Characterization of a Natural Recombinant Fowl Adenovirus of Serotypes 8a and 8b

Fowl adenoviruses ( FAdV ) infections have been reported in numerous countries worldwide. The hepatitis-hydropericardium syndrome ( HHS ) caused by FAdV-4 infection has inflicted enormous economic losses on the poultry industry in China, but it has been effectively controlled with the advancement of vaccine development. Currently, the main disease affecting poultry industry is chicken inclusion body hepatitis ( IBH ). FAdV strain XH2109, isolated from the liver of an IBH-affected broiler, was identified as a recombinant strain between FAdV-8a and -8b through whole-genome sequencing and recombination analysis. Additionally, this strain exhibited significant genetic divergence in the penton, hexon, fiber, hexon assembly protein 100K and GAM-1protein. Pathogenicity evaluation of XH2109 strain was conducted using 10-day-old specific pathogen-free ( SPF ) chickens. The results demonstrated that the XH2109 strain did not cause chicken mortality, but it significantly inhibited the growth of chickens and caused obvious lesions to the liver, spleen, bursa of Fabricius, and thymus. Antiserum against the XH2109 strain was prepared, and a neutralization test was performed using chicken embryos. It was found that this antiserum could effectively neutralize FAdV-8a and FAdV-8b. Collectively, these findings improve the current understanding of the genetic diversity of FAdV in China and provide valuable insights for the development of vaccines against IBH.