A novel recombinant porcine reproductive and respiratory syndrome virus with significant variation in cell adaption and pathogenicity

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that causes huge economic losses to the swine industry worldwide. In this study, a type 2 PRRSV strain was isolated from primary porcine alveolar macrophage cells and designated as GD1404. Interestingly, this strain was unable to grow in MARC-145 cells. Analysis of the full-length genome sequence revealed that strain GD1404 was an inter-sub genotype recombinant of strains QYYZ and DCAl. The C-terminus of the GP2 protein of strain GD1404 had an amino acid deletion. Also, the ORF5a protein had 51 codons, five more than most other highly pathogenic (HP-PRRSV) strains. Phylogenetic analysis based on ORF5 gene sequences showed that strain GD1404 and five others isolated in China formed a new subgenotype represented by strain QYYZ. Challenge experiments with piglets showed that the GD1404 and HP-PRRSV BB0907 strains caused similar rates of mortality and interstitial pneumonia. However, strain GD1404 infection resulted in lower viremia and viral loads in the lungs, as compared with strain BB0907. The results of this study provide evidence of the circulation of type 2 PRRSV QYYZlike strains in China with variations in cell adaption and pathogenic abilities.