Cryptococcosis is an infectious disease caused by the fungus Cryptococcosis neoformans. The disease affects human beings and animals and is contracted by inhaling infectious spores. The excrement of birds, especially pigeons, is the main environmental reservoir for the spores, although birds rarely become infected with this organism due to the higher body temperature, which does not allow the growth of the organism. After the spores are inhaled, the organism spreads to other organs. Cryptococcus has a tendency to invade the nervous system.

Immunosuppressed humans and animals are at increased risk for developing cryptococcosis. Cryptococcosis has a worldwide distribution.

In affected dogs, non-specific symptoms of systemic illness are most common, such as weight loss and lethargy. Central nervous system problems may also occur such as head tilt, back-and-forth eye movements called nystagmus, paralysis of the facial nerve leading to inability to blink, incoordination, circling and seizures. Eye problems, such as hemorrhage in the retina and inflammatory disorders of the eye called chorioretinitis and anterior uveitis, also are common.

Contact with infected animals is not a concern because the yeast form of the organism grows in infected tissues and does not become aerosolized.

Diagnosis

Diagnostic tests are needed to recognize cryptococcosis and confirm the diagnosis. Tests may include:

A complete medical history and physical examination. The diagnosis of cryptococcosis is based on history, clinical symptoms, microscopic examination of exudates, serologic tests and biopsy if necessary.

Serology. Blood samples or samples of cerebrospinal fluid in animals with nervous system symptoms may be tested for antibodies. The most commonly used serology test is the latex agglutination test, designed to detect antigens from the capsule of the fungus. The test is very specific and sensitive. False negative results may occur in localized infections and false positive results may result from contamination of the specimen by talc from latex gloves worn during fluid collection.

Microscopic examination of exudate from cutaneous nodules or the nose. The organism also can be identified by microscopic examination of tissue biopsy specimens (histopathology). Special stains may be needed.