Novel characterization of NADC30-like and NADC34-like PRRSV strains in China: epidemiological status and pathogenicity analysis of L1A variants1

NADC34-like Porcine reproductive and respiratory syndrome virus (PRRSV), which first appeared in China in 2017, is currently one of the main epidemic strains in China. In this study, we found that a new variant of NADC34-like PRRSV evolved, named the L1A variant. The phylogenetics, epidemic status, and pathogenicity of the LA variants were subsequently comprehensively evaluated. Based on the results of the ORF5 phylogenetic analysis, the L1A variants were classified as NADC34-like PPRSV. All the strains had the same discontinuous 131-aa deletion in the NSP2 region (similar to that in the NADC30). Recombination analysis revealed that the L1A variants were recombinant viruses that contained an NADC30-like PRRSV skeleton, a nonstructural protein-encoding gene region obtained in part from JXA1-like PRRSV and a ORF2-ORF6 gene region partly obtained from NADC34-like PRRSV and that exhibited similar recombination patterns. We successfully isolated the L1A variant TZJ2756 from PAMs and Marc-145 cells. In animal experiments, TZJ2756 exhibited moderate pathogenicity in piglets, causing obvious clinical symptoms, namely, persistent fever, significantlyreduced body weight, interstitial edema and severe interstitial pneumonia in the lungs, and prolonged high-load viremia. L1A variants have been detected in at least 12 provinces in China and share many similar epidemiological characteristics with the American L1C variant. This research will enhance our understanding of the prevalence of L1A variants and furnish valuable data for the ongoing monitoring of NADC34-like PRRSV in China.