A RFLP 1-4-3 L1C Variant of PRRSV-2 Isolated in Sichuan Province, China: Genetic Characterization and Pathogenicity.

Porcine reproductive and respiratory syndrome virus (PRRSV), known for causing reproductive disorders in sows and respiratory issues in piglets, poses a significant threat to the global swine industry. Since its initial report in 2013, the L1C (lineage 1.8/NADC30-like) PRRSV has drawn significant attention in China due to its high recombination potential and diverse pathogenicity. This study focuses on a naturally occurring recombinant L1C variant, SCABTC-202302, characterized by an restriction fragment length polymorphism (RFLP) pattern of 1-4-3. We investigate the strain's genetic evolution, recombination, pathogenicity, and immune and antibody responses. Phylogenetic analysis of the ORF5 (open reading frame) gene classified the SCABTC-202302 strain as lineage 8.7, while whole-genome analysis categorized it as L1C. Notably, a discontinuous deletion of 131 amino acids (AAs) was observed in the NSP2 gene, along with specific AA mutations in ORF5. Recombination analysis revealed the NADC30 strain as the primary parent, with contributions from the JXA1 strain in the ORF2-ORF7 region. The strain caused lung and lymph node damage, sustained high-level viremia, and elevated inflammatory factors in infected piglets. Our study provides valuable insights into the genetic characteristics, pathogenicity, and immunological profile of L1C strains, contributing to the development of vaccines and control measures for PRRSV.