Epidemiology and Pathogenicity Analysis Based on Partial Recombinant PRRSV Strains in China

Currently, multiple recombinant variants of porcine reproductive and respiratory syndrome virus (PRRSV) are circulating in China. These variants exhibit differences in pathogenicity. To comprehensively understand the current status of the virus and its recombination patterns, a total of 677 PRRSV strains were used for evolutionary analysis, of which 673 strains were isolated from mainland China. The results indicated that current PRRSV strains in circulation in China are highly complex, with NADC30-like strains having replaced highly pathogenic strain of PRRSV (HP-PRRSV) strains as the dominant strains. An analysis of the patterns and hotspots of PRRSV-2 recombinant strains from 2019 to 2023 revealed two main types: the strains with NADC30 as the primary parent were observed to have recombination hotspots concentrated in the Nsp1, Nsp4 to Nsp9, and ORF2 to ORF6 regions, while recombination frequencies were found to be lower in the Nsp2, Nsp10, and Nsp11 regions. In contrast, the other type of recombinant strain, primarily derived from HP-PRRSV, exhibited recombination hotspots concentrated in the Nsp2 and ORF2 to ORF6 regions, while the recombination frequency in the Nsp8 and Nsp9 regions was relatively low. Further, a comprehensive analysis of the phylogenetic and recombination patterns of four PRRSV strains (ZJ-2021-1, JS-2020-1, GZ-2022-1, and SH-2020-2) indicated variations in genotyping precision among Nsp2, ORF5, and the entire genome. As demonstrated by the results of the animal experiments, there were differences in pathogenicity between ZJ-2021-1 and JS-2020-1. The pathogenicity of the recombinant strain exhibited similar characteristics to its parental skeleton. Our results provided reference data for exploring epidemiological characteristics and pathogenicity of recombinant PRRSV strains.