DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03201

Prominent hepatic ductular reaction induced by Oschmarinella macrorchis in a Hubbs’ beaked whale Mesoplodon carlhubbsi, with biological notes

Shotaro Nakagun*, Akira Shiozaki, Mari Ochiai, Ayaka Matsuda, Yuko Tajima, Takashi Matsuishi, Kenichi Watanabe, Noriyuki Horiuchi, Yoshiyasu Kobayashi

*Email: snakagun@gmail.com

ABSTRACT: Beaked whales are among the least known group of cetaceans, and information regarding their pathology and parasitology are especially scarce. We describe a case of significant parasitism by a trematode found in the liver of an adult male Hubbs’ beaked whale Mesoplodon carlhubbsi that stranded in Hokkaido, Japan. Post-mortem examinations revealed a localised area of discolouration restricted to the hilar region of the left hepatic lobe, where spindle-shaped trematodes occupied the dilated and hypertrophic bile ducts. Histologically, the intrahepatic bile ducts were characterised by adenomatous hyperplasia with goblet cell metaplasia of the biliary epithelium. Findings in the adjacent hepatic parenchyma included pseudocarcinomatous ductular reactions obliterating hepatocytes, a histomorphology not previously reported in marine mammals. Morphological identification of the trematode corresponded to Oschmarinella macrorchis, which has only been reported once in a Stejneger’s beaked whale M. stejnegeri. PCR amplification and sequencing analyses of the parasite’s mtDNA ND3, 18S and 28S rRNA regions generated novel gene sequences. Environmental contaminant levels were measured to explore its potential relationship with the parasitism but there was no conclusive association. A high level of polychlorinated biphenyl (30000 ng g–1 lipid weight) was detected in the blubber of this individual, when compared to those of 3 other male Hubbs’ beaked whales stranded in Japan. Stomach contents were also analysed indicating the presence of various squid species and unidentified fish. Our results contribute to the knowledge of a less-known beaked whale and provide evidence of the pathobiological response caused by O. macrorchis for the first time.