What to Know About Blastomycosis in Dogs

Medically Reviewed by Amy Flowers, DVM on December 12, 2021
4 min read

Blastomycosis is a fungal infection that happens in some areas of the U.S. Dogs are more likely to get it than other animals.  

Blastomycosis is an infection caused by the fungus Blastomyces dermatitidis. Both humans and dogs can get blastomycosis by breathing in fungi spores from the dirt.

Blastomyces live in wet soil and decomposing wood and leaves. In the U.S., it's mostly found around the Great Lakes, Saint Lawrence River, Ohio Valley, and Mississippi River Valley. The fungi are also found in Canada, Africa, and India.

When the soil is disturbed, the spores are spread in the air. Both you and your dog can breathe them into your lungs. If your dog likes to dig in the dirt or swim near areas that have fungi, they are also more likely to breathe in the fungi.

Most people don’t get sick from breathing in the spores, but dogs are more likely to get blastomycosis than other animals. Blastomycosis can’t pass between you and your dog, though.

If your dog has a weak immune system, gets a severe infection, or the infection spreads to other parts of the body, blastomycosis can make them very sick. 

Blastomycosis symptoms in dogs are similar to symptoms in people. An infection looks a lot like other lung conditions and includes symptoms like:

Blastomycosis can also cause growths in the lungs and a cough that sounds harsh and dry. About 85 percent of dogs with blastomycosis have a lung infection, but it can spread throughout the body and affect the brain, eyes, lymph nodes, bones, and skin. 

When it spreads, it can cause other symptoms like:

  • Glaucoma 
  • Blindness
  • Detached retina
  • Skin abscesses
  • Nail infections
  • Joint and muscle pain
  • Bone infection
  • Trouble exercising

Symptoms can vary in severity and depend on how many parts of the body are affected.  

Your vet will do a physical examination and ask about your dog’s history. If your dog has sores or cysts, a cough, and breathing problems, your vet might consider the fungus. To confirm, they will do some blastomycosis testing. 

Your vet might order a blood test, or swab a skin sore to check for the fungus. They might also do a chest X-ray to look for lung infections. Blastomycosis causes growths and swollen lymph nodes in the lungs. Some urine tests can also help find fungus cells. 

Blastomycosis is treated with different antifungal medications, including itraconazole, ketoconazole, fluconazole, amphotericin B, and some combination therapies. Your dog will take the medicine for at least 2 months and might stay on it longer until symptoms are gone and tests are clear. Itraconazole has fewer side effects than other medications, so it’s generally well-tolerated.

Sometimes sores and infected parts of the skin might need to be removed with surgery, but this is rare. 

If your dog has a severe infection, your vet might combine itraconazole with Amphotericin B, another antifungal medication. If the dog’s lungs are full of fungi, they will be closely monitored. Once the medication starts to work, the dog’s immune system can react and cause serious lung problems. 

The outlook is good for dogs with mild blastomycosis infections who get treatment. More than 70 percent of dogs get better. Blastomycosis can come back, but most dogs can have the medication again. Without treatment, blastomycosis is life-threatening for your dog. 

Symptoms and infections can vary in severity. Some infections are worse than others and may have a poor outlook. Dogs with weak immune systems might especially have trouble in the first few days of treatment and will need to be closely monitored. 

There is no vaccine to prevent blastomycosis. Since the fungi are in wet soil and water, some dogs are more likely to be exposed. Sporting and hunting dogs who are in the water and wet areas are more at risk. 

If you live or visit areas where the fungus is commonly found, your dog can also be exposed:

  • From freshly landscaped dirt
  • While camping
  • Hiking in wet areas
  • While swimming

But any activity that turns up the dirt can be at risk, so it’s likely not possible to fully avoid the fungus. You can avoid these areas to try and prevent infection, especially if your dog has a weak immune system or other serious disease. If you’re concerned about your dog’s health, talk to your vet