Abstract

An adult male sea otter was observed hauled out for two consecutive days near the dock of a seafood processing plant in the Seward Small Boat Harbor, Seward, Alaska in April of 1998. The otter was lethargic and unable or unwilling to avoid traffic and human contact. The animal was herded into a transport cage by rehabilitation staff and transported to a holding pen at the Alaska SeaLife Center where it readily ate smelt, clams and herring and began vigorous whole body grooming in the salt water pool. The otter was observed sleeping on the haul out deck at 0600 the next morning but was found comatose and hypothermic at 0800. Veterinary examination at that time revealed a deep body temperature of 74°F, a heart rate of 60, mucous membranes pink with good capillary refill and a loss of waterproofing of the hair coat. The left eye was opaque with a shrunken globe (phthisis bulbi) and the right eye was exophthalmic with a constricted pupil that was nonresponsive to light. Laboratory facilities were not available as the SeaLife Center was still under construction, but a diagnosis of hypoglycemia and hypothermic shock was presumed and treatment begun with a warmed intravenous bolus of 10% dextrose and dexamethasone followed by rapid infusion of 5% dextrose in saline via an indwelling jugular catheter. The otter was towel dried and hand held hair dryers used to warm the flippers and further dry the hair coat. Body temperature gradually increased and voluntary movement was observed, causing the jugular catheter to be dislodged. Intramuscular enrofloxacin and oral ranitidine were administered. The otter was still weak and disoriented and passed tan to brown mucoid stools and large volumes of urine repeatedly. An apparent second hypoglycemic episode with mild seizure activity occurred at 1400. Treatment with bolus 20% dextrose intravenously was followed by intravenous and subcutaneous 5% dextrose. Behavior became increasingly more coordinated and the otter was returned to a transport cage when body temperature reached 96° F and he ate small pieces of clam that were offered with tongs. The otter began to pass brown mucoid stools with pieces of undigested clam meat within 3 hours and then vomited a tan liquid. He slept for prolonged periods alternating with brief episodes of vocalization and lethargic grooming of the face and forelegs. Mylanta and a clam gruel were tube fed and subcutaneous 5% dextrose in saline repeated at 4 hour intervals through the night but the otter gradually became hypothermic again and began fine muscle twitching and labored, grunting respiration. Agonal seizures were observed about 0500 followed rapidly by complete cardiovascular arrest.

Immediate post mortem examination of the abdominal cavity revealed a large volume (~600 ml) of thin purulent fluid containing large numbers of motile nematode parasites and several tapeworms free in the coelomic cavity. The omentum was dark red and attached by a fibrinous adhesion to a 6 by 8 cm site on the serosal surface of the greater curvature of the stomach. The adhesion peeled off easily revealing a roughened serosal surface but no obvious perforation. Incision into the stomach adjacent to the adhesion site revealed a 3 by 5 mm pink ulceration with a mass of thin nematode parasites imbedded into the ulcerated surface almost totally filling the lesion and resembling a tuft of hair. Multiple small nematodes of varying diameter and length and several more tapeworms were also noted in the stomach. The small bowel contained 1-2 tapeworms, 2-4 acanthocephalids and 1-3 nematodes in each of three 20 cm segments. The gall bladder contained small numbers of flukes. Other tissues were unremarkable except for enlarged, turgid and reddened abdominal lymph nodes and congestion and reddening of the lungs with pink froth in the airways.

Histopathology of the gastric lesion confirmed chronic active gastritis with a perforating ulcer. Nematode fragments were seen embedded in the submucosa. The parasites were tentatively identified as Pseudoterranova decipiens.

Discussion

The diet of sea otters in Prince William Sound normally includes a variety of bivalves, crustaceans and other small benthic organisms. Occasional sightings have been reported of otters eating salmon or other fish. It is unclear if fish eating is a result of individual habit or due to lack of availability of shellfish and other usual prey. Recent publications have suggested that sea otters feeding on fish, and especially fish carcasses from processing plants, are increasingly infested with an unusual nematode parasite (possibly Anisakis or Pseudoterranova spp.). Larva of Pseudoterranova spp. are commonly found in the muscle and visceral tissue of pacific cod, pollock and bottom dwelling flat fishes in Prince William Sound. Anisakiasis is a well-recognized syndrome in humans after eating raw (sushi) or poorly cooked fish infested with these larvae. The authors have previously observed slender parasites, similar to those found in this animal, free in the abdominal cavity of sea otter carcasses from Prince William Sound. This otter may have become infested after feeding on the carcasses of fish at the outflow of the processing plant in the Seward harbor. The large burden of an abnormal parasite for this host resulted in gastric perforation, reflux and migration of these and other parasites into the peritoneal cavity and subsequent septic peritonitis. Septic shock, hypoglycemia and hypothermia were terminal events only temporarily alleviated by medical treatment and supportive care. Surveys of parasite loads of otters in Prince William Sound are currently part of the US Fish and Wildlife Service Biosampling Program but include only location and estimates of numbers of parasites. Collection and identification of parasite species, especially nematode parasites, may add significant insight into the health, diet and risk factors of sea otters in this geographical area.

Acknowledgements

The authors wish to thank Dr. Murray Dailey of The Marine Mammal Center, Sausalito, California for his assistance in identifying the nematodes associated with the gastric ulcer in this case and Brenda Ballachy and Carol Gorbics and their staff at the US Fish and Wildlife Service Office of Marine Mammal Management in Anchorage, Alaska for their advice and assistance.