Cryptococcosis in Cats

What is Cryptococcosis in Cats?

Cryptococcosis is a type of fungal infection that occurs when a cat inhales spores from a type of fungus that grows in organic material such as soil, decaying wood, or bird guano (especially droppings from pigeons). Spores also can enter the skin through an open wound.

This infection is caused by either Cryptococcus neoformans or Cryptococcus gattii. Cryptococcosis is the most common fungal infection in cats and can spread throughout the body. Once infected, spores can spread to the respiratory tract (nasal cavity), central nervous system, eyes, and skin (mostly over the face and neck).

C. neoformans is found worldwide while C. gattii is native to Australia, New Zealand, Canada, the Pacific Northwest, and Central and South America.

Symptoms of Cryptococcosis in Cats

Because cats typically inhale the spores through their nose, upper respiratory symptoms are the most common:

• Sneezing

• Hard swelling over the bridge of the nose

• Polyps in the nasal passages, which may cause difficulty breathing

• Nasal discharge that may be blood-tinged, yellow, clear, or a combination of mucus and pus

Less often, the fungus may infect the lungs and cause coughing and rapid labored breathing. Skin lesions are also commonly seen on cats with this fungal disease, appearing as nodules or papules that can be fluid-filled or firm. Sometimes large ulcers that may drain fluid appear on the skin.

 A cat's central nervous system (CNS) may also be affected by the fungal organism, which may lead to the following symptoms:

• Depression

• Behavioral changes

• Walking in circles

• Seizures

• Muscular weakness

Dilated pupils, even when light is directed at the eyes (which may progress to blindness)

Causes of Cryptococcosis in Cats

Cryptococcosis is caused by spores inhaled from Cryptococcus fungus that can grow in soil, decaying wood, and bird guano (excrement). The spores usually enter the nasal cavity and can spread to the lungs by growing into the surrounding tissues.

The spores can then enter the bloodstream and invade other parts of the body, such as the skin, eyes, central nervous system, lymph nodes, urinary tract, spleen, GI tract, or pancreas.

When cryptococcosis spreads throughout a cat's body, this is referred to as a systemic fungal disease. Multiple organs can be harmed and symptoms can vary based on which organ or organs are affected.

How Veterinarians Diagnose Cryptococcosis in Cats

There are different ways to test for cryptococcosis:

• Cytology: The nostril is swapped to obtain a sample of the nasal discharge and examined under a microscope. Alternatively, a sample may be obtained by a fine needle aspirate (FNA) or from urine or cerebrospinal fluid (CSF).
   
• Latex agglutination test: This is an antigen test that detects if there is cryptococcal antigen in a cat's serum or CSF. False positive and false negative test results can occur with this test. Test results are usually available in 2-3 days.
   
• Fungal culture: This is a sample taken from urine, CSF, tissue or FNA. It may be grown on a culture plate to identify the fungus type. Test results can take about 2 weeks.
   
• Polymerase chain reaction (PCR) assay: This test detects the presence of a Cryptococcus species from a sample taken from the throat, nostril, trachea, or biopsy of a nasal mass. A rectal swab, fecal sample, whole blood, CSF, or a tissue sample can also be used for this test. It takes about 1-4 days to obtain the results.
   
• Histopathology: Biopsy samples from tissue, organ, or necropsy specimen can be sectioned and stained to scan for the fungus.

Treatment of Cryptococcosis in Cats

Once a cat is diagnosed with cryptococcosis, a veterinarian will prescribe anti-fungal medication. The type of medication that is prescribed will depend upon the severity of the infection.

• Mild to moderate infections may be treated with fluconazole. This medication is typically a 4-month treatment. Itraconazole may be prescribed instead, which usually requires about 9 months of treatment.
   
• In more severe cases that have central nervous system involvement or widespread infection, amphotericin B (AMB) along with flucytosine may be prescribed.

AMB is a very effective anti-fungal medication for treating cryptococcosis and it also helps to stimulate a cat's immune system to also fight the infection.

Cats undergoing treatment for cryptococcosis need to be rechecked by a veterinarian monthly. They also may need bloodwork and urine tests done periodically to monitor kidney or liver function, depending upon which treatment is prescribed.

Recovery and Management of Cryptococcosis in Cats

Recovery time varies based on the treatment prescribed. For mild to moderate infections, it can take 4 months with fluconazole or 9 months with itraconazole. For severe cases that involve the central nervous system, amphotericin B and flucytosine are prescribed, but these cases generally have a poor prognosis because the infection is widespread.

The length of treatment is based on cryptococcosis titers (concentrations of antigens). When the titer reaches zero, treatment is discontinued and then titers are done every 3-6 months to check for a relapse of infection. If the titer is unchanged after 2 months of treatment a different treatment plan is prescribed.

Cats generally have a good prognosis if they do not have central nervous system involvement. Between 15% and 20% of cats can have a relapse of infection and need to be treated again.

The best way to reduce risk for infection is to keep cats away from pigeon roosting areas and ideally keep them strictly indoors to reduce the risk for them to breathe in spores from Cryptococcus neoformans or Cryptococcus gattii.