1 year old male domestic shorthair, Felis domestics, feline.The cat presented with a 1month history of ataxia, head tilt, and aggression towards other animals and people. Prior to death, the cat was capable of eating and drinking.
The animal presented in good body condition and postmortem preservation. The only significant
gross finding was a 1.2 cm in diameter well demarcated light brown mass in the rostral portion of the left cerebral hemisphere.
Located within the cerebral neuropil is an expansile, well demarcated area consisting of large numbers of neutrophils, macrophages, and lymphocytes, small amounts of fibrous connective tissue, and variably sized areas of necrosis. Intermixed throughout the lesion are low numbers of 7-2 micrometer round to oval yeast bodies which have thick cell walls, moderate amounts of poorly staining cytoplasm, and round 3-15 micrometer homologous staining nuclei. Some of the yeast bodies display broad based budding. Multiple blood vessels in the neuropil adjacent to the lesion are surrounded by low to moderate numbers of lymphocytes and macrophages. The overlying meninges contain low to moderate numbers of lymphocytes, macrophages and neutrophils, and small amounts of fibrillar acidophilic proteinaceous material.
Severe chronic focal necrotizing pyogranulomatous encephalitis with intralesional yeast. Moderate chronic multifocal meningoencephalitis.
Pathogenic bacteria, viruses, and fungi were not isolated from the brain, lungs, liver, kidneys, or intestines.
Blastomycosis was diagnosed based on the morphological characteristics of the yeast.
Blastomycosis is most-frequently reported in canids and humans, though cases in other domesticated and non-domesticated species are occasionally seen(6). The dimorphic fungi are not commonly isolated from the environment, but are thought to survive in manure and in soil containing decaying vegetation and high moisture content(1). Disease is thought to be initiated by inhalation of B. dermatitis conidia. At body temperatures, conidia transform to the yeast phase which may disseminate and elicit pyogranulomatous inflammatory responses in the lungs,
bones, liver, spleen, lymph nodes, skin, eyes, urogenital tract, and brain(2,4,7). This case is remarkable as the cat presented with neurologic signs accompanied with a distinct cerebral lesion suggestive of neoplasia. Lesions consistent with B. dermatitis were not seen in other organs or tissues.
Cerebrum: Meningoencephalitis, pyogranulomatous, multifocal, severe, with lymphocytic perivascular cuffing and budding yeasts.
The three clinical forms of blastomycosis are primary pulmonary infection, most common in domestic animals, disseminated disease, as in this case, and local cutaneous infection secondary to direct tissue inoculation, which is rare. B. dermatitis has several virulence factors. Blastomyces Adhesion 1 (BAD-1) is a surface protein which mediates adhesion to host cells and modulates immune response, and alpha-glucan protects against killing by macrophages. The adhesion molecules bind to CD14 and complement receptor 3 (CR3) on macrophages and induces activation; however, Blastomyces is not readily phagocytized. Blastomyces initially causes a neutrophilic response, but with the onset of cell mediated immunity, a granulomatous response predominates. Differential diagnosis for this case includes Cryptococcus spp., which often cause a gelatinous toruloma in the brain, and Aspergillus spp., which often causes severe necrotizing vasculitis(3,5).
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