Molecular detection and pathological evaluation of canine adenovirus 1 in Indian bear species.

In this study, we investigated infectious canine hepatitis (ICH), caused by canine adenovirus 1 (CAdV-1), in 125 bear carcasses submitted for examination. CAdV-1 is known to cause severe disease in domestic dogs and in wild canids and bears. Using molecular and/or histopathological methods, CAdV-1 infection was confirmed in 12 cases: 11 in sloth bears (Melursus ursinus) and one in an Asiatic black bear (Ursus thibetanus). Affected captive bears exhibited acute onset of high fever, jaundice, bloody vomitus, and foul-smelling diarrhoea, followed by death. Necropsy revealed widespread congestion and petechial-to-ecchymotic haemorrhages across multiple visceral organs. Histopathological examination showed marked vascular changes, including engorged blood vessels, oedema, and haemorrhages. Intranuclear basophilic inclusion bodies were observed in endothelial cells, hepatocytes, and Kupffer cells. Immunohistochemistry confirmed the presence of CAdV-1 antigen in endothelial cells of various organs, as well as in hepatocytes and Kupffer cells in the liver. Molecular analysis identified a strain closely related to CAdV-1 isolates previously reported in domestic dogs and other carnivores in various parts of the world. The virus was successfully isolated in MDCK cells from sloth bear samples. Among 99 live sloth bears tested, 41.4% were seropositive for CAdV-1 antibodies. Our findings confirm the susceptibility of these bear species to CAdV-1 and highlight the need for ongoing surveillance, as well as the importance of vaccination in captive bear populations to prevent the spread of this disease.