A molecular analysis of European porcine reproductive and respiratory syndrome virus isolated in South Korea

In a situation where European genotype of porcine reproductive and respiratory syndrome virus (PRRSV) has recently emerged in South Korea, this study aims to understand variations in and relatedness among 25 European (EU) genotype 1 PRRSV isolates obtained from Korean pig farms during the period ranging from 2006 to 2009 for their sequences of nonstructural protein 2 (NSP2), open reading frames (ORF) 5 and 7, which, in turn, were compared with those of published Korean type 1 PRRSV isolates (CP6874, IV3140 and KNU07) and other EU PRRSV strains. The sequence data revealed that all Korean type 1 isolates were found to possess notable 19 amino acid deletions within NSP2 between positions 748 and 766. Based on the complete ORF5 sequences, the results showed that the Korean isolates amounted to 82.0-99.5% in amino acid identity with one another, while sharing a lower level of amino acid identity ranging from 71.6% to 92.0% with EU genotype strains isolated in other geographic areas. According to an amino acid sequence comparison of ORF7, the level of identity among the Korean type 1 isolates was found to range from 86.7% to 100%. Phylogenetic analyses based on ORF5 and ORF7 sequences indicated that the Korean type 1 isolates belonged to the pan-European subtype 1; in ORF5 phylogeny, they form three distinct clusters from other EU genotype PRRSV strains. In conclusion, those findings suggest that the Korean type 1 PRRSV may have undergone a high degree of variations since EU genotype virus was first detected.