A strain of high cell-adapted porcine deltacoronavirus: Isolation, genetic evolution, and pathogenicity analysis.

In 2024, an outbreak of piglet diarrhea occurred in Guangxi Zhuang Autonomous Region, China. RT-PCR assay of clinical samples confirmed that porcine deltacoronavirus (PDCoV) was the primary pathogen. In this study, the PDCoV GX/2024 strain was successfully isolated in PK-15 cells with optimized trypsin treatment conditions. The cytopathic effect (CPE) of this strain gradually intensified during serial passages. After plaque purification, the strain achieved stable proliferation with high titer, reaching a peak titer of 107·2 TCID50/mL, which indicated its potential as an inactivated vaccine candidate. Phylogenetic analysis demonstrated that the strain belonged to the Chinese lineage, with nucleotide similarity ranging from 97.89% to 99.76% compared with other domestic and international strains. Analysis of the Spike protein (S protein) revealed that the strain harbored critical amino acid substitutions in the S1 domain and the S1/S2 cleavage site, which led to conformational changes in the protein surface and might be associated with viral infection efficiency. Animal experiments verified that PDCoV GX/2024 exhibited strong pathogenicity in newborn piglets. Diarrhea, vomiting and other symptoms appeared within 24 h post-infection. The virus mainly colonized the epithelial cells at the tip of intestinal villi and caused severe pathological damage. This study provides important theoretical basis for the genetic evolution, pathogenic mechanism and transmission potential of PDCoV, and offers reference value for disease prevention and control as well as vaccine development.