Pathogenicity by parenteral injection of fowl adenovirus isolated from gizzard erosion and resistance to reinfection in adenoviral gizzard erosion in chickens

The pathogenicity of a serotype-1 fowl adenovirus (FAV-99ZH), which causes adenoviral gizzard erosion by oral inoculation in chickens, was investigated in specific pathogen-free white leghorn chickens. In trial 1, 14 chickens were inoculated intravenously with the virus at 21 days of age and euthanatized for necropsy within 1-14 days of inoculation. Gizzard erosion was grossly observed from day 7 postinoculation (PI), and histologically, FAV-99ZH antigen-positive, basophilic intranuclear inclusion bodies were seen in the gizzard lesions from day 7 to 11 PI. Necrotizing pancreatitis, and cholecystitis and cholangitis associated with the inclusions were observed from day 3 to 14 PI (pancreatitis) and from day 5 to 9 PI (cholecystitis and cholangitis), respectively. The inclusions were also observed in the epithelial cells of the cecal tonsils from day 3 to 5 PI. The virus was recovered from samples of the lesions. It was revealed that FAV-99ZH causes not only gizzard erosion but also pancreatitis, cholecystitis, and cholangitis by intravenous inoculation in chickens. In trial 2, 10 chickens were inoculated orally with the virus twice, at 13 and 36 days of age, and euthanatized for necropsy within 4-17 days after reinfection. Macroscopically, focal gizzard lesions were observed; however, neither necrosis nor inclusions were observed by microscopy. Moreover, FAV was not recovered from the gizzard or rectum of any of the chickens at necropsy. This suggests that the gizzard lesions occurred as a result of the primary infection, and that the chickens were able to resist reinfection.