We performed gross and histological examinations of the livers of sika deer (Cervus nippon yesoensis) in Hokkaido, Japan. Out of 1,381 deer slaughtered for venison production, thickening and dilation of the large intrahepatic bile ducts and Fasciola flukes in the duct lumens were detected in 621 deer (45.0%). Furthermore, 107 non-bile lesions (75 intrahepatic and 32 capsular lesions) were detected during gross examinations. Histologically, the bile duct lesions included chronic proliferative cholangitis, papillary hyperplasia, goblet cell and pyloric gland metaplasia, and periductal fibrosis. Many of the intrahepatic non-bile duct lesions (53/75, 71%) were considered to be Fasciola fluke migration-associated lesions, including two lesion types: necrosis, hemorrhage, and eosinophilic granuloma formation (29 lesions), and lymphoid tissue formation (24 lesions). Lymphoid tissue formation was considered to result from the persistent immune responses against dead Fasciola flukes. An epidermoid liver cyst was found incidentally, which has not been reported in the veterinary literature. In summary, this study demonstrated the predominance of fascioliasis-associated lesions in sika deer livers. The gross and histological lesions caused by Fasciola flukes in sika deer were similar to fascioliasis in other animals. Moreover, we described lymphoid tissue formation as a fascioliasis-associated lesion for the first time. The fact that bile duct lesions (45.0%) had a markedly higher prevalence than fascioliasis-associated parenchymal lesions (53/1,381, 3.8%) indicated that sika deer are a permissive host for fascioliasis. Our results provide information that will aid pathological examinations of sika deer.

A slaughtered 2-year-old female sika deer (Cervus nippon yesoensis) had diffusely distributed multinodular lesions on the serosal surface of the peritoneal cavity and several nodules in the pleural cavity. Histologically, they were composed of proliferating spindle-shaped neoplastic cells, arranged in a fascicular fashion. The cells in the invasive foci transitioned from a sarcomatoid to an epithelioid appearance. Immunohistochemically, both the spindle-shaped and epithelioid cells were at least focally positive for pancytokeratin, vimentin, calretinin, α-SMA, and desmin. From these findings, the deer was diagnosed with peritoneal sarcomatoid mesothelioma with metastasis to the pleural cavity. To our knowledge, this is the first reported case of peritoneal mesothelioma in a cervid species and the first case of mesothelioma in a sika deer.

A white nodule was detected in the liver of a wild female sika deer. The nodule was histologically diagnosed as squamous cell carcinoma (SCC), and it transitioned into a hyperplastic and chronically inflamed intrahepatic bile duct showing Fasciola infection. Therefore, the tumor was demonstrated to have originated from the biliary epithelium of the intrahepatic bile duct. Hyperplastic and chronic inflammatory changes of the biliary epithelium might have contributed the carcinogenesis of the present case, as proposed in human primary intrahepatic SCC cases. To the best of our knowledge, this is the first reported case of primary intrahepatic SCC in an animal.