Characterization and pathogenicity of single-farm-isolated PRRSV 1 and PRRSV 2 strain in China

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major threat to the swine industry globally. In China, the dominance of PRRSV 2 is complicated by the emergence and co-circulation of genetically distinct strains, including a rising number of PRRSV 1 cases. In this study, the concurrent circulation of PRRSV 1 and PRRSV 2 was identified, and two novel strains AHB1 and Chah2022 were isolated from a single sow farm experiencing reproductive failure. Genetic analysis revealed that AHB1 shared 81.6%-83.6% nucleotide identity with subtype 1 strains of PRRSV 1 and clustered within a new evolutionary branch, characterized by a continuous 54-amino acid deletion in nsp2 and 1-amino acid deletion in the GP3-GP4 overlap region. In contrast, Chah2022 was identified as a recombinant virus with NADC30-like (lineage 1) and highly pathogenic PRRSV-like (lineage 8) strains. Pathogenicity assessment in nursery piglet model demonstrated that both AHB1 and Chah2022 had established systemic and persistent infections, although with low or moderate clinical signs. Our findings provide the evidence of PRRSV 1 and PRRSV 2 concurrent circulation in the single sow farm in China, which highlights the ongoing evolution of both Chinese PRRSV species and underscores the urgent need for enhanced surveillance and updated control strategies.