Abstract: Porcine reproductive and respiratory syndrome virus (PRRSV), comprising two distinct species, PRRSV-1 (European genotype) and PRRSV-2 (North American genotype), exhibits significant genetic variability and poses a substantial threat to global swine production. In this study, a PRRSV-1 strain, designated GZ0308, was isolated from the lung tissue of infected piglets on a farm in Guizhou Province using porcine alveolar macrophages (PAMs). The complete genome of GZ0308 spans 14 970 nucleotides, displaying 86.99% nucleotide identity with the PRRSV-1 reference strain LV and 66.49% with the PRRSV-2 strain VR2332. Phylogenetic analysis positioned GZ0308 within a novel branch of PRRSV-1 subtype 1. Comparative genomic analysis revealed that GZ0308 harbors 43 discontinuous amino acid deletions in the NSP2 coding region and a 5-amino-acid deletion in the overlapping region of ORF3 and ORF4 relative to the LV strain. To assess pathogenicity, five-week-old piglets were inoculated intramuscularly and intranasally with 2 mL of viral suspension (10^5.5TCID₅₀·mL^-1 per route). Compared to the control group, GZ0308-infected piglets exhibited transient pyrexia, lethargy, and a significant reduction in average daily weight gain. Postmortem examination identified characteristic diffuse interstitial pneumonia lesions, confirming the strain’s pathogenicity in piglets. These findings contribute novel data to the molecular epidemiology of PRRSV in China and underscore the need for continued surveillance of emerging PRRSV variants.

Key words: PRRSV, the European type, molecular characteristics, pathogenicity