Abstract

On 13 September, 2000, an approximately eight-month old, female, stranded northern elephant seal (Mirounga angustirostris), was recovered from Sand Dollar beach in Santa Cruz County, California. The seal was brought to The Marine Mammal Center in Sausalito, California, for rehabilitation. The seal weighed 55 kg, was lethargic, and approximately 5% dehydrated. Initial physical examination also revealed three raised, ovoid subdermal masses with "stubs" of elongate tubular structures extending from the skin. The largest mass was approximately 12 cm in diameter and located over the dorsal midline of the mid-thoracic region. A second mass of approximately 2 cm in diameter was found over the dorsal midline overlying the sacral vertebrae. The third mass was found on the right flank of the mid-thoracic region and was approximately 6 cm in diameter. Several firm, brown, thin-walled, hollow, tubular structures approximately 3-4 mm in diameter were visible on the surface of the masses. The tubes were found to penetrate up to approximately 3 cm into the mass. The tubular structures were firmly embedded in the mass and could not be easily extracted. All three masses were lanced to reveal between approximately 2 and 6 ml of mucopurulem discharge. Each mass was irrigated with chlorhexidine solution and as much of each tubular structure as possible was removed. Initial complete blood count (CBC) and clinical chemistry analysis were unremarkable.

The masses continued to ooze mucopurulent discharge and did not appear to resolve over the next 12 days. On 25 September, the elephant seal was given 1.08 mg of atropine by intramuscular injection. After approximately 10 minutes, the seal was sedated with 43 mg of a 1"1 mixture of zolazepam and tiletamine (Telazol®) injected intravenously into the extradural sinus. The seal was intubated with a 10 mm diameter endotracheal tube and maintained with 0.5 to 4.0% isoflurane. Incisions were made in all three masses and sharp-blunt dissection was used to explore each area. The masses were found to be firm, tough, and bled very easily. Some mucopurulent debris was found within each mass. Exploration of the masses revealed several tubular structures up to 2 cm in length attached to heads with multiple branching "horns" or anchors of up to approximately 1 cm in length. Each wound was irrigated with chlorhexidine and left open to heal.

The embedded organism was identified as a parasitic copepod of the genus Pennella.

On 4 October a CBC revealed a mild leukocytosis of 35,500 cells/pl (normal range is 10,400 to 28,500 cells/pl). Mucopurulent exudate continued to ooze from two dorsal wounds even though they were regularly irrigated with chlorhexidine. The seal was given 480 mg of trimethoprim- sulfamethoxazole orally twice daily for the next 20 days. On 16 October, the seal was sedated with an intramuscular injection of 3 mg of butorphanol. Moderate amounts of mucopumlent exudate were still present from both dorsal wounds. These were incised and irrigated with chlorhexidine. No tubular structures were evident during exploration of the masses. Bacterial culture of the exudate resulted in growth of Arcanobacterium phocae, Escherichia coli, Edwardsiella tarda, Enterococcus sp., and Proteus mirabilis. Both dorsal masses continued to ooze mucopurulent exudate. The seal was anesthetized again on 6 November with an intravenous injection of 50 mg of zolazepam and tiletamine. Exploration of the masses revealed a single piece of copepod from each area. Both wounds were again irrigated with chlorhexidine and left open to heal. The seal was given a subcutaneous injection of 12 mg of ivermectin.

Small amounts of exudate continued to ooze from the larger dorsal thoracic mass only. The seal was sedated on 29 November with 15 mg of diazepam given intravenously. The wound was scrubbed and explored again to reveal a single 2 cm section of copepod. This wound healed over the next 10 days with no further evidence of exudate.

On 8 December results of a CBC and clinical chemistry were found to be within normal parameters, the animal was eating normally, weighed 87.5 kg, and all masses were healing well. The elephant seal was released on 11 December, 2000.

The life cycle of members of the copepod genus Pennella is not known, however their larval forms have been found on the gills of cuttlefish (Sepia sp.)¹. Pennellids are the largest of the copepods reaching a length of more than 30 cm and tend to invade the circulatory system, sense organs or viscera of fish hosts. Pennellids have been found on whales but do not cause subcutaneous abscesses, as seen in this case.². It appears that the parasite cannot penetrate the keratinized skin of pinnipeds, as it can that of fish and cetaceans. It is suspected that at one time, that this elephant seal had open skin lesions allowing the larval copepods to enter the tissue. Subsequent healing of the wound left only the external bodies (tubules) of the parasites protruding outside the skin. This portion of the body would then produce the eggs to be released into the environment. When examined on recovery, only the "stubs" of these elongate, tubular portions of the parasites were found, indicating that this elephant seal had broken off, by either rubbing or scraping the egg-bearing distal parts of the bodies.

Acknowledgements

The authors thank Shelbi Stoudt, the rescue team and volunteers from the Marine Mammal Center for their help during the study. We also thank Dr. Linda Lowenstine, University of California, Davis, CA, and Dr Bob Kabata, Pacific Biological Station, Nanaimo, B.C., Canada, for their contributions to the understanding of the pathology encountered and verification of copepod identification respectively.

References

1.  Schmitt, W. L. 1968. Crustaceans, University of Michigan Press, Ann Arbor, MI. 204pp.

2.  Dailey, M. D. 1985. Diseases of Mammals: Cetacea, Chapter 7, in diseases of Marine Animals, Vol. IV, Pt. 2, Kinne, O (ed), Biologische Anstalt. Helgoland, Hamburg, 805-847.