Isolation and characterization of a novel S-gene mutation porcine deltacoronavirus with high pathogenicity from diarrhea piglet in Zhejiang Province, China, 2022.

Porcine deltacoronavirus (PDCoV) is a coronavirus that causes diarrhea in suckling piglets and has the potential for cross-species transmission. Monitoring PDCoV evolution and identifying potential vaccine candidates are crucial due to its high mutation rates in pig populations. In this study, a Chinese PDCoV strain named ZD2022 was successfully isolated from diarrhea piglets in Zhejiang province, followed by genetic evolutionary analysis, assessment of S proteins' biological functions, in vitro cellular adaptation analysis and pathogenicity evaluation. Phylogenetic analyses placed the PDCoV ZD2022 strain within the Southeast Asia Lineage. Sequence analysis revealed 23 mutations in the S protein of ZD2022 compared to most of other Chinese PDCoV strains, including 8 unique mutations (T529I, L579F, Q614H, V709G, S959L, P1010S, V1016F, A1068V). In addition, bioinformatic predictions indicated these mutations impact the hydrophilicity/hydrophobicity, antigenic epitopes and N-glycosylation sites of the ZD2022 S protein. The virus growth curve of ZD2022 showed good cellular adaptation, with peak viral titers of 8.92 ± 0.31 Log TCID/mL in ST cells. Furthermore, ZD2022 exhibited high virulence in suckling piglets, causing severe diarrhea in piglets at 60 h post-inoculation (hpi) and a mortality rate of 40 % (2/5) within 96 hpi. In summary, our findings indicate that the Chinese PDCoV strains continue to mutate, and the novel S gene mutation in strain ZD2022 offers strong cellular adaptation and high pathogenicity, making it a potential candidate strain for vaccine development.