Background: Hepatitis-Hydropericardium syndrome (HHS), a significant disease in poultry, is caused by fowl adenoviruses (FAdV). While common in commercial flocks, HHS has not been previously documented in native chicken breeds in Iran. Case description: This case report describes HHS in a small backyard flock of native hens in Mashhad, Iran. The affected birds, three 6-month-old hens, exhibited lethargy for one day prior to death. Findings/treatment and outcome: Post-mortem examination revealed hydronephrosis, splenomegaly, hydropericardium, and hepatic necrosis. Histopathological examination showed significant lesions in the liver, heart, kidney, and spleen. The liver displayed congestion, hemorrhage, hepatocellular degeneration, necrosis, lymphocytic hepatitis, and large basophilic intranuclear inclusion bodies in the affected hepatocytes, confirmed by Lendrum’s phloxine-tartrazine method. Cardiac lesions included pericarditis, myocarditis, edema, and myofiber degeneration and necrosis. The spleen exhibited congestion and hemorrhage, while renal tissues showed tubular epithelial cell degeneration and necrosis with inflammation. PCR assay on the liver samples confirmed FAdV serotype 4. Conclusion: These findings show HHS and a FAdV serotype 4 etiology, highlighting the emerging threat of adenoviral diseases to noncommercial poultry settings in Iran.

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