Fowl adenoviruses (FAdVs) in Iran between 2020 and 2022: the first comprehensive phylogenetic study.

Inclusion body hepatitis (IBH) outbreaks have been reported globally over the past two decades, predominantly affecting broiler flocks and resulting in significant economic losses due to increased mortality and diminished production performance. In Iran, fowl adenovirus (FAdV) infections have been circulating for several years, with recurrent reports of clinical cases suggesting IBH and hepatitis-hydropericardium syndrome (HHS) in commercial poultry operations. In response to these concerns, the present study was conducted to comprehensively characterize circulating FAdV strains in Iranian poultry farms over a 3-year period. A total of 200 pooled liver samples were collected from 200 broiler flocks that exhibited clinical signs consistent with IBH/HHS. Partial amplification and sequencing of the hexon gene were performed to detect and genotype the FAdV strains. The phylogenetic analysis assigned 66.32% of the detected strains to FAdV-D, 16.32% to FAdV-C, 11.22% to FAdV-E, and 6.12% to FAdV-B. Notably, this investigation provided the first genomic evidence of FAdV serotype 5 in Iran. Within the FAdV-C group, both serotypes 4 and 10 were identified. Additionally, serotype 6, closely related (98% nucleotide identity) to a Chinese reference strain, was reported for the first time in Iran. Given the high diversity of FAdV serotypes, continued vaccination of broiler breeders, using vaccines that cover the strains circulating in the country, is recommended. Monitoring broilers and broiler breeders remain essential for effective disease control and prevention.