1Omaha’s Henry Doorly Zoo and Aquarium, Omaha, NE, USA; 2College of Veterinary Medicine, Western University of Health Sciences, St. Pomona, CA, USA; 3SeaWorld, San Diego, CA, USA; 4College of Veterinary Medicine, Cornell University, Ithaca, NY, USA; 5Forth Worth Zoo, Fort Worth, TX, USA; 6Brookfield Zoo, Chicago Zoological Society, Brookfield, IL, USA; 7National Zoological Park, Smithsonian Conservation Biology Institute, Washington, DC, USA; 8Zoological Pathology Program, University of Illinois, Brookfield, IL, USA
Abstract
Asian small-clawed otters (Aonyx cinereus, ASCO) and North American river otters (Lontra canadensis, NARO) are two otter species commonly displayed at zoos and aquaria throughout the United States. While there have been a small number of case reports and retrospective studies involving these species, many have focused on free-ranging individuals and do not represent otters in human care.1-3 Necropsy reports from 93 individuals, 71 ASCO, and 22 NARO, that died or were euthanized between 2000 and 2020 and housed at 10 different institutions were evaluated. Individuals in this study with known ages ranged between 2 months and 21 years of age with 47 females, 45 males, and 1 unknown sex. Common causes of morbidity and mortality included malignant neoplasia (n=29), chronic kidney disease/urolithiasis (n=27), degenerative joint disease (n=13), and cardiovascular disease (n=10).
The most common neoplasms included lymphoma (n=6), bronchioalveolar carcinoma (n=5), cutaneous malignant melanoma (n=3), and mammary gland adenocarcinoma (n=3). Fifteen (88%) individuals with these neoplasms had evidence of often widespread metastatic disease. The primary site of lymphoma in NARO was the intestine as noted in a previous report,4 whereas in ASCO, lymphoma was found primarily in the spleen, liver, kidney, and lymph nodes. Chronic kidney disease (CKD) was most common in ASCO (24/71, 34%) and 92% of these individuals had concurrent nephrolithiasis. Nephroliths were present in only two NARO. Four ASCO with CKD and nephrolithiasis succumbed to pyelonephritis. Euthanasia related to degenerative joint disease occurred in both species and was present in the stifle joints (n=7), vertebral column (n=6), tarsal joints (n=2), elbow joints (n=2), and or coxofemoral joints (n=1). Cardiovascular disease was associated with biventricular congestive heart failure (CHF) in all three affected ASCO and restricted to right sided (n=2) or left sided (n=1) CHF in NARO. Interestingly, severe gastrointestinal hemorrhage was a primary cause of death in nine (13%) ASCO, five of which had undergone an anesthetic procedure within 5 days of death. Common nonlethal comorbidities included periodontal disease (n=30) and degenerative joint disease (n=21) among others.
Common causes of morbidity and mortality in both species correlated to the predominance of older adult and geriatric animals in the studied population. Chronic kidney disease, often associated with nephrolithiasis, has been well described in managed ASCO5 and also in free-ranging NARO6.
While sporadic case reports of individual neoplasms have been described in both species,7-10 multiple benign and malignant neoplasms were identified indicating that neoplasia plays a more prominent role than previously suspected in the morbidity and mortality of ASCO and NARO in human care, particular in aged populations.
Acknowledgements
The authors wish to thank the husbandry and veterinary staff of the contributing institutions. Thanks to the pathologists, histotechnologists, and diagnostic laboratory staff for their contributions to this study.
*Presenting author
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