Impact of duck astrovirus on susceptibility to infection across duck ages

An outbreak of duck astrovirus (DAstV) has occurred in duck farming regions of China, causing substantial economic setbacks in the duck industry. This investigation aimed to examine the variations in DAstV pathogenicity among ducks at different age intervals. Infections were induced in ducks at distinct age groups (1, 7, 14, 21, and 28 d) utilizing the DAstv-1-GDB-2022 strain. The results indicate increased pathogenicity of the DAstv-1-GDB-2022 strain in ducklings aged 21 to 28 d, manifesting as liver and kidney enlargement, severe bleeding, and potential fatalities. Conversely, ducklings aged 1 and 14 d displayed milder symptoms postinfection. Notably, viral shedding continued in ducks of diverse age groups even 21 d postinfection (Dpi). Moreover, DAstV replicates in various tissues, predominantly affecting the liver. Immunohistochemical tests using rabbit anti-DAstV antibodies revealed robust positive signals in both the liver and kidneys, which correlated with the clinical symptom severity observed through macroscopic and microscopic examinations. Serum biochemical assays and indirect ELISA demonstrated a consistent response to DAstV infection across different age groups, with older ducklings exhibiting increased sensitivity. In conclusion, this study successfully replicated clinical symptoms similar to those of natural DAstV infection using the DAstv-1-GDB-2022 strain. Importantly, we systematically delineated the differences in susceptibility to DAstV among ducks at various ages, laying the foundation for further research into the pathogenic mechanisms of DAstV and potential vaccine development.

Isolation and detection of duck astrovirus CPH: implications for epidemiology and pathogenicity

The transmission routes of duck astrovirus CPH (DAstV/CPH) and its pathogenicity in duck embryos were investigated. Using a reverse transcription-polymerase chain reaction (RT-PCR) developed in this study, DAstV/CPH was detected in 23/50 fresh droppings of breeder ducks, 39/65 breeding eggs, 26/31 dead embryos, and 6/10 newly hatched ducklings, which were taken from a Pekin duck farm where DAstV/CPH had previously been identified. This finding, and the detection of DAstV/CPH in 36/130 dead-in-shell duck embryo samples collected from different hatcheries located in six provinces, suggests that the virus may be horizontally and vertically transmitted and associated with hatchability problems. Inoculation and repeated passages in embryonating duck eggs resulted in isolation of DAstV/CPH. The virus caused severe chorioallantoic membrane lesions as well as growth retardation and embryo mortality, indicating that DAstV/CPH is pathogenic for duck embryos. The effect of DAstV/CPH on hatching was confirmed by an embryo infection experiment in which 8/10 9-day-old duck embryos inoculated with the third passage of DAstV/CPH were unable to hatch, with most embryos succumbing in the final stage of incubation. The use of RT-PCR on the hatched ducklings provided evidence that the embryos could develop into infected ducklings.