Hydropericardium syndrome (HPS) has caused significant financial losses to the Iranian poultry industry in the past few years. Thirty-two broiler chickens with gross lesions of HPS were inspected histologically and immunohistochemically. Sampling was performed in Sabzevar, and dead and sick birds from random farms were subjected to necropsy examinations. Only four broiler chickens had no hydropericardium, and the other gross findings were similar for birds. Basophilic and eosinophilic intranuclear inclusions, hemorrhages, and necrosis in different organs were the primary characteristic histologic lesions. Lymphoid depletion, goblet cell hyperplasia, and necrotizing enteritis were some of the findings reported in previous research. Low macrophage infiltration rate and brain lesions were other discoveries in hematoxylin and eosin (H&E) examination. Feulgen reaction and CD68 immunohistochemical staining were used for a comprehensive investigation, and these techniques revealed improved histopathologic details. Feulgen staining confirmed brain lesions and some other changes in different organs. Eventually, the CD68 method revealed low macrophage presence in most organs. This study suggests that HPS may cause brain damage, and the susceptibility of the Arian breed to the adenovirus needs further investigation.

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