Cryptococcosis is a systemic fungal disease caused by Cryptococcus neoformans. Cryptococcus is a yeast-like fungus found most often in association with pigeon droppings. Cryptococcus does not cause disease in pigeons due to the high body temperature of these birds (107.6 degrees Fahrenheit or 42 degrees Celsius), which inhibits growth of the organism. Optimal growth occurs at 98.6 degrees F (37 C), which is the average temperature of mammals. It has worldwide distribution. It is the most common systemic mycosis in cats.

Cryptococcus has a thick capsule surrounding it, which contributes to its virulence and resistance to treatment. Infection occurs after inhalation of the organism, when cryptococcus produces a thick capsule that interferes with the ability of the immune system to eliminate it.

Animals that are compromised immunologically, such as by feline immunodeficiency virus, feline leukemia virus, corticosteroid therapy or malnutrition are most susceptible.

Spreading of infection depends on the host's immunity however not all affected animals have concurrent immunosuppressive disease to justify the development of cryptococcosis. Cell-mediated immunity is vital to recover from Cryptococcosis. More specifically, it seems that T helper type 1 cells (the ones producing interleukin-12 and gamma interferon) are the ones involved in the defense mechanisms against this type of infection.

Clinical Symptoms

Respiratory disease is present in most cases (70 percent). The nasal cavity is affected in 80 percent of cats. Sneezing and nasal discharge are common clinical symptoms.

Involvement of the nasopharynx is common. Symptoms such as snoring and breathing difficulty are seen.

Superficial skin nodules are found in 40 percent of animals. They include papules, nodules and draining tracts. Organisms are frequently detected in the draining material.

Neurological signs are variable depending on the location of the infection. They are present in 15 percent of cases and include ataxia, seizures, depression, circling, head-pressing, head tilt, nystagmus, facial paralysis, and blindness.

Ocular signs are present in 15 percent of cases and include dilated, unresponsive pupils, infection of the retina, retinal hemorrhage and inflammation of the front chamber of the eye are not uncommon.

Other diseases of the nasal cavity and nervous system may produce similar signs and must be eliminated as diagnostic possibilities:

Nasal cavity tumors

Foreign bodies in the nasal cavity

Other fungal infections (aspergillosis)

Tooth root abscess

Chronic bacterial sinusitis

Nervous system diseases

Other infectious diseases such as distemper and toxoplasmosis

Cancer of the nervous system like lymphosarcoma

Granulomatous meningoencephalitis

Epilepsy

Certain metabolic diseases like hepatic encephalopathy

Drug or chemical toxicity