Epidemiological analysis based on ORF5 of porcine reproductive and respiratory syndrome virus in China in 2019–2024

Introduction: Porcine reproductive and respiratory syndrome virus (PRRSV) was first reported in pigs in China in 1996. At present, multiple PRRSV lineages and sub-lineages are circulating in Chinese swine herds. Methods: In this study, PRRSV ORF5 sequences collected from 2019 to 2024 were analyzed to investigate their spatiotemporal distribution, molecular evolution, and major amino acid mutations. Results: A total of 674 sequences were obtained from 25 provinces between 2019 and 2024, and their geographical distribution was generally consistent with the major pig-producing regions in China. Phylogenetic analysis revealed that these PRRSV ORF5 sequences mainly belonged to lineage 1 (L1A, L1C), L3, L5 (L5A), and L8 (L8E). From 2019 to 2024, the proportion of L1C initially increased, followed by a decrease and a subsequent rebound, while L1C remained the predominant sub lineage. The proportion of L1A showed a relative increase, whereas L3 was detected at very low levels. Meanwhile, L5A and L8E exhibited a downward trend. Amino acid mutations were observed in the signal peptide, neutralizing epitopes, and T-cell epitopes among different sub-lineages. Some mutations were variable, while others were sub-lineage-specific. Notably, partial L1C strains exhibited an amino acid deletion at position 34, which may affect the viral immune evasion mechanisms. Nucleotide and amino acid identities initially decreased and then increased, with the most pronounced divergence observed in 2021. Discussion: Continuous monitoring of the molecular epidemiology of PRRSV is essential and will provide a scientific basis for the further prevention and control of PRRSV in China.