Canine adenovirus type 1 (CAdV-1) in free-ranging European brown bear (Ursus arctos arctos ): A threat for Cantabrian population?

Abstract

Canine adenovirus type 1 (CAdV-1) is responsible for infectious canine hepatitis. The disease has been described in captive American black bear (Ursus americanus) and European brown bear (Ursus arctos arctos), with just one recently reported case in a cub of a free-ranging brown bear (Ursus arctos horribilis) from Alaska. The aim of this work is to summarize findings related to presence and associated mortality of CAdV-1 in 21 free-ranging Cantabrian brown bears (Ursus arctos arctos) submitted to necropsy in Asturias and Castilla y León (northwestern Spain) from 1998 to 2018. On the basis of the anatomopathological findings and laboratory results three free-ranging brown bears died due to infectious canine hepatitis, which is to our knowledge the first description of death due to this disease in free-ranging bears in Europe. Gross lesions consisted of petechial haemorrhages and congestion in different internal organs, haemorrhagic fluid in internal cavities, friable and yellowish liver and thickening of gall bladder. Microscopic lesions were observed mainly in liver, kidney and brain and consisted of multifocal necrosis of cells with presence of basophilic intranuclear inclusions. Immunohistochemical (IHC) and real-time polymerase chain reaction (qPCR) techniques were used to assess the presence of CAdV-1 in paraffin-embedded liver samples. Viral antigens were detected by IHC labelling within hepatocytes and Küppfer cells in the three animals. The presence of viral DNA was confirmed by qPCR in one of them. In order to evaluate the circulation of CAdV-1 in brown bears, a retrospective study was performed using both IHC and qPCR techniques in 11 and 12 additional brown bears, respectively. An extra brown bear was found positive by IHC. This study shows that CAdV-1 surveillance of brown bears and sympatric carnivores should be considered as major concern for the monitoring the population evolution throughout time in this endangered species.

Mortality in free-ranging Eurasian brown bears (Ursus arctos arctos) in Spain '1998-2018'

“…Another possibility might be a high degree of circulation of the pathogens both in the environment and sympatric species (i.e. CAdV-1 carriers such as wolves or not sanitarily controlled dogs in rural areas) [6].…”

“…Gross lesions in the three bears (bears number 11, 14 and 20) with infectious canine hepatitis caused by CAdV-1 was previously described [6] and consisted of congestion and hemorrhages in several organs; hemorrhagic uid in thoracic and abdominal cavities; friable and yellow-tinged liver; hepatomegaly; thickening of the gall bladder due to edema [6]. Microscopically the main pathological ndings appeared in liver and gall bladder.…”

“…After the detection of one dead animal and the exhaustive examination of the area in the eld where the bear was found, a complete post mortem examination of each carcass was conducted at the University of León or Servicio Regional de Investigación y Desarrollo Agroalimentario (SERIDA, Asturias). Tissue samples were taken for evaluation using standard methods in microbiology [5], molecular techniques [6], virology [6], parasitology (coprologic study), toxicology and histopathology [5][6][7].…”

“…The pathological ndings on six animals revealed secondary bacterial infection followed by primary traumatic event caused either by human activities or natural causes. Three causes of death (Clostridium sordellii infection in one bear, infectious canine hepatitis caused by canine adenovirus type 1 (CAdV-1) in three bears and cholangiocarcinoma in one bear) had been already described in previous papers by our group [5][6][7].…”

“…Additionally, non-purulent encephalitis was observed. CAdV-1 was con rmed by quantitative polymerase chain reaction (qPCR) and immunohistochemistry [6].…”