What is Blastomycosis and how does it infect dogs and cats?

Blastomycosis is a serious and sometimes life-threatening fungal infection caused by Blastomyces dermatitidis. Dogs and, rarely, people and cats become infected when they inhale the fungal spores into their lungs, usually when digging in the soil. Once in the lungs, the fungal spores begin to grow and reproduce, and spread throughout the body, often infecting other organs. While not very common, infection can happen by contamination of an open wound on the skin.

The fungal organism has been difficult to find in the environment, however, both dogs and people seem to become infected in geographical pockets. Blastomycosis is typically found in warm, moist areas along the Ohio, Missouri, Tennessee, St. Lawrence, and Mississippi River valleys and is very common in the Southeastern United States. The disease has been found in the Middle Atlantic States, Quebec, Ontario, Manitoba, and southern Great Lakes.

Blastomycosis is seen infrequently in cats and people and more frequently in dogs. Experts estimate that dogs are about ten times more likely to get blastomycosis than people and about 100 times more likely than cats.

How does blastomycosis infect and spread throughout the body?

The time between exposure to the fungal spores and developing signs and symptoms is approximately 5 to 12 weeks. The infection usually begins in the lungs and spreads to the rest of the body.

About 50% of patients with blastomycosis will develop eye infections. It also affects skin and lymph nodes. Less often, the fungus infects bone, brain, or reproductive organs. In rare cases, patients will only have a local skin infection which happens if the patient has an open skin wound that gets exposed to the fungus in the soil.

While rare, it has been reported that people exposed to discharge from a dog’s blastomycosis-infected wounds have become infected themselves. Practice good hygiene, wear gloves and wash hands thoroughly when treating any open wounds on a dog’s skin.

Symptoms of Blastomycosis in Dogs

Signs of infection depend on what organ or part of the body is infected. Usually, dogs experience coughing, difficulty breathing, fever, and weakness or decreased activity such as exercise intolerance. Owners may notice inflammation of the eye(s) or that their dog has suddenly gone blind before noting any respiratory symptoms.

Blastomycosis can show up as a skin infection, sometimes with discharge, without any history of trauma to the skin.

Diagnosing Blastomycosis in Dogs

Your vet will perform a complete physical exam and ask you several questions which often point in the direction of possible fungal disease. Diagnosing blastomycosis includes blood and urine tests and x-rays to evaluate the lungs and other areas of the body that may be affected. Tissue samples of affected organs, usually by fine needle aspirate, are examined microscopically. If fungal organisms are found, the patient is diagnosed positive for blastomycosis.

Dogs diagnosed with blastomycosis are considered to have a generalized infection, meaning that the fungus has spread throughout the body.

Veterinarians recommend getting a sample from affected lung lesions, as treatable fungal lesions can look a lot like less-treatable cancer lesions on x-rays.

Available Treatments for Blastomycosis

Most dogs diagnosed with blastomycosis can be treated with prescription oral anti-fungal medication prescribed by their vet. Severely ill patients need to be hospitalized and receive intravenous medication which can have serious side effects and be quite costly.

Fungal infections often need to be treated for at least 4-6 months. It’s important not to stop the prescribed medications until your vet determines that your pet no longer needs treatment.

Long-Term Follow-Up

Dogs diagnosed with blastomycosis need to be closely monitored by their primary vet or by an internal medicine specialist while they are on the prescription anti-fungal medication and for a few months after finishing their medication. The vet will want to monitor how the patient is doing, response to treatment, and any side effects from the medication. This often requires urine testing to make sure that the dog has cleared the infection. Several negative tests a few months apart are recommended. Stopping medications too early can cause a relapse of the infection.

Preventing Blastomycosis in Dogs

Blastomycosis fungal spores live everywhere and cannot be eliminated from the environment. Watch your pet closely for any symptoms listed above, especially if you live in any of the warm, moist areas such as the Southeastern United States.

Can I get blastomycosis from my dog?

If your dog has been diagnosed with blastomycosis it may be that the Blastomyces organism lives near your home. You should talk to your family doctor about your pet’s illness so that they are aware of the possible risk of fungal spore exposure to you and your family.

If anyone in your family falls into one of the following categories, we recommend that you consult with your family physician regarding the risk of exposure to a pet diagnosed with blastomycosis:

• Infants or small children

• Organ transplant patients

• HIV/AIDS patients

• Elderly family members

• Anyone with a known immune system disease

When to Call the Vet

If you live in or travel to any of the areas listed above, stay alert for the following in your dog, especially if they like to dig in the dirt: coughing, difficulty breathing, eye changes, skin infections, enlarged testicles, fever, and a decrease or no appetite. If you notice any of these symptoms, schedule an appointment with your primary vet.

Read more:

Aspergillosis in Dogs and Cats

Cryptococcosis in Dogs and Cats

Histoplasmosis in Dogs and Cats

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