Genetic and Pathogenic Characteristics of an Emerging Lineage 7 PRRSV-2 (Prime Pac-Like) Strain in China

The emergence of the NADC30-like (Lineage1.8) porcine reproductive and respiratory syndrome virus (PRRSV) has accelerated the evolutionary divergence of PRRSV, causing significant economic losses to Chinese swine industry. In the present study, a novel Lineage 7 (L7/Prime Pac-like) PRRSV strain FJZHK-2025 was isolated in China. Full-length genome analysis revealed that FJZHK-2025 is closely related to L7 PRRSV and exhibits the highest nucleotide homology (96.4%-96.5%) with the L7 PRRSV reference strains. Notably, FJZHK-2025 contained a 36 amino acid (aa) insertion within Nsp2 that was identical to the Prime Pac PRRS vaccine strain. Phylogenetic analysis, recombination detection, and regional genomic homology comparisons revealed that FJZHK-2025 originated from inter-lineage recombination between L7 and lineage 1.8 (NADC30-like) PRRSV-2 strains. Animal challenge experiments showed that piglets infected with FJZHK-2025 developed a persistent high fever, displayed mild to moderate clinical symptoms and presented with moderate lung pathological lesions, indicating that the FJZHK-2025 strain is pathogenic to piglets. Therefore, it is critical to develop an effective strategy to prevent and control the spread of L7 PRRSV in China.