Independent evolution of porcine reproductive and respiratory syndrome virus 2 with genetic heterogeneity in antigenic regions of structural proteins in Korea.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen that affects the global swine industry. The continuous evolution of this virus has made control and prevention difficult, which emphasizes the importance of monitoring currently circulating PRRSV strains. In this study, we investigated the genetic characteristics of whole structural genes of 35 PRRSV-2 isolates that circulated between 2012 and 2017 in Korea. Genetic and phylogenetic analysis demonstrated that a recently identified PRRSV-2 shared a relatively low level of nucleotide sequence identity that ranged from 86.2% to 92.8%; however, they were clustered into four distinct Korean field clades, except KU-N1702, in ORF2-7-based phylogeny. KU-N1702 was closely related to the NADC30-like strains that were identified in the USA and China. Amino acid sequence analysis showed that the GP5 neutralizing epitope was conserved among the KU viruses. In contrast, the viruses had genetic mutations in key residues for viral neutralization within GP5 and M. For minor structural proteins, neutralizing epitopes, aa 41-55 of GP2, 61-75 of GP3, and 51-65 of GP4, were variable among the KU viruses. Bioinformatics demonstrated diversifying evolution within the GP2 and GP4 neutralizing epitopes and the emergence of a novel glycosylation site within the GP3 and GP4 neutralizing epitopes. Taken together, these data provide evidence that Korean PRRSV-2 evolved independently in Korea, with genetic heterogeneity in antigenic regions of structural proteins.