmodium vivax field isolates in Republic of Korea

The Plasmodium vivax merozoite surface protein 1 (Pvmsp-1) locus codes for a major asexual blood-stage antigen currently proposed as a malaria vaccine candidate antigen. However, extensive polymorphism of this protein has been observed in isolates from different geographical areas. Here, we investigate the extent and the frequency of allelic diversity at the Pvmsp-1 locus in field isolates collected in the Republic of Korea during the past decade. Among the 45 Korean isolates, six Pvmsp-1 gene types (SKOR-I to SKOR-VI) were identified as unique combinations of type sequences in each variable block. Of these six different Pvmsp-1 gene types, two major Pvmsp-1 allelic types were found in 72% (SKOR-I) and 28% (SKOR-II) of field isolates collected in 1996 to 2000, and four different allelic types (SKOR-III to SKOR-VI) emerged in 70% (10-25%) of isolates collected in 2007 to 2009. These results suggest that allelic diversity of Pvmsp-1 increased in several variable regions, including the N- and C-terminals, after reemergence of P. vivax parasites in the Republic of Korea.