Characterization of a duck circovirus propagated in duck embryos: from genome to pathogenesis in SPF ducks.

Duck circovirus (DuCV) is a major pathogen in duck farming that causes immunosuppression and increases the susceptibility to secondary infections. This study focused on a Chinese DuCV strain, designated SDDC, which was isolated and characterized from Cherry Valley ducks in Shandong Province in 2022. The SDDC strain was successfully propagated in specific-pathogen-free (SPF) duck embryos and confirmed by transmission electron microscopy. Genomic analysis identified a complete genome of 1994 bp, with a critical amino acid mutation (I to T) at the 160th position in the Cap protein, potentially influencing viral tropism. Pathogenicity studies in 2-day-old SPF ducks revealed a multi-organ infection, with the spleen as the primary target, exhibiting the highest viral load and significant histopathological alterations. Analysis of multi-organ viral dynamics indicated a detectable viral presence across target organs as early as 3 dpi, followed by a progressive decline in viral load until day 7. A pronounced replication peak was observed on day 14, after which a gradual viral clearance occurred. This study provides critical insights into the genomics, pathogenicity, and tropism of DuCV, establishing a foundation for elucidating its infection mechanisms, and developing targeted control strategies to protect duck farming.