Cryptococcosis in Cats

Overview of Cryptococcosis in Cats

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.

Below is an overview of Cryptococcosis in Cats followed by detailed information on the diagnosis and treatment of this serious infection.

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

In affected cats, 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 of Cryptococcosis in Cats

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

Treatment of Cryptococcosis in Cats

Treatment for cryptococcosis may include:

Home Care and Prevention

Administer as directed any medications prescribed by your veterinarian and follow recommendations for dietary modification. Long term treatment up to 6 months or more may be required. Observe your pet’s general condition: Watch for worsening of symptoms and bring any changes to the attention of your veterinarian.

Some anti-fungal medications (e.g. ketoconazole, itraconazole) have the potential to cause liver damage. The animal should have periodic blood tests performed to evaluate for the presence of liver damage. These medications should be administered with food and they may cause vomiting or diarrhea.
Amphotericin B has the potential to cause kidney damage and must be given by intravenous infusion after being diluted in a 5 percent dextrose solution. The animal should have periodic blood tests performed to evaluate for the presence of kidney damage.

The possible sources of infection for affected animals should be evaluated because these areas represent potential sources of exposure and infection for human beings as well, especially children, immunosuppressed patients, and the elderly.

Restrict animals from areas that contain large amounts of pigeon droppings, especially shady, damp buildings. Areas where pigeons reside should be cleaned with hydrated lime diluted in water and sodium hydroxide solution.

In-depth Information on Feline Cryptococcosis

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 of Cryptococcosis in Cats

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

Diagnosis In-depth

Latex antigen titer is positively correlated with disease severity. Patients with disseminated skin or lymph node involvement have significantly higher titers than those that do not.

The presence of neurological signs, the species of the patient, concurrent viral disease in cats and the biotype of the isolate have no significant association with the latex agglutination titer.

Cats that die of active cryptococcosis despite treatment do not always have significantly higher titers than the ones that respond to treatment. Generally, the antigen titer declines by two- to four-fold per month during successful therapy. It has been recommended that antifungal therapy be continued until the latex agglutination test titer declines to less than one, or therapy be discontinued after a 32-fold or greater reduction in titer, with periodic monitoring of the serum antigen titer.

Treatment of serum samples with pronase substantially increased the sensitivity of the latex agglutination test.

Treatment In-depth

Treatments for Cryptococcosis in Cats may include:

Good prognosis is associated with decrease of serum antigen titers.

Follow-up Care for Cats with Cryptococcosis

Optimal treatment for your pet requires a combination of home and professional veterinary care. Treatment may be necessary for 6 months to one year. Follow-up may include frequent re-evaluation will be necessary until the pet’s condition stabilizes.

A decrease in the cryptococcal titer over time suggests effective treatment and a hopeful prognosis. Affected animals should be treated for one month after resolution of clinical signs and preferably until their cryptococcal titer becomes undetectable.

Treated animals should be monitored closely for drug toxicity. Periodic liver function tests should be performed in pets treated with ketoconazole or itraconazole and kidney function tests should be monitored in pets treated with amphotericin B.

Cats with cryptococcosis that also are positive for feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV) usually have a poor treatment outcome. Thus, determination of an affected cat’s FIV and FeLV status may allow the veterinarian to provide a more accurate prognosis for treatment.

The animal should be monitored closely for recurrence of symptoms after a decision has been made to stop treatment as a result of apparent recovery.

Therapy can be monitored repeating antigen titers. A decrease in the titers is indication of a positive response to the therapy. No vaccine is available. Contact with pigeon droppings should be avoided.