Gastrointestinal Lymphoma in a Captive North American River Otter, Lontra canadensis
IAAAM Archive
Shari Hanson1; Kathy Heym Kilgore1; Ilze K. Berzins1; Barbara Sheppard2
1The Florida Aquarium, Tampa FL, USA; 2Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA


A thirteen-year-old female North American river otter (Lontra canadensis) ("Rose") had a history of poor appetite, occasional diarrhea and vomiting, and weight loss over a several month period. The otter was a wild caught orphan and had been a resident of The Florida Aquarium for over 12 years and produced two litters of pups while in captivity.

The otter had been placed under general anesthesia in February 2006 for a physical examination, routine blood work (complete blood count, chemistry profile, heartworm test) and dental cleaning. Routine abdominal, thoracic and skull radiographs were also performed. At that time "Rose" weighed 6.8 kg (a normal otter should weigh between 7.5 to 8.5 kg). The only abnormality noted on physical examination was a purulent vulvar discharge that was subsequently cultured. She had had multiple bouts with this in the past, and each episode was successfully treated with oral antibiotics. No obvious uterine enlargement was noted on abdominal radiographs but heavy growth of Escherichia coli and a beta hemolytic Streptococcus were isolated from culture of the vaginal discharge. Blood results were unremarkable.

For several weeks before and a week after her annual exam, "Rose" was intermittently lethargic and inappetant, with occasional loose stools. As she was no longer part of the breeding program due to her age, the decision was made to spay her to eliminate the possibility of pyometra. A routine ovariohysterectomy was performed. The uterus appeared only slightly enlarged and had a small amount of mucoid fluid within the uterine horns; however, histopathology was normal. A 10-day course of broad-spectrum antibiotics was initiated post surgery.

Over the next several weeks, "Rose's" appetite remained irregular, her weight decreased, and she continued to have occasional bouts of loose stools with mucus and/or blood. Weekly fecal exams revealed no parasites, but occasional increases in bacterial spores (suggestive of Clostridium sp.) were noted (>10-25 spores/hpf). Fecal cultures were negative for Campylobacter, Yersinia, Salmonella, and Shigella species. Clostridium perfringens enterotoxin assay was also negative. She was treated for presumptive Clostridial bacterial overgrowth with metronidazole and increased dietary fiber for 7 days with slight improvement of symptoms. A week later bloody mucoid diarrhea recurred. An injection of procaine penicillin G was give intramuscularly, and the oral antibiotic was changed to sulfadimethoxine (Albon® liquid) due to ease of administration. "Rose" had become increasing difficult to medicate orally due to her poor appetite. Bismuth subsalicylate orally was added to reduce possible endotoxin absorption, and an injection of Clostridial antiendotoxin was administered. She was offered an increasing variety of foods to try and stimulate her appetite, which met with limited success. After two weeks without significant improvement, a course of prednisone was initiated for possible inflammatory bowel disease.

Ten days later, her weight had dropped to 4.3 kg, down 2.5 kg from twelve weeks earlier. The decision was made to perform an abdominal exploratory; however, she was found dead in her kennel on the morning of the scheduled surgery. At necropsy, an approximately 3-cm area of slightly pale signet ring-shaped, thickening was found constricting the intestinal lumen to less than half the diameter of adjacent intestine. Several other areas of thickening in the intestine and possible enlargement of mesenteric lymph nodes were also noted.

A round cell tumor was suspected from examination of impression smears of thickened intestinal wall tissue. On histopathology of the affected intestinal tissue, hypercellular neoplastic round cell infiltrates were found to expand and disrupt all layers of the bowel wall. Individual cells had moderately sized nuclei with 1-3 nucleoli and a small amount of cytoplasm with distinct cytoplasmic borders. The histopathology of the mesenteric lymph node revealed hypercellularity with possible neoplastic infiltrates and minimal organized lymphoid elements. Diffuse, moderate, lymphoid depletion was found in the spleen. Histopathology results confirmed the clinical diagnosis of round cell sarcoma (presumptive lymphoma) of the small intestine. Immunohistochemistry testing indicated the tumor was lymphoma, likely of T-cell origin.

Neoplasia has not been previously reported in North American river otters (Lontra canadensis). In general, the occurrence of lymphoma has not been well documented in the family Mustelidae. One exception is the domestic ferret (Mustela putorius furo) where lymphoma is relatively common1,2 may be linked to a retrovirus.3,4 Isolated cases have been reported in a sea otter (Enhydra lutris),5 European badger (Meles meles)6 and striped skunk (Mephitis mephitis).7


1.  Erdman SE, FM Moore, R Rose, JG Fox. 1992. Malignant lymphoma in ferrets: Clinical and pathological findings in 19 cases. Journal of Comparative Pathology 106: 37-47.

2.  Coleman LA, SE Erdman, MC Schrenzel, JG Fox. 1998. Immunophenotypic characterization of lymphomas from the mediastinum of young ferrets. American Journal of Veterinary Research 59: 1281-1286.

3.  Erdman SE, SA Brown, TA Kawasaki, FM Moore, X Li, JG Fox. 1996a. Clinical and pathological findings in lymphoma in ferrets: 60 cases (1982-1994). Journal of the American Veterinary Medical Association 208: 1285-1289.

4.  Erdman SE, PJ Kanki, FM Moore, SA Brown, TA Kawasaki, KW Mikule, KU Travers, SF Badylak, J G Fox. 1996b. Clusters of malignant lymphoma in ferrets. Cancer Investigation14: 225-230.

5.  Kim JH, BH Kim, JH Kim, MJ Yoo, DY Kim. 2002. Lymphoma in a sea otter (Enhydra lutris). Journal of Wildlife Diseases 38: 616-617.

6.  Mutinelli F, M Vascellari, E Melchiotti. 2004. Mediastinal lymphoma in a Badger (Meles meles). Journal of Wildlife Diseases 20: 129-132.

7.  Smith DA, IK Barker. 1983. Four cases of Hodgkin's disease in striped skunks (Mephitis mephitis). Veterinary Pathology 20: 223-229.

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Shari Hanson

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