Molecular and histopathological characterization of fowl adenovirus serotype 4 in broiler chickens in Kashan, Iran: implications for disease control and prevention in the poultry industry.

Fowl adenovirus (FAdV) is a DNA virus causing significant diseases, like inclusion body hepatitis, hydropericardium-hepatitis syndrome (HHS), and gizzard erosion. These diseases lead to severe economic losses in the poultry industry. Recent increases in HHS outbreaks in Iran, particularly among broilers, prompted this study to analyze FAdV isolates in Kashan, Iran. In December 2021, a high-mortality HHS outbreak in a Kashan broiler flock led to liver and heart samples being sent for analysis. Histopathological investigations revealed mononuclear hepatitis and intra-nuclear viral inclusion bodies in hepatocytes. Polymerase chain reaction and phylogenetic analyses confirmed the presence of FAdV-4 (accession number: PP856395), showing 99.99% identity with strains from Japan, the United Arab Emirates, Pakistan, and the United States. These findings highlight the genetic similarity and potential common origin of FAdV-4 strains. This study emphasizes the need for heightened biosecurity measures and effective vaccination strategies to mitigate the spread of FAdV-4. The confirmed presence of FAdV-4 in central Iran poses a significant threat to the poultry industry, necessitating prompt action to prevent substantial economic losses.