An emaciated adult female offshore killer whale (Orcinus orca), at least 40 years of age, stranded dead in Portage Bay, Alaska. At postmortem examination, 30–40 parasitic copepods (Pennella balaenopterae) were found embedded within the blubber, extending from the head region along the lateral aspect of the body to the peduncle with increased densities around the genital and mammary slits. These copepods presented as long (up to 12 cm), thin (~ 0.2 cm diameter) dark brown to black, hard and brittle cylindrical structures extending from discrete circular defects of the epidermis. On cut section, Pennella were found embedded within the deep dermis and blubber layer, though penetration into the skeletal muscle was not appreciated. Histologic evaluation of affected skin and blubber revealed a chronic pyogranulomatous response surrounding the copepods. There was also evidence of concurrent bacterial infection in some of attachment sites. Death of this orca was attributed to severe periodontal disease and subsequent inanition and debilitation, though other presumably age-related disease processes likely contributed to its demise. Penellid ectoparasitism has been reported in numerous cetacean species, including dolphins and baleen whales in addition to rare reports in pinnipeds.1-3,5-9 To our knowledge, this is the first report of this ectoparasite in Orcinus. While low numbers of penellid copepods are detected in seemingly healthy cetacean hosts, heavy infestations particularly of delphinid species have been correlated to poor health status and disease states including emaciated body condition, lymphoid depletion, concurrent infections (viral, bacterial, fungal), and high contaminant loads.1,4,7,10 As such, continued quantitative and qualitative assessment of Pennella balaenopterae infestations during photographic identification surveys of free-ranging animals and postmortem examinations of stranded individuals is needed to better elucidate the correlation of these parasites to health and disease status of various cetacean species.
The authors would like to thank Aleria Jensen, Sadie Wright, Chris and Dr. Heidi Pearson, Dr. Katie Savage, Don Holmes, Scott Roberge, and Paul Nicklen for coordination and assistance with the necropsy. We thank Drs. Judy St. Leger, Stephen Raverty, and Kathy Burek Huntington for their expertise and advice in this case, and Graeme Ellis for identifying the whale (O059) and providing details on its history. Finally, thanks to Roy Brown at Histology Consultation Services for tissue processing and slide preparation and Tracey Goldstein and staff at UC Davis Marine Ecosystem Health and Disease Surveillance Laboratory for microbiology testing.
* Presenting author
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