Genetic and Pathogenic Characteristics of Novel PRRSV-1 Strain CH-JX-2504 and CH-SDTA-2506 in China.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a leading cause of severe economic losses in the worldwide swine industry. In recent years, the geographic distribution of PRRSV-1 has been expanding, further complicating epidemic prevention and control. In 2025, two PRRSV-1 strains were successfully isolated from lung tissue samples of deceased pigs in Jiangxi and Shandong Provinces of China, named CH-JX-2504 and CH-SDTA-2506, respectively. Viral isolation was performed using primary porcine alveolar macrophages, and whole-genome sequencing was performed through metagenomic analysis. Subsequent phylogenetic analysis indicated that strain CH-JX-2504 belonged to the new subgroup 3, while CH-SDTA-2506 clustered within the BJEU06-1-like subgroup. Amino acid sequence analysis showed that CH-JX-2504 exhibits identical deletion patterns in the Nsp2, GP3, and GP4 proteins with the PRRSV-1 reference strain 180900-5. In contrast, distinct variations in these three proteins were identified in CH-SDTA-2506 compared with other representative PRRSV-1 strains, suggesting the emergence of a novel deletion pattern. In vivo challenge experiments showed that both CH-JX-2504 and CH-SDTA-2506 could induce typical clinical symptoms in piglets, including fever, retarded weight gain, and pathological lesions, including interstitial pneumonia with lymphocyte infiltration, obvious damage to intestinal villi, and disruption of the intestinal microbiota structure. Notably, one piglet in the CH-JX-2504 group died at 10 days postinfection (dpi), indicating that CH-JX-2504 exhibits higher pathogenicity than CH-SDTA-2506. Therefore, strengthened surveillance of PRRSV-1 in China is essential to prevent its further spread.