Abstract

A variety of systemic mycoses have been reported in captive and free-ranging marine mammals. Histoplasmosis, caused by the dimorphic fungus Histoplasma capsulatum, primarily presents as a pulmonary disease but occasionally fatal disseminated disease can occur.^1,2 The fungus is associated with a distinct geographic distribution of humid temperate climates and is considered endemic to the Mississippi-Ohio river basin.^2,3 Documented cases of histoplasmosis in marine mammals are rare, with only one reported case in a free-ranging animal.⁴

A case of systemic histoplasmosis in a 4-month-old male northern sea otter (Enhydra lutris kenyoni) pup is described. The animal originally stranded in Homer, Alaska at approximately 16 days old and was admitted for rehabilitation at the Alaska SeaLife Center. On initial assessment, this animal was dehydrated, malnourished, and hypoglycemic but quickly stabilized. Approximately 4 months later, the pup began acutely exhibiting weight loss, hyporexia, vomiting, pyrexia, and diarrhea. Despite supportive care, the pup succumbed to death roughly 36 hours after the onset of clinical signs. Necropsy and histopathology revealed severe necrotizing hepatitis, severe histiocytic interstitial pneumonia, severe histiocytic lymphadenitis, and mild histiocytic enteritis with intralesional organisms. The animal was diagnosed with a systemic histiocytic inflammatory process associated with large numbers of intracytoplasmic organisms most consistent with Histoplasma sp. and H. capsulatum was confirmed by PCR and sequencing. In addition, Erysipelothrix rhusiopathiae was cultured in the brain, bile, and a gastric lymph node resulting in a bacteremia. Nasal and rectal swabs tested negative for coronavirus, SARS-CoV-2, and influenza. This is the first confirmed report of systemic histoplasmosis in a sea otter pup. Furthermore, it is the second reported case in a sea otter in Alaska despite being far outside the known distribution of this pathogen.4 The route of transmission to this region is unknown, and the implications of increased cases of histoplasmosis to sea otter population health have not yet been determined.

Acknowledgements

The authors wish to thank the Alaska SeaLife Center Wildlife Response for their contributions in animal care to this case and their daily efforts towards marine animal rescue and rehabilitation. The technical staff at the University of Illinois Veterinary Diagnostic Laboratory, the University of California Davis Marine Ecosystem Health Diagnostic and Surveillance Laboratory, and the Alaska Veterinary Pathology Services are gratefully acknowledged. Marine animal rescue and rehabilitation performed under agreement with the United States Fish and Wildlife Service permit MA73418B-1.

Literature Cited

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2.  Jensen ED, Lipscomb T, Van Bonn B, Miller G, Fradkin JM, Ridgway SH. 1998. Disseminated histoplasmosis in an Atlantic bottlenose dolphin (Tursiops truncatus). J Zoo Wildl Med. 29(4):456–60.

3.  Huckabone S, Gulland F, Johnson S, Colegrove K, Dodd E, Pappagianis D, Dunkin R, Casper D, Carlson E, Sykes J, Meyer W, Miller M. 2015. Coccidioidomycosis and other systemic mycoses of marine mammals stranding along the central California, USA coast: 1998–2012. Journal of wildlife diseases. 51. 10.7589/2014–06–143.

4.  Burek-Huntington K, Gill V, Bradway D. 2014. Locally Acquired Disseminated Histoplasmosis in a Northern Sea Otter (Enhydra lutris kenyoni) in Alaska, USA. Journal of wildlife diseases. 50. 10.7589/2013–11–288.