Fungal Diseases
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History. A 2-year-old male Himalayan cat presents with a history of sneezing for the past month. The cat primarily remains indoors, vaccinations are up-to-date, and it has a normal appetite. The owner noticed a mass in the right nares earlier this week, and it appears to be getting larger.

Examination. Vital signs on presentation are temperature 99.6°F, pulse 160 beats/minute, and respiration 30 breaths/minute. On physical examination, the cat is bright, alert, and responsive; ambulatory; and has no evidence of respiratory distress. A 0.5-cm pink nasal mass on the medial aspect of the right nares is observed; it is not ulcerated or bleeding.

Cytologic sampling. The cat is sedated, and fine-needle aspiration of the mass is done for cytologic examination. The veterinarian saves one smear to examine personally and sends the other to the local diagnostic laboratory for pathologic evaluation. See Figures 1 and 2 (Wright's-Giemsa stain).

ASK YOURSELF. . .

• What type of inflammation is present?
• What organism is noted?
• What is your definitive diagnosis?
• Name two rapid-type wet-mount stains that could readily demonstrate this organism?

CRYPTOCOCCOSIS

Cytologic evaluation. Low numbers of macrophages and neutrophils are observed in a moderately basophilic proteinaceous background and are consistent with mild to moderate pyogranulomatous inflammation. In addition, numerous round, pink, yeast-like organisms with a prominent clear capsule are observed individually and in clusters and are compatible with Cryptococcus. When this type of inflammation is present, underlying fungal infection should be one of your differential diagnoses. In this case of cryptococcosis, the fungal organisms are readily apparent and easily observed.

Foundation. Cryptococcus (C. neoformans) is one of the most common fungal organisms in cats. They are a saprophytic, round, capsulated, yeastlike fungus found worldwide. They range in size from 3.5 to 7 µm in diameter; capsule thickness ranges from 1 to 30 µm. These organisms replicate through narrow-based budding (Figure 3). Although the precise mechanism of transmission is unknown, inhalation of airborne organisms is believed to be most likely. Pigeon droppings are thought to be the main reservoir for the organism. The most common sites of involvement in cats include the nasal cavity (affected in more than 80% of cases), respiratory tract, central nervous system, skin, and eye. Nasal cavity involvement manifests as a polyp (as in this case) or swelling involving the bridge of the nose.1 Clinical signs depend on disease location. Diagnosis can be confirmed via cytologic examination, serologic testing, tissue biopsy, or fungal culture. Cytologic examination is the most rapid method of diagnosis. Organisms can be found in nasal exudate, draining lesions, tissue aspirates, cerebrospinal fluid, and aqueous or vitreous eye fluid. Organisms are often abundant and have a classic cytologic appearance (Figure 3). Many aggregates of pink, spherical, yeastlike organisms can be seen. The cells often have a clear-staining capsule with narrow-based buds on replicating cells. The aggregates range in size from 8 to 20 µm in diameter. 

DID YOU ANSWER. . .

• Pyogranulomatous inflammation.
• The appearance of the organism is consistent with Cryptococcus neoformans.
• Cryptococcosis with mild pyogranulomatous inflammation. Cryptococcus typically incites only a mild pyogranulomatous response in cats. If you diagnosed this correctly, you are a budding cytologist. The clinical pathologist at the diagnostic laboratory concurs with your findings-excellent job!
• If you indicated India ink and new methylene blue, you are an expert in the cytologic diagnosis of cryptococcosis.


CRYPTOCOCCUS • Kimberly J. Caruso

References
1. Infectious Diseases of the Dog and Cat. 2nd ed. Green CE., ed. Philadelphia, Pa: Mosby. 1998: 399-402

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