Molecular Epidemiology and Genetic Evolution of Porcine Reproductive and Respiratory Syndrome Virus in Northern China During 2021-2023.

Porcine reproductive and respiratory syndrome virus (PRRSV), an important pathogen affecting the pig industry, is an RNA virus with high genetic diversity. In this study, 12,299 clinical samples were collected from northern China during 2021-2023 to investigate the molecular epidemiological characteristics and genetic evolution of PRRSV. All samples were screened using qRT-PCR and further analyzed through gene and whole-genome sequencing. The results showed that the positive rate of PRRSV in northern China was 18.42%, and positivity rates were relatively high in spring. The phylogenetic analysis of the gene indicated that the 174 gene sequences were classified as PRRSV-2, predominantly found in Lineage 1.8 (L1.8), Lineage 1.5 (L1.5), and Lineage 8 (L8). L1.8 and L1.5 showed considerable polymorphism at decoy and neutralizing epitopes. Mutations of specific amino acids were present in L1.8 and L1.5 at T- and B-cell epitopes. Moreover, the 27 whole-genome sequences were analyzed. As indicated, 24 of them were exposed to gene recombination, and L1.8 provided the backbone for recombination events. The predominant recombination modes were L1.8 + L8.7 + L1.5/L3, with L1.5 and L3.5 generally yielding GP2~GP6 structural proteins. Recombination hotspots were primarily located within the ranges of 780~2200 (Nsp1~Nsp2), 5400~6200 (Nsp3~Nsp4), 7800~9000 (Nsp9), and 12,200~14,800 (ORF2~ORF6). This study enriches the epidemiological data of PRRSV in northern China, thereby providing theoretical references for the prevention and control of PRRSV in northern China.