Gross Findings: On external examination, the oral mucous membranes and the conjunctiva were pale. Many ticks were present on the carcass. The ribs, vertebrae, hips, scapulae, and skull bones were prominent. Full body radiographs revealed three areas of bony proliferation with cortical destruction on the front legs (right distal radius, right mid-femur, and left proximal radius) (Fig. 1). On internal examination, there was scant subcutaneous fat and serous atrophy of epicardial fat. The internal organs were markedly autolyzed. A 0.5 x 0.5 cm perforation was present in the wall of the distal esophagus, and a plastic bag was lodged tightly in the cardia of the stomach adjacent to the esophageal sphincter (Fig. 2). Multiple lytic lesions were present in the atlas (Fig. 3).

Histopathological Findings: All tissues were in a state of advanced autolysis. However, it was possible to detect multiple extracellular 8-20 micron yeasts with prominent broad-based budding, consistent in morphology with B. dermatitidis, in the lung, brain, and in areas of osteomyelitis (Fig. 4).

Morphologic Diagnoses:

1. Acute, multifocal, superficial to transmural esophageal ulceration.
2. Subacute, marked, multifocal osteomyelitis with intralesional yeasts

Disease: Blastomycosis

Etiology: Blastomyces dermatitidis or gilchristi.

Distribution: B. dermatitidis has a relatively wide distribution in North America, including the Mississippi, Missouri, and Ohio river valleys; the Middle Atlantic states; the Pacific Northwest; Southern Saskatchewan; Manitoba; Quebec; and Ontario. B. gilchristi is found mainly in the northern USA and Canada.

Seasonality: No seasonality has been described.

Host range: Dogs and humans are most commonly affected. Cases also occur in cats, horses, ferrets, deer, and many wildlife species. Blastomycosis has been reported in wild wolves in Canada and in Minnesota and Wisconsin, USA.

Transmission: Blastomyces sp. is a dimorphic environmental fungus. The infective mycelial phase is most often found in sandy soil that is rich in organic material and close to fresh water. Infection occurs through inhalation of aerosolized fungal spores. Once inhaled, the organism develops into a yeast form that can infect the lungs and may disseminate widely throughout the body.

Clinical signs: Clinical findings may be non-specific (anorexia, weight-loss, fever, lymphadenopathy), and/or may reflect the site or sites of infection. Cough and respiratory distress commonly occur. Disseminated infection typically presents as foci of osteomyelitis, ulcerated or proliferative skin lesions, and/or ocular lesions (such as uveitis and corneal edema). Central nervous system involvement is relatively rare.

Pathology: Multifocal pyogranulomas are found where typical broad-based budding, 8-20 micron yeasts are present in infected tissues. Osseous invasion of Blastomyces is characterized by lytic destruction and periosteal reaction, accompanied by granulomatous infiltrates in areas of necrosis. Pathologic fractures may occur. Dissemination to the central nervous systems can result in meningitis and epidural or brain abscesses.

Diagnosis: A high index of suspicion is necessary in areas where blastomycosis occurs as clinical findings may be non-specific. In animals with respiratory signs, chest X-rays typically show multiple nodular infiltrates throughout the lung fields. Antemortem diagnosis can be confirmed by identification of characteristic yeasts in tissue impressions, fine needle aspirates, fluids, or biopsies. In addition, antigen testing of urine is sensitive; but may cross-react with Histoplasma sp. fungi.

Public health concerns: In general, human cases of blastomycosis result from direct inhalation of environmental spores. Coughing animals do not transmit the disease to humans. However, care should be taken when caring for animals with draining or ulcerated skin lesions, as direct cutaneous infection may occur by needlestick or wound contamination. Additionally, the mycelial phase of the fungus may form in bandaged skin lesions and produce aerosolized infective spores; therefore, wounds should be left unbandaged and proper protective equipment should be worn when caring for these patients. Attempts to culture B. dermatitis should only be undertaken in laboratories with appropriate biosafety controls.

Wildlife population impacts: Unknown

Management: Itraconazole (5 mg/kg given orally, once daily, long-term treatment) is indicated in affected individuals. Prognosis is best when the infection is identified early in the course of the disease.

 References:

• Armstrong CW, Jenkins SR, Caufman S, Kerkering TM, Rouse BS, Miller GB. 1987. Common-Source Outbreak of Blastomycosis in Hunters and Their Dogs. J Infect Dis 155: 568–70. https://doi.org/10.1093/infdis/155.3.568
• Baumgardner DJ, Paretsky DP, Baeseman JZ, Schreiber A. 2011. Effects of season and weather on blastomycosis in dogs: Northern Wisconsin, USA. Medical Mycology 49: 49–55. https://doi.org/10.3109/13693786.2010.488658
• Mazi PB, Rauseo AM, Spec A. 2021. Blastomycosis. Infect Dis Clin North America, 35: 515-530. https://doi.org/10.1016/j.idc.2021.03.013
• Mruthyunjayappa S, Leal SM. 2022. Blastomyces. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/microbiologyblastomyces.html.
• Schwartz IS. 2017. Blastomycosis in Mammals. Emerging and Epizootic Fungal Infections in Animals. 14:159–76. https://doi.org/10.1007/978-3-319-72093-7_8
• Thiel RP, Mech LD, Ruth GR, Archer JR, Kaufman L. 1987. Blastomycosis in wild wolves. J Wildl Dis. 1987 23:321-323. https://doi.org/10.7589/0090-3558-23.2.321