Molecular characterization and recombination analysis of porcine reproductive and respiratory syndrome virus emerged in southwestern China during 2012-2016

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important swine pathogen causing tremendous economic losses to the swine industry. To investigate the prevalence of PRRSV of genotype 2 (North American type, NA-type) in southwestern China, the Nsp2 hypervariable region (Nsp2 HV) and ORF5 of 61 PRRS viruses collected during 2012-2016 were sequenced and analyzed. All the virus detected clustered into the JXA1-like (52/61), VR-2332-like (7/61), and NADC30-like (2/61) sub-genotypes. Five deletions in Nsp2 HV were detected in addition to the typical 30aa discontinuous deletion in HP-PRRSV, and two of these five were not reported previously. Strikingly, two PRRS virus (SCnj16 and SCcd16) isolated in 2016 contained the classic HP-PRRSV molecular marker in the Nsp2-coding region, but belonged to the NADC30-like sub-genotype on the ORF5 gene. Further recombination and phylogenetic analysis on the two complete genomic sequences revealed that they may have originated from recombination events between the NADC30 and Chinese HP-PRRSV strains. The present study suggests that the endemic PRRSVs in the region have continuously evolved and new vaccine strategies are necessary for more efficient control of the virus.