Nucleotide sequence analysis of Vietnamese highly pathogenic porcine reproductive and respiratory syndrome virus from 2013 to 2014 based on the NSP2 and ORF5 coding regions

A total of 34 highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) strains isolated from Vietnam during 2013-2014 were sequenced and analyzed. A partial sequence of ORF1a corresponding to the nonstructural protein 2 (Nsp2) coding region and the full sequence of open reading frame 5 (ORF5) gene was used for the analysis. The HP-PRRSV strains were isolated from pig herds that had never been vaccinated for PRRSV. Nucleotide sequence identities in the portions of ORF1a corresponding to the nonstructural protein 2 (Nsp2) coding region and ORF5 ranged from 96.4 to 100 % and 83.2 to 100 %, respectively. All of the 34 Vietnamese HP-PRRSV strains showed two discontinuous 30-amino-acid deletions in the Nsp2 coding region as a genetic marker of prototypic Chinese HP-PRRSV. The amino acid arginine (R) was present at positions 13 and 151 in ORF5 in 29 out of 34 Vietnamese HP-PRRSV isolates, as well as in the prototypic Chinese HP-PRRSV. Sequence analysis of the ORF5 genes of all Vietnamese HP-PRRSVs revealed six subgroups: Viet 1 to 4, JAX1-like, and VR-2332-like. Nucleotide and amino acid sequence analysis of 34 Vietnamese HP-PRRSV isolates from 2013-2014 indicated that Vietnamese HP-PRRSV has undergone rapid evolutionary changes in recent years when compared with Vietnamese HP-PRRSV isolated before 2012.