Epidemiological and molecular characteristics of porcine reproductive and respiratory syndrome virus in China from 2015 to 2024

The Chinese swine sector continue to face great challenges from porcine reproductive and respiratory syndrome virus (PRRSV). Analysisof 411,392 samples collected from 2015 to 2024 revealed a clear V-shaped trend in PRRSV positivity. The rate bottomed out at 3.63% in 2021 and then increased back to 7.85% by 2024. Phylogenetic analysis of 2,294 ORF5 sequences revealed a conspicuous lineage replacement event, in which sublineage 8.7 was gradually supplanted by sublineages 1.8 (NADC30-like) and 1.5 (NADC34-like). Notably, sublineage 1.5 became the predominant strain by 2024, accounting for 55.31% of the sequences. Whole genome sequencing of 48 isolates revealed incongruent phylogenetic relationships between the non-structural protein 2 (NSP2) and ORF5/whole-genome markers. We identified sublineage-specific deletions within NSP2, point mutations in GP5, and multiple recombination events. These recombination events occurred between the NADC30-like strains and either the VR-2332 or the JXA1 strains. Consequently, sublineages 1.8 and 1.5 have replaced sublineage 8.7 to be the dominant PRRSV strains in China, with intersublineage recombination driving the genetic complexity of PRRSV evolution.