Cryptococcosis is a common infectious disease caused by the yeast-like fungus Cryptococcus neoformans. This fungus is widespread in the environment and infection can occur in cats, dogs, humans and other animals.
Cats become infected when they inhale spores in the environment. It is the most common systemic fungal disease to affect cats.
The organism has worldwide in distribution but is most prevalent in temperate areas such as Australia and North America. It is found in areas contaminated with bird (especially pigeon) droppings. Pidgeons themselves don’t become affected due to their higher body temperature which doesn’t support growth of the fungus, it passes through them and out via the feces.
Immunocompromised cats such as those infected with FeLV or FIV are especially vulnerable to infections such as cryptococcosis due to their weakened immune status. Infected cats do not pose a risk to humans. Inhalation is the primary route of infection, less common modes of infection include inoculation or ingestion of the yeast cells.
Pathophysiology of cryptococcosis:
Dry yeast cells (known as basidiospores) are inhaled, they may remain localised in the nasal cavity and/or the lungs. In healthy animals, the fungus may remain isolated without causing the cat any problems. However, in immunocompromised cats (such as those with FIV or FeLV), the fungus may spread locally to the CNS or through the body via the bloodstream. Affected areas may include the eyes, brain, skin, central nervous system, and bones.
What are the symptoms of cryptococcosis in cats?
The incubation period is unknown. Symptoms vary depending on the organ systems involved. If the infection remains localised in the nose your cat may have no symptoms. If dissemination occurs, symptoms will vary according to the location of infection. The most common areas include the lungs, eyes and brain/CNS. The nasal form is the most common to occur in cat.
Your veterinarian will perform a complete physical examination and obtain a medical history from you. Diagnosis is based on identification of the organism. Cryptococcal infection should be considered in cats with chronic nasal discharge which doesn’t respond to antibiotics.
Tests your veterinarian may perform include:
Cytology of the nasal discharge or cerebrospinal fluid.
Histopathology (examination of biopsied tissues) of skin nodules, lymph nodes, nasal mucosa.
Latex agglutination test (LAT) to detect antigens from the capsule of the fungus in the blood. False negative tests may occasionally occur in cats with localised infection. False positives also occasionally occur.
If a negative antigen test occurs, a culture may be necessary.
Radiography of the nasal cavity may be useful.
Your veterinarian may also wish to perform CBC/biochemical profile/urinalysis, FIV and FeLV tests to gain an insight into the general health of your cat.
How is cryptococcosis treated in cats?
Itraconazole, fluconazole or ketoconazole are the drugs of choice for treating cryptococcosis. Treatment with anti-fungal drugs can take several months and up to a year. Cats with the CNS form may require lifelong medication. Liver and kidney function need to be regularly monitored while your cat is on these drugs. Side effects such as anorexia and vomiting may occur.
Amphotericin B for cats where the fungus has spread to the CNS or disseminated through the body. This drug is extremely potent and careful monitoring is necessary due to its potential side effects on the kidneys.
Surgical removal of the lesions in the nasal cavity.
Removing discharge from the nose and eyes with a damp cloth which will assist breathing.
Supportive care such as a feeding tube and IV fluids if necessary.
Your veterinarian will want to perform repeat antigen tests on the blood to monitor your cat’s response to treatment.
The prognosis is generally good for immunocompetent cats where the infection hasn’t disseminated, however, those with systemic disease and/or cats with FIV or FeLV don’t respond as well.
There is no vaccine for this disease, the only way to reduce your cat’s chances of infection are by limiting his exposure to potentially contaminated environments. The best way to do this is to keep him indoors or give him access to a cat enclosure.