The replication efficacy of NADC34-like porcine reproductive and respiratory syndrome virus 2 is not directly associated with the pathogenicity

Abstract

NADC34-like porcine reproductive and respiratory syndrome virus 2 (NADC34-like PRRSV-2) is currently a major prevalent strain in Chinese swine industry. Within which, recombination events are frequently detected. Previous studies have shown that the pathogenicity of NADC34-like PRRSV-2 isolates is highly variable. However, the characteristics between NADC34-like PRRSV-2 recombinant and non-recombinant isolates are rarely compared. In this study, two PRRSV-2 strains (BJ1805–2 and SDLY23–1742) were isolated from samples collected at 2018 and 2023 in China. ORF5-based phylogenetic analysis supported that both isolates are clustered with ORF5 RFLP 1–7–4 (NADC34-like) strains. However, genome-based phylogenetic tree showed that BJ1805–2 is still grouped with NADC34-like isolates but SDLY23–1742 is clustered with NADC30-like viruses. Furthermore, fragment comparisons and recombination detections also supported that SDLY23–1742 was recombined from NADC30-like, NADC34-like, and JXA1-like isolates while no recombination event was detected in BJ1805–2. Noticeably, BJ1805–2 had higher replication efficacy than SDLY23–1742 both in PAMs and in piglets. However, SDLY23–1742 caused longer high fever period and more severe histopathological lung lesions than BJ1805–2, indicating that SDLY23–1742 has higher pathogenicity than BJ1805–2. Overall, this study provides the first evidence that the pathogenicity of NADC34-like PRRSV-2 is not directly correlated with viral replication efficacy.