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Blastomycosis in Cats

Blastomycosis is a systemic infection caused by the dimorphic microfungus Blastomyces dermatitidis, which can be found in moist soil and areas of thick decaying matter such as river banks, lakes, swamps, forests, and woods. It is most prevalent in the mid-Atlantic, north-central and Ohio-Mississippi river valley areas. Fortunately, cats are more resistant to the disease than dogs and humans.  It has been suggested that immunocompromised cats may at greater risk of catching the disease.

The fungus comes in two forms:

  • Mycelial form - Found in the environment, this form is contagious.

  • Yeast form - Located within the infected host's body, this form is not contagious to others.

There is no breed or sex predilection, the disease is most commonly see in cats between 2 and 7 years of age.

How do cats become infected?

Cats become infected when they inhale the mycelial spores from infected soil. Spores enter the lungs where they multiply,  left untreated will go on to disseminate (spread) to other parts of the body (via the blood and lymphatic system) such as the bones, central nervous system, eyes, skin and lymphatic system.

Direct inoculation of the spores through the skin can occur in rare cases. Humans have become infected with blastomycosis from dog bites.

What are the symptoms of blastomycosis in cats?

The incubation period of blastomycosis is between 30 and 100 days. Not all infected cats will display symptoms.

When the fungus is inhaled, it initially causes primary disease in the lungs before disseminating to other parts of the body.

Many symptoms relate to generalised sickness and include:

Due to lung involvement, symptoms can be very similar to pneumonia and may include:

Other symptoms depend on the location of the infection but may include:

  • Ocular disease such as uveitis, retinal detachment, glaucoma can develop. Squinting, ocular pain, cloudy appearance, redness, squinting, sensitivity to light.

  • Draining skin lesions, the nose, face and claw beds are most commonly affected areas.

  • Lameness due to bone infection.

  • Blood in the urine (hematuria), difficult or painful urination (dysuria) if the urogenital system is involved.

  • Central nervous system disorders such as seizures, incoordination. This type of infection occurs most commonly in cats who are immunocompromised.

How is blastomycosis diagnosed?

Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you including if the cat has access to the outdoors.  He may listen to the lungs with a stethoscope (auscultation).

As symptoms are common in other diseases too, he may wish to perform some diagnostic tests to confirm blastomycosis. These may include cytologic or histologic identification of the blastomyces yeast forms in a biopsy from the lymph nodes. respiratory tract or fluid from a skin lesion.

He may also wish to check the overall condition of your cat and run further tests such as:

  • Serum biochemistry to determine the health of the internal organs.

  • Urinalysis to see if the urogenital tract has been involved.

  • X-Ray of the chest to evaluate the lungs.

How is blastomycosis treated?

Treatment consists of systemic antifungal medication.

Amphotericin B may initially be administered, this is given via injection. It can be toxic to the kidneys, so only small doses can be administered.

Itraconazole (5mg/per kilo/daily) is the drug of choice after amphotericin B has been finished. Your cat will need to be on anti-fungal medication for two months.  Other antifungals may include fluconazole and ketoconazole. These medications are cheaper but not quite as effective, therefore a longer course of medication may be required. Itraconazole and ketoconazole can cause liver problems so close veterinary monitoring will be necessary. Drug toxicity can occur with antifungal medications so close monitoring of your cat is necessary.

In some cases, surgical treatment will be necessary to treat your cat. This may include surgery to re-attach the retina or remove lesions from the lungs. 

Supportive care may also be necessary, this may include fluid therapy as well as nutritional support.

Prognosis is guarded and depends on the severity of the disease and the organs affected. Cases of blastomycosis with CNS involvement have the poorest prognosis.

Home care:

Administer medication as prescribed by your veterinarian.

Keep your cat indoors and exercise should be restricted. Your veterinarian may recommend cage rest.

Follow-up appointments with your veterinarian will be necessary to closely monitor the liver and kidney function while on medication.

Preventing blastomycosis in cats:

There is no vaccine for blastomycosis. The only way to prevent infection is to keep your cat indoors, especially if you live in endemic areas.

Keep up to date with your cat's vaccinations and make sure your cat is desexed to reduce his chances of contracting immune-suppressing diseases such as FeLV and FIV.

Also see:

Aspergillosis   Histoplasmosis   Ringworm