Molecular characterization and pathogenicity of a HP-like PRRSV strain and a NADC30 recombinant strain.

Porcine Reproductive and Respiratory Syndrome Virus Type 2 (PRRSV-2) remains widespread in China and continues to persist as an important pathogen affecting the swine industry. In recent years, NADC30-like strains and their recombinants have become dominant, while HP-PRRSV strains are mostly sporadic, resulting in ongoing outbreaks and considerable economic losses. This study successfully isolated two PRRSV-2 strains from Hunan and Shandong, and assessed their pathogenicity in swine. Phylogenetic analysis identified that the strain HUN/2022/F2 is classified under Sublineage 8.7, sharing a high degree of sequence homology with HP-PRRSV strains. The strain SDLY/2023/01 is situated within Lineage 1, exhibiting a high degree of homology with NADC30-like strains. Recombination analysis revealed the absence of recombination events in HUN/2022/F2. However, SDLY/2023/01 was determined to be a recombinant strain originating from NADC30, JXA1, and VR2332. Animal challenge experiments indicated that HUN/2022/F2 manifests moderate pathogenicity in piglets, as evidenced by symptoms such as fever, weight loss, and lesions in the lungs and spleen, though without resultant mortality. In contrast, SDLY/2023/01 induced only mild clinical symptoms, suggesting low pathogenicity. These findings underscore the differential pathogenicity among PRRSV strains across various lineages. This study contributes valuable insights for the epidemiological surveillance of PRRSV.