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Diseases of Aquatic Organisms

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DAO 127:177-192 (2018)  -  DOI:

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

Shotaro Nakagun1,2,*, Akira Shiozaki3, Mari Ochiai4, Ayaka Matsuda5, Yuko Tajima6, Takashi Matsuishi5, Kenichi Watanabe1, Noriyuki Horiuchi1, Yoshiyasu Kobayashi1

1Laboratory of Veterinary Pathology, Department of Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan
2United Graduate School of Veterinary Sciences, Gifu University, Gifu, Gifu 501-1193, Japan
3Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Nagasaki, Nagasaki 852-8521, Japan
4Center for Marine Environmental Studies, Ehime University, Matsuyama, Ehime 790-8577, Japan
5Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan
6Department of Zoology, National Museum of Nature and Science, Tsukuba, Ibaraki 305-0005, Japan
*Corresponding author:

ABSTRACT: Beaked whales are among the least known group of cetaceans, and information regarding their pathology and parasitology is 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 little-known beaked whale and provide evidence for the first time of the pathobiological response caused by O. macrorchis.

KEY WORDS: Liver pathology · Bile duct · Brachycladiidae · Ziphiidae · PCBs · Stomach contents · Cetacean stranding

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Cite this article as: Nakagun S, Shiozaki A, Ochiai M, Matsuda A and others (2018) Prominent hepatic ductular reaction induced by Oschmarinella macrorchis in a Hubbs’ beaked whale Mesoplodon carlhubbsi, with biological notes. Dis Aquat Org 127:177-192.

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