Molecular characterization and evolutionary analysis of a duck astrovirus type 3 strain

Waterfowl astrovirus cause viral hepatitis, nephritis, and gout in ducklings and goslings, leading to growth retardation, reduced production performance, and poor feed conversion, and thereby pose a substantial threat to the waterfowl industry. In this study, we investigated the prevalence of waterfowl astrovirus by screening 293 samples from 30 batches collected from Shandong, Guangdong, Sichuan, Henan, and Liaoning provinces in China. Among the 27 samples obtained in Guangzhou, 12 tested positives for goose astrovirus (GAstV), yielding a positivity rate of 44.4 %, and all infected geese died at 6-10 days of age. Notably, two positive samples were collected from partridges, suggesting a potential cross-species transmission event. In addition, a novel astrovirus strain (TA422) was isolated from weak duck embryos, and full-genome sequencing revealed that TA422 shared 98.3 % nucleotide identity with the duck astrovirus type 3 (DAstV-3) CPH strain. To evaluate its pathogenicity, we established a SYBR Green Ⅰ-based qPCR assay and conducted animal challenge experiments in 9-day-old SPF duck embryos and 3-day-old ducklings. Infected embryos exhibited hemorrhaging, thickened allantoic membranes, urate deposition, growth retardation, and malformations. Hatched ducklings showed growth retardation and prolonged viral shedding, confirming vertical transmission of TA422. Moreover, infected ducklings also exhibited significant weight loss, persistent viral excretion, systemic inflammation responses and marked histopathological lesions in the liver and kidneys. In conclusion, this study characterized the epidemiology of waterfowl astrovirus in China, identified a novel DAstV-3 strain and provided experimental evidence for its vertical transmission. These findings could improve our understanding of waterfowl astrovirus evolution and offer a scientific basis for developing effective prevention and control strategies.