Last Updated on August 6, 2021 by Julia Wilson
Blastomycosis is a systemic infection caused by the dimorphic microfungus Blastomyces dermatitidis, which is present 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.
Immunocompromised cats may be at increased risk of catching this 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.
Cats become infected when they inhale the mycelial spores from contaminated 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.
The incubation period of blastomycosis is between 30 and 100 days. Many infected cats will be asymptomatic.
Inhalation of the fungus initially causes primary disease in the lungs before disseminating to other parts of the body.
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, on the nose, face and claw beds.
- 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, which occurs most often in immunocompromised cats.
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 evaluate involvement of the urogenital tract.
- X-Ray of the chest to evaluate the lungs.
Treatment consists of systemic antifungal medication and supportive care.
- Amphotericin B (Abelcet® or Fungizone®) – An antifungal agent administered by injection. This drug is not approved for use in cats by the Food and Drug Administration; however, it is regularly prescribed by veterinarians for off-label use.
- Itraconazole (5mg/per kilo/daily) – The drug of choice after amphotericin B has been completed. Your cat will need to be on anti-fungal medication for 60-90 days. 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 that the veterinarian will monitor the cat.
- Surgical treatment – This may include surgery to re-attach the retina or remove lesions from the lungs.
- Supportive care – Fluid therapy and 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.
- Administer medication as prescribed by your veterinarian.
- Restrict exercise and keep your cat indoors, your veterinarian may recommend cage rest.
- Follow-up appointments with your veterinarian will be necessary to monitor the liver and kidney function while on medication.
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.
Reduce your cat’s risks of developing immune-suppressing diseases such as FeLV and FIV with vaccinations.
Desex all cats to reduce the incidence of roaming.