Blastomycosis in Cats

Blastomycosis occurs when the spores come into contact with damp and warm conditions of your pet’s body such as lungs, eyes or nose, and can remain present in that area or spread to other areas of the body. Blastomycosis is more common in dogs than in cats, most likely due to the way dogs place their noses to the ground to smell and sniff, but can also occur in cats. Blastomycosis in cats requires veterinary care and can be life-threatening if not properly treated.

Blastomycosis is a non-contagious fungal infection caused by inhalation of or exposure to spores of the fungus Blastomyces dermatitidis. This fungus is found in damp, wet and warm soil regions, particular in swamp-like conditions or areas with large amounts of natural decaying matter. In the U.S., it is particularly common in areas located near water in Mississippi, Ohio, Missouri, and Tennessee. 

Symptoms of blastomycosis in your cat will vary depending on the exact location of infection. Symptoms of this condition may include:

• Pneumonia
• Breathing difficulties
• Skin disease, including masses or abscesses
• Ocular lesions
• Fever
• Lethargy
• Weight loss

Blastomycosis is caused by inhalation or exposure to spores of the fungus Blastomyces dermatitidis. Domestic cats can inhale these spores when allowed to roam outdoors near infected areas. Once the spores are inhaled, the fungus begins to grow and spread within your cat’s body, causing infection.

Diagnosis of blastomycosis in your cat will involve an initial physical examination by your veterinarian. At this initial exam, you should supply your vet with a thorough medical and physical history of your cat. You should inform your vet if your cat is allowed outdoors or if you have recently visited outdoors areas with your cat. You should also let your veterinarian known if any other animals in the household have recently been experiencing similar symptoms.

Next, your vet will order a full blood panel. This will involve a quick needle stick and withdrawal of a small amount of blood to be sent away for laboratory testing. Blood analysis will allow your vet to rule out conditions with similar symptoms. In some cases, the presence of antibodies against Blastomyces may be detected in the blood serum, however, this typically only occurs in advanced cases when your cat is already very sick.

Definitive diagnosis of blastomycosis will usually involve skin scrapings taken from open lesions or skin irritations. When viewed under a microscope, your vet will be able to identify the presence of the fungus in fluids from these areas. Your vet may also order x-rays which will help identify lung changes that are characteristic of the disease. In order for your vet to obtain the best quality images, your cat may need to be sedated or anesthetized for this procedure.

Treatment of blastomycosis will usually involve the administration of antifungal drugs. The most common drug of choice is called itraconazole. This medication is typically given orally, but in severe cases or instances which the cat will not eat, it may be administered via an IV. Itraconazole must be administered over a period of months in order to ensure complete elimination of the fungal infection. Your cat should be carefully monitored by your vet while they are on this drug, as severe reactions and liver damage may occur. Your vet will monitor your cat’s organ function with regular bloodwork during the treatment process.

If the fungus has infected the respiratory system, your veterinarian will also work to stabilize your cat’s condition and treat any severe symptoms. In cases of inflammation, antihistamines or steroids may be given to help reduce the body’s reaction to the infection and allow your cat to breathe. In many cases, your cat’s symptoms may get worse after medication treatment begins. This is due to the fact that the dying cells produce debris which can further inflame the respiratory passages. Treatment with steroids can also suppress your cat’s immune system, which may allow the fungus to grow or spread.

Your cat’s prognosis for recovery from blastomycosis will depend on the severity of symptoms. Unfortunately, there is a high rate of death in cats with severe respiratory infections even after treatment begins. In the case of skin ulcers and infection, the prognosis is somewhat better, but owners must be careful to follow medication dosing and care instructions from their vet as the infection can spread to other parts of the body.

Once cats have made it through the first two weeks of treatment, prognosis for recovery is good. In cats that have completed the full course of medication, there are generally no long-term side effects from blastomycosis. Treatment can last for several months and all medication should be given even after your cat has stopped showing symptoms given the fungus’ long life cycle.