Molecular characterization and pathogenicity of a novel Chinese porcine deltacoronavirus strain CH/HLJ/20 isolated from diarrheic piglets.

Porcine deltacoronavirus (PDCoV) is an emerging enteric coronavirus that causes acute diarrhea and high mortality in neonatal piglets. In this study, we isolated and characterized a novel PDCoV strain, CH/HLJ/20, from diarrheic piglets in Northeast China. Full-length genome sequencing and phylogenetic analysis revealed that CH/HLJ/20 belongs to the Chinese lineage but harbors distinct recombination signals within the S gene, with Korea/DH1/2017 and CHN/Tianjin/2016 identified as putative parental strains. Comparative analysis identified two unique amino acid substitutions (Q10H and N98K) within the receptor-binding domain (RBD) of the spike protein. Structural modeling and molecular docking revealed that the CH/HLJ/20 RBD retains binding compatibility with aminopeptidase N (APN) receptors from multiple species, including pig, human, dog, cat, and chicken, indicating broad host receptor adaptability. Docking simulations using sequence-reverted mutants suggested that these substitutions may slightly attenuate receptor-binding affinity, potentially influencing cross-species transmission. Notably, the N98K residue has been identified as a critical site involved in both APN binding and neutralizing epitopes, therefore, its mutation may influence receptor engagement and antigenic properties. In vivo virus infection experiments demonstrated that CH/HLJ/20 caused rapid disease onset and 100% mortality in neonatal piglets, with severe villous atrophy and high intestinal viral loads. These findings highlight the evolving genomic diversity, pathogenicity, and zoonotic potential of PDCoV, underscoring the critical importance of continuous viral surveillance, timely isolation and functional characterization of emerging strains, and enhanced understanding of cross-species transmission mechanisms to inform effective disease control and prevention strategies.