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

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.

Histochemical and Immunohistochemical Characterizations of Hepatic Trematodiasis in Odontocetes

“…With the present study, there is a possibility that the interspecies differences observed in the reactions of respective species may have been due to differences in the infecting trematode species: C. oblonga in the harbor and Dall's porpoises and O. macrorchis in the Hubbs' beaked whales. However, the two trematode species only differ morphologically by the presence of the lateral diverticula and are genetically very close (26). In fact, the genetic distance inferred from its mtND3 sequences between O. macrorchis and C. oblonga are closer than that between O. rochebruni within the same genus (26).…”

“…However, the two trematode species only differ morphologically by the presence of the lateral diverticula and are genetically very close (26). In fact, the genetic distance inferred from its mtND3 sequences between O. macrorchis and C. oblonga are closer than that between O. rochebruni within the same genus (26). Therefore, from both morphological and genetic perspectives, we presumed that the host response should naturally be alike.…”

“…On the other hand, Oschmarinella macrorchis has been reported only from the biliary tracts of Stejneger's beaked whales Mesoplodon stejnegeri (25) and Hubbs' beaked whales Mesoplodon carlhubbsi (26), indicating a narrower host range. Descriptions of Oschmarinella-infected liver histopathology have been scarce to date with limited reports of fibrosis and pericholangitis (12,27,28) and a single case report from a Hubbs' beaked whale describing prominent ductular reaction and lack of lymphoid follicles (26). The lesions described in the Hubbs' beaked whale had not been described in hepatic trematode infections of marine mammals before, indicating a possibility of interspecies difference in the response against various trematode species.…”

“…Histopathology of the lesions caused by Campula has been well-documented with hypertrophy of the biliary epithelium, portal fibrosis, cholangitis, pericholangitis, and formation of lymphoid follicles ( 22 – 24 ). On the other hand, Oschmarinella macrorchis has been reported only from the biliary tracts of Stejneger's beaked whales Mesoplodon stejnegeri ( 25 ) and Hubbs' beaked whales Mesoplodon carlhubbsi ( 26 ), indicating a narrower host range. Descriptions of Oschmarinella -infected liver histopathology have been scarce to date with limited reports of fibrosis and pericholangitis ( 12 , 27 , 28 ) and a single case report from a Hubbs' beaked whale describing prominent ductular reaction and lack of lymphoid follicles ( 26 ).…”

CD3 and CD20 co-expression in a case of canine peripheral T-cell lymphoma with prominent cardiac and peripheral nerve involvement

“…For further characterization of the neoplastic lymphocytes, immunohistochemistry was performed on serial sections of the heart and hepatic peripheral nerve bundle according to a protocol described previously. 13 The antibodies used were as follows: monoclonal mouse antibody against CD3 (1:100, clone F7.2.38; Dako, Tokyo, Japan); polyclonal rabbit antibody against CD8 (1:200; Abcam, Tokyo, Japan); polyclonal rabbit antibody against granzyme B (1:400; Spring Bioscience, Pleasanton, CA); polyclonal rabbit antibody against CD20 (1:400; Thermo Fisher Scientific, Fremont, CA); monoclonal mouse antibody against CD79α (ready-to-use, clone JCB117; Dako); and polyclonal rabbit antibody against Pax5 (1:500; Thermo Fisher Scientific). Antigen retrieval involved microwave heat pretreatment at 97°C, for 15 min in citrate buffer solution (pH 6.0) for CD3, CD8, granzyme B, CD20, and Pax5, and in target retrieval solution (pH 6.1; Dako) for 20 min for CD79α.…”