Genomic characterization, pathogenicity, and PRRSV-vectored vaccine protection of an emerging recombinant PRRSV strain FJNP22-1

• Identification of a novel recombinant PRRSV strain (FJNP22-1), classified within PRRSV-2 Lineage 8 and Sub-lineage 1.8, with complex recombination events involving HP-PRRSV and NADC30-like strains. • FJNP22-1 exhibits high pathogenicity in piglets, causing 100% morbidity, severe clinical symptoms, and marked pulmonary lesions. • A recombinant PRRSV-vectored vaccine (rPRRSV-E2) provided strong protection against FJNP22-1 challenge, offering potential for improved PRRS control in China. Porcine reproductive and respiratory syndrome virus (PRRSV), the etiological agent of porcine reproductive and respiratory syndrome (PRRS), has caused substantial economic losses to the global swine industry. In recent years, frequent genetic recombination and mutation events in PRRSV have given rise to numerous genetic variants, presenting significant challenges for PRRS containment and eradication programs. In the present investigation, a novel PRRSV strain, designated FJNP22-1, was successfully isolated from an affected pig farm in Fujian Province, China, during a 2023 disease outbreak. Comprehensive phylogenetic analysis of the complete genome sequence identified FJNP22-1 as a member of Lineage 8 within the PRRSV-2. Notably, ORF5-based phylogenetic characterization revealed its classification within Sub-lineage 1.8 of PRRSV-2. Genomic recombination analysis revealed that FJNP22-1 was a recombination strain derived from HP-PRRSV (Lineage 8, major parental strain) and NADC30-like (Lineage 1, minor parental strain), with seven distinct recombination breakpoints identified across Nsp2, Nsp3, ORF2, and ORF4 gene regions. Pathogenicity evaluation demonstrated that FJNP22-1 infection induced 100% morbidity in piglets, with clinical manifestations including pyrexia, anorexia and severe growth retardation. Necropsy findings confirmed marked pulmonary lesions, supporting the conclusion that FJNP22-1 exhibits high pathogenicity in swine. Furthermore, a novel recombinant PRRSV-vectored vaccine candidate (rPRRSV-E2), engineered via reverse genetics to express the classical swine fever virus (CSFV) E2 glycoprotein, conferred robust protection against FJNP22-1 challenge in piglets. This study enhances our understanding of PRRSV molecular epidemiology and provides valuable insights for vaccine development and PRRS control strategies in China.