1Northwest ZooPath, Snohomish, WA, USA; 2Relief Veterinary Services, Indianapolis, IN, USA; 3Indianapolis Zoo, Indianapolis, IN, USA; 4IHC Services, Smithville, TX, USA; 5Microbiology Service, Animal Disease Diagnostic Lab, Purdue University, IN, USA
Abstract
Blastomyces dermatitidis is a dimorphic fungus and the etiologic agent of North American blastomycosis.1 Blastomycosis commonly occurs as a primary pulmonary infection with occasional spread to other viscera.1,3 The disease has been described most often in dogs, cats, horses, and humans, but is apparently rare in marine mammals.1-3 It has been reported once in a captive Stellar sea lion3 and once in a captive dolphin2. This report describes two cases of fatal blastomycosis in long-term captive California sea lions at the Indianapolis Zoo. Sea lion 1 was an approximately 29-year-old long-term captive male, kept at the Indianapolis Zoo for 8 years prior to death in 1996. The animal had a chronic history of clouded corneas attributed to aging. Two weeks prior to death it developed lethargy and a tense abdomen and urinalysis revealed hematuria and pyuria. Aerobic culture of the urine revealed Escherichia coli, Klebsiella pneumoniae, and Edwardsiella sp. The sea lion did not respond to antibiotic therapy and died following a brief period of tachypnea. Necropsy revealed spherical nodules in the skin, lungs, on the pleural surfaces, and in a mesenteric lymph node. Mycotic culture of fluid from the chest revealed Blastomyces dermatitidis, and the identification was confirmed by PCR probe of cultured fungus. The animal also had chronic renal disease. Sea lion 2 was a captive-born 13-year-old female that had been at the Indianapolis Zoo 1 year prior to death in 1998. The animal had a chronic history of skin abrasion over the flippers, pectoral, and pelvic areas that was believed to be associated with rubbing in the tank. The sea lion also had a long-term history of clouded corneas believed to be associated with osmoregulatory disturbances due to inappropriate water quality. The animal developed a 2-week history of lethargy, inappetence, and tachypnea. During this time, serology was positive for Blastomyces antibody, and the animal was treated for 3-days prior to death with itraconazole (Sporanox® itraconazole capsules 100 mg, Janssen Pharmaceutica Inc., Titusville, NJ, USA; 200 mg POQ 24 h × 2 days, then 400 mg BID × 1 day). After a brief mild improvement in clinical signs, the animal died. Necropsy revealed multiple nodules in the lungs and pleura. Blastomyces sp. was isolated from mycotic culture of a pleural lesion. Histopathology of both animals revealed granulomatous inflammation associated with yeasts in lung and mesenteric lymph node from both animals. Sea lion 1 also had mycotic granulomas in the spleen. Sea lion 2 had mycotic granulomas in tracheal-bronchial lymph node, mammary gland, skin, skeletal muscle, and kidney. The granulomas were comprised predominantly of macrophages and multinucleate giant cells with fewer neutrophils. Extracellular and intracellular yeasts were frequently detected in areas of inflammation. The yeast was round and 8–20 µm, with broad based budding, and a thick-walled capsule. Immunohistochemistry was positive for Blastomyces sp. in sections of affected lung from both animals.
Because lung was the most affected tissue, respiratory tract was presumed to be the primary route of infection, but entry through skin abrasions may also have been possible. Aging, captive stressors, and perhaps concurrent antibiotic therapy (sea lion 1) may have compromised immune function in these animals, predisposing them to blastomycosis. In the United States, Blastomyces dermatitidis is endemic in the environment of the Mississippi, Missouri, and Ohio River drainages. Blastomycosis should be considered a differential diagnosis for respiratory disease in captive sea lions from these areas.
Acknowledgments
We appreciate the technical expertise of Histology Consulting Service for histology slides and the Indiana Veterinary Diagnostic Laboratory for Blastomyces serology.
Literature Cited
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