Genetic diversity and pathogenicity of novel recombinant strains of PRRSV lineages 1.5, lineages 1.8 and lineages 8 in South China.

Porcine reproductive and respiratory syndrome virus (PRRSV), particularly genotype 2 (PRRSV-2), inflicts substantial economic losses on the global swine industry. In China, Lineage 1 of PRRSV-2 has been the dominant epidemic strain since 2016 and is characterized by frequent recombination. This study investigated the molecular epidemiology of PRRSV in Southern China from 2022 to 2024. Among 1, 139 clinical samples from Guangdong, Guangxi, and Hainan provinces, the overall PRRSV positivity rate was 40.6% (463/1, 139). NADC30-like (Lineage 1.8, 49.9%) and NADC34-like (Lineage 1.5, 31.1%) strains were identified as the most prevalent. A novel recombinant strain, designated DJW, was successfully isolated using porcine alveolar macrophages. Whole-genome and GP5 phylogenetic analyses revealed DJW as a triple-recombinant mosaic virus. It possesses a NADC30-like backbone but has undergone recombination with HP PRRSV-like strains in the NSP3-NSP9 region and with NADC34-like strains in the ORF2-ORF6 region. Pathogenicity assessment in piglets demonstrated that DJW infection causes severe clinical signs, including persistent fever, significant viremia, robust viral shedding, extensive lung consolidation, and one death observed in the challenge group (1/5). Our findings highlight the ongoing evolution of PRRSV through recombination.