What Is Blastomycosis?

Medically Reviewed by Melinda Ratini, MS, DO on April 12, 2023
5 min read

Blastomycosis is a rare infection caused by a fungus called BlastomycesMost of the time it infects the lungs. The infection is otherwise known as blasto, North American blastomycosis, or Gilchrist disease.

The fungus that causes blastomycosis lives outdoors in dirt, leaves, and wood. It is a mold that creates spores. 

Blastomyces is common in the Midwestern, South-Central, and Southeastern U.S. It’s very common in Wisconsin. The fungus also lives in Canada. Blastomyces has been reported in India and Africa, too.

Experts say climate change causes fungi like Blastomyces to spread outside the areas they usually live. This can lead to a rise in infections.

About 50% of people who breathe in Blastomyces spores will have symptoms. They can start as soon as 3 days after exposure or show up within 3 months of exposure. Some cases get better without treatment.

Symptoms of blastomycosis include:

  • Coughing (or coughing up blood)
  • Fever
  • Shortness of breath
  • Chest or back pain
  • Muscle aches or joint pain
  • Night sweats
  • Loss of appetite or weight loss
  • Feeling tired
  • Skin sores

When the infection spreads, you may notice sores on your body. The sores:

  • Usually are painless
  • May look like an ulcer or wart
  • Can be gray or violet colored
  • Can occur in your mouth or nose
  • May bleed

Blastomycosis isn’t contagious. You can’t get it from another person. You also can’t get it from animals, except in a couple of rare cases when a human got a skin infection after being bitten by an animal who was sick with the fungus. 

How long symptoms last varies a lot depending on your health. Most people have to take antifungal medications for at least 6 months. 

You may be exposed to Blastomyces spores if you’re moving soil around, through activities like gardening or digging in the dirt. 

Once you inhale the spores, it starts an infection in your lungs. In some cases, the fungus directly infects an open skin wound and affects only that part of your body.

Animals get blastomycosis the same way humans do -- by breathing in the spores or exposing an open wound to spores. Cats are less likely to get it than dogs.

Anyone can get blastomycosis if they’re in an area where the fungus grows.

You may be more at risk if you:

  • Work outside (in a job like construction)
  • Spend time in the dirt
  • Work in a lab
  • Get bitten by an infected dog or are stuck with a needle that’s been in an infected dog, but this is very rare and infects the skin, not the lungs 

You’re at risk for severe infection if you have a weakened immune system. This can be the case if you’re taking a medicine that affects your immune system, you have received an organ donation, or you have HIV/AIDS.

If you suspect you’ve been exposed to the fungus or an infected animal, see your doctor or health care provider. They’ll ask about where you may have gotten it and do a physical exam. 

Your health care professional may run any of the following tests to see if you have blastomycosis:

  • Chest x-ray
  • Chest CT scan
  • Skin or tissue biopsy or culture
  • Culture of your sputum (chest congestion)
  • Urine test
  • Blood test

It can take a few days or weeks to get results.

Early detection is important. An accurate diagnosis is also key. Blastomycosis symptoms are similar to bacterial pneumonia, for example. This means you could be misdiagnosed and not get the right treatment quickly. 

Experts say doctors may not have enough knowledge about fungal lung infections like blastomycosis. They may not expect them in their geographic region because it may not have been a hot spot for blastomycosis in the past.

It’s common for health care professionals to misdiagnose fungal infections as bacterial infections. That means you may get antibiotics instead of an antifungal medication. The antibiotics won’t heal the infection, and by the time you see that you haven’t responded to them, your fungal infection could be worse or spread. 

When you get antibiotics your body doesn’t need, that can contribute to antimicrobial resistance. This means that drugs may not be able to kill bacteria when you need them to in the future.

It’s relatively simple to treat blastomycosis if you have a properly functioning immune system. Your doctor will give you a prescription antifungal medication like itraconazole. You may be on it for 6 months to a year.

If you have a severe case that’s spread to other parts of your body, your health care professional may put you on amphotericin B for a few weeks. You’ll probably then take itraconazole anywhere from 6 months to a year or more.

If you have a very mild infection that is only in your lungs and it is already getting better by the time you are diagnosed, you may not need treatment. But most of the time, you will receive treatment.

If you have a severe case, you can develop:

  • Scarring from the skin sores
  • A relapse of the infection
  • Side effects from medications used to treat it

Your prognosis, or outlook, is good if you have a healthy immune system. You’re not likely to have complications. 

If you don’t treat blastomycosis, you could die from it. There were 4,441 cases between 1987 and 2018 in five states (Arkansas, Louisiana, Michigan, Minnesota, and Wisconsin). Of the people infected, 8% died.

Some research shows health disparities in terms of who gets blastomycosis and how it shows up.

Research on this fungal infection is mostly based on White people. Some evidence shows clinical differences based on race. In fact, if you’re Black, there’s a higher rate of infection, higher chance that it will spread throughout your body, and higher chance of death. There are also higher rates of it in Canada’s indigenous people, American Indians, and Asian people compared to White people.

You can’t prevent blastomycosis. You can avoid exposure to soil in areas that may have it, but you can still get it if the spores are in the air. There’s no way to test your soil to see if the fungus is in there.