Abstract

Blastomyces dermatitidis is a saprophytic yeast found primarily in the Mississippi, Missouri, and Ohio river valleys, the mid-Atlantic states, and southern Canada.³ The infectious mycelial phase occurs in the soil and in culture.³ Blastomycosis develops most frequently in areas exposed to high humidity, fog, and sandy, acidic soils near bodies of water.³ Most clinical cases occur from point source exposure and are frequently diagnosed in autumn.³ Transmission is from inhalation or contamination of open wounds with spores from the environment.³ 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 rarely described in marine mammals.^2,4 Cases involving blastomycosis in marine mammals have been reported in a captive Stellar sea lion,⁵ a captive dolphin,⁴ and two captive California sea lions¹. The two recently described cases of blastomycosis in captive sea lions were located at the Indianapolis Zoo.¹ This report describes blastomycosis in a captive walrus, also at the Indianapolis Zoo.

A 6-year-old male walrus presented in July 2001 with mild inappetence and lethargy. Common differential diagnoses for such a presentation in walrus include seasonal fluctuations in food intake and behavior, tusk infection, or primary gastrointestinal disorder. The presence of very mild clinical signs and no obvious tusk involvement resulted in the decision to closely observe the individual rather than initiate more invasive diagnostic procedures or treatment. Occasional coughing was reported combined with mucus present in the nostrils 6 days after the initial behavioral change, thus, adding respiratory disorder to possible differential diagnoses. A 2-week period followed during which the walrus exhibited normal attitude and behavior intermixed with recurring inappetence, mild lethargy, and irritability. The continued presence of intermittent clinical signs prompted noninvasive sample collection for diagnostic evaluation. On August 1, aerobic culture of nasal mucous samples revealed moderate growth of Serratia marcescens, Pseudomonas, and Enterobacter aerogenes. No pathogenic anaerobes or fungi were isolated. Cytology of the mucus was unremarkable. Fecal analyses were within normal limits. Due to the presence of respiratory signs and a history of pinniped blastomycosis at Indianapolis Zoo, oral orbifloxacin (2890 mg, PO, Q 24 hours; Orbax^®, Schering-Plough Animal Health Corp., Union, NJ, USA) and itraconazole (2900 mg, PO, Q 12 hours; Sporanox^®, Janssen Pharmaceutica Products, Titusville, NJ, USA) were initiated. Unfortunately, the animal continued to decline, and anorexia precluded successful administration of oral antimicrobials. Ketoprofen (800 mg; Ketofen^®, Fort Dodge Animal Health, Fort Dodge, IA, USA) was administered IM once to relieve any inflammation that could be occurring. This resulted in only a temporary improvement in activity and consumption of oral antimicrobials. The walrus was immobilized on August 4 in order to perform complete physical exam, survey radiographs, endoscopy, and bronchoscopy. Bronchoscopy revealed the presence of purulent exudate originating from the right cranial bronchus. Cytology of the bronchial exudate revealed marked suppurative inflammation with mild hemorrhage, lacking the presence of a causative organism. No pathogenic bacteria or fungi were isolated on culture. Thoracic radiographs were suggestive of bronchopneumonia primarily of the right cranial lung lobe. Due to anesthetic complications, the animal was recovered prohibiting radiographs of the left lung fields and abdomen. Hemogram obtained during examination revealed the presence of a profound leukocytosis (47,500) with a mild left shift. Fungal antibodies to Aspergillus, Blastomyces, Histoplasma, and Coccidioides were not detected in serum. Ceftiofur sodium (Naxcel^®, Pharmacia & Upjohn Company, Kalamazoo, MI, USA) was initiated at 250 mg IM once daily as well as amikacin sulfate (Amiglyde-V^®, Fort Dodge Animal Health, Fort Dodge, IA, USA) at 2775 mg IM twice daily for suspected bacterial pneumonia. One week following initial work-up, there was moderate improvement in attitude and food intake facilitating some consumption of itraconazole. However, 9 days following anesthesia and diagnostic testing, the walrus presented with anorexia, severe lethargy, and significant unilateral bloat, predominantly involving the right cranial third of the body. Continued deterioration resulted in a second immobilization and general anesthesia for further diagnostic testing and possible exploratory surgery. During surgical preparations, the walrus became apneic with bradycardia, arrhythmias, and ultimately asystole. Attempts to revive the patient were unsuccessful. Hemogram at the time of death revealed leukocytosis. Blastomyces antibodies were present in serum collected on the day of death. Urine histoplasma antigen was negative at the time of death.

Exterior examination at necropsy revealed profound pitting emphysema from the right muzzle caudad to the right caudal body. Gross findings included hemoperitoneum, profound subcutaneous, mediastinal, pulmonary, and retroperitoneal emphysema, pyothorax, hemothorax, generalized consolidation of all lung lobes, and variably sized tan nodules in all lung lobes. Wright-stained impression smears of lung lesions obtained at necropsy revealed abundant budding yeasts consistent with Blastomyces sp. Aerobic, anaerobic, and fungal culture analyses of thoracic fluid obtained at necropsy revealed only Cladosporium sp.

Histologic examination revealed severe granulomatous and necrotizing pneumonia and mediastinitis with intralesional yeasts. The yeasts were spherical, 18–30 microns in diameter, and had a thick cell wall consistent with Blastomyces dermatitidis. The heart had moderate interstitial fibrosis with myofiber degeneration. Diffuse hepatic lipidosis and mild multifocal neutrophilic hepatitis with Kupffer cell activation was also observed. Acinar cells of the pancreas were atrophic (consistent with suboptimal nutritional status).

The Indianapolis Zoo is located directly adjacent to the White River within the Ohio River valley. Each of the three blastomycosis cases in pinnipeds at the Indianapolis Zoo have been temporally associated with major construction projects involving excavation. Therefore, prophylactic administration of antifungal drugs during such activities in the future might be prudent. Trained behaviors such as voluntary blood collection, active expulsion of respiratory secretions, and nebulization may aid in earlier detection of disease and facilitate effective therapy.

Literature Cited

1.  Garner, M.M., N. Kapustin, J.S. Proudfoot, J. Wojcieszyn, C.C. Wu. 2000. Fatal blastomycosis in two captive sea lions. In: Proc Annu Meet Am Assoc Zoo Vet. New Orleans, Louisiana. 192–193.

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4.  Sweeney, J.C., G. Migaki, P.M. Vainik, R.H. Conklin. 1976. Systemic mycoses of marine mammals. J Am Vet Med Assoc. 169:946–948.

5.  Williamson, W.M., L.S. Lombard, R.E. Getty. 1959. North American blastomycosis in a northern sea lion. J Am Vet Med Assoc. 153:513–515.