Pathogenicity of FAdV-D serotype 2 in broiler and layer chicks

Eighty, 1-day-old (DO) broiler chicks and 80 1-DO male layer chicks were experimentally infected with two isolates of fowl adenovirus D (FAdV-D) serotype 2 isolated from broiler chickens suffering inclusion body hepatitis (IBH) (accession numbers ON603311 and ON603320). Clinical observation was performed up to 28-DO, and samples from the liver, pancreas, kidneys, spleen, thymus, and bursa of Fabricius were collected for histopathological examination. Furthermore, FAdV-D viral shedding was tested up to 21DO. Serological response to IBH (FAdV-D) through enzyme-linked immunosorbent assay (ELISA) and blood biochemical analysis, as well as polymerase chain reaction (PCR) testing for some innate immune response parameters (interleukins and cytokines) to IBH were applied. Also, immune response of chicks to avian influenza and Newcastle disease vaccines was evaluated using the haemagglutination inhibition (HI) test. No mortality was observed following experimental infection of either broiler or layer chicks with FAdV-D serotype 2 isolates, despite the clearly evidenced histopathological damage in the liver, pancreas, kidneys, spleen, thymus, and bursa of Fabricius. Viral shedding extended to 21DO. Neither isolate could induce serological response, but both elevated the interleukins and cytokines. In conclusion, broilers were more susceptible to IBH-FAdV infection than layer chicks. FAdV-D serotype 2, which causes IBH, had an immunosuppressive effect on chickens.