Pathogenicity and Genomic Features of a DAdV-3 Strain Causing Severe Hepatitis in Muscovy Ducklings

Over the past decade, there has been an increase in reports of duck adenovirus type 3 (DAdV-3) infections in Muscovy ducks across various provinces in China, with mortality rates reaching as high as 43%. The rising incidence of this disease has led to significant economic losses for the waterfowl farming industry in China. In this study, a DAdV-3 strain was isolated from a Muscovy duck farm in Fujian province, which we designated as the FJNP-2021 strain, and further explored its pathogenicity and genetic characteristics. Pathogenicity analysis demonstrated that this FJNP-2021 strain induces characteristic pathological changes in Muscovy ducklings, exhibiting a broad tissue tropism, with the liver exhibiting the most severe lesions. The ultrastructural analysis revealed significant accumulation of lipid droplets and structurally disordered endoplasmic reticulum (ER) surrounding mitochondria in the hepatocytes of Muscovy ducklings postinfection. Moreover, in vivo DAdV-3 infection significantly downregulated ferroptosis suppressive genes (SLC7A11, GPX4, and FTH1) while upregulating proferroptotic genes TP53 and CHAC1. Our study provides dual ultrastructural morphology and molecular evidence that DAdV-3-induced hepatic lipid metabolism disorder triggers ferroptosis, thereby exacerbating hepatocyte injury. Phylogenetic analysis revealed that the complete genome sequence of the FJNP-2021 strain exhibited 92.3% identity with the representative strain GR from France, which was clustered in a different evolutionary lineage. Furthermore, the FJNP-2021 strain was grouped within the same lineage as domestic DAdV-3 strains, consistent with the genetic characteristics of the predominant epidemic strains of DAdV-3 in China. Notably, the Fiber1 genes of the Chinese DAdV-3 isolates formed two distinct subclades, and the Fiber1 gene of the FJNP-2021 strain clustered within the major subclade. In conclusion, this study analyzed the pathogenicity and genetic characteristics of all available DAdV-3 strains, enriching our understanding of the genomic diversity of Chinese isolates from 2014 to 2024 and providing a basis for further studies on DAdV-3 evolution and pathogenesis.