Characterization and Pathogenicity of a Porcine Reproductive and Respiratory Syndrome Virus Strain with Strong Homology to a HP‐PRRSV Vaccine Strain in the Field

Abstract

A PRRSV strain, PRRSV2/CN/FJLX06/2021, with strong homology to an MLV‐like strain HeN1201 that evolved from the highly pathogenic PRRSV vaccine virus HuN4‐F112, was isolated from a dying piglet in China. BLAST and phylogenetic analyses showed that PRRSV2/CN/FJLX06‐2021 was most closely related to HeN1201 and HuN4 (the parental strain of MLV HuN4‐F112) and clustered with Chinese HP‐PRRSV strains in PRRSV‐2 lineage 8.7. Importantly, 29 of the 39 characteristic amino acid mutations in the HuN4‐F112 genome were found at the corresponding sites of PRRSV2/CN/FJLX06‐2021. Animal studies showed that piglets infected with PRRSV2/CN/FJLX06‐2021 had a persistent high fever, higher viremia, presence of interstitial pneumonia, and a higher mortality rate (40%) within 2 weeks than those vaccine‐inoculated with HuN4‐F112. Taken together, these data suggest that PRRSV2/CN/FJLX06‐2021 is an MLV‐like strain that has evolved from MLV HuN4‐F112 and is highly pathogenic to piglets.