Fowl adenoviruses recently became a hot topic for most Egyptian researchers and investigators, where the Egyptian poultry industry suffered from several outbreaks of fowl adenovirus (FAV) attacks in commercial broiler flocks. As vertical transmission from the parent flock represents the most common infection, the present study aimed to investigate the molecular characterization of FAV species isolated from commercial broiler breeder flocks in northern Egypt from 2021 to 2023. Organ samples and swabs from 10 breeder flocks have been examined in real-time. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) revealed positivity for fowl adenovirus, with variable PCR cycle threshold (CT) values ranging from 10 to 36. The loop1 (L1 regions) on the hexon gene of the ten positive samples have been amplified by conventional PCR, which resulted in only three positive samples at molecular size 800 bp, and only one representative PCR product has been sequenced for the L1 region. The genetic characterization revealed the first record for the existence of serotype 7 of FAV-species E in Egypt. The sequenced sample is similar to strain 12-10101 with an identity of 97%.
Histopathological examination revealed inclusion body hepatitis associated with abundant apoptosis, hydropericardium , myocarditis, pancreatic acinar cell necrosis, glomerulonephritis, and acute tubular necrosis. FAV antigen was demonstrated in examined tissues using avidin-biotin-peroxidase. Inaddition, cleaved caspase-3 immunohistochemical staining revealed strong positive immune reactivity in the liver, pancreas, and kidneys.  Proliferating cell nuclear antigen (PCNA) immune staining revealed positive immune reactivity in the regenerating renal tubules.