Evidence of vertical transmission of fowl adenovirus 8b in ducks.

Fowl adenovirus mainly causes hydropericardium hepatitis syndrome (HHS), inclusion body hepatitis (IBH) and gizzard erosion (GE), etc. In 2015, the first outbreak of HHS was reported in broiler chickens in central China, followed by an outbreak in waterfowl. The first outbreak of HHS in broiler flocks in central China in 2015, followed by outbreaks in waterfowl, has severely restricted the healthy development of the poultry industry. During the investigation, fowl adenovirus was detected in ducklings from a total of seven hatcheries in Shandong, Inner Mongolia and Jiangsu provinces. In addition, the DNA of fowl adenovirus was detected in breeding ducks and their progeny. To test the hypothesis that FAdV can be transmitted vertically, sixty 250-day-old Cherry Valley breeder ducks were divided equally into three groups for experimental infection. FAdV-8b SDLY isolate (duck/Shandong/SDLY/2021, SDLY) preserved in our laboratory was injected intramuscularly into group A and inoculated orally into group B. FAdV-8b DNA was detected in the yolk membranes, embryos and allantoic fluid of duck embryos in the FAdV-infected group after inoculation. In addition, the FAdV-8b hexon gene isolated from yolk membranes, embryos, allantoic fluid and duck eggs was close to 100% nucleotide homology to the FAdV-8b hexon gene isolated from laying duck ovaries, indicating that fowl adenovirus can be transmitted vertically in ducks. These findings provide evidence for the possible vertical transmission of fowl adenovirus from breeder ducks to ducklings.