Whole Genome Characterization and Pathogenicity of a SC2020-1-Like PRRSV-1 Strain Emerging in Southwest China.

Porcine reproductive and respiratory syndrome virus (PRRSV), encompassing PRRSV-1 and PRRSV-2, significantly impacts the global pig industry by causing reproductive disorders and respiratory difficulties. In this paper, we isolated a novel PRRSV-1 strain, named SCPJ2023, from weaned piglets in Sichuan. Utilizing primary macrophages, we isolated SCPJ2023 and performed complete genome sequencing through metagenomic analysis. Phylogenetic analysis classified SCPJ2023 as pan-European subtype 1. SCPJ2023 showed a 95.3% similarity to SC2020-1. Amino acid analysis identified differences in Nsp2, GP3, and GP4 between SCPJ2023 and other representative strains. In vivo challenge experiments demonstrated that SCPJ2023 induced clinical symptoms in piglets, including coughing, fever, reduced appetite, and depression. Pathological examinations revealed hemorrhage and congestion, increased inflammatory cells, thickening of the alveolar wall, and collapse of the alveolar cavity in SCPJ2023-infected piglets. Altogether, our study identified a novel pathogenic isolate of PRRSV-1, expanding the newly named SC2020-1-like subgroup by identifying additional strains beyond the initial SC2020-1 isolate.