Blastomycosis — also known as blasto, North American blastomycosis, or Gilchrist disease — is a rare infection caused by breathing in a fungus called blastomyces. It usually affects the lungs but can spread to other parts of your body, such as your skin, joints, and bones.
The fungus that causes blastomycosis lives outdoors in soil, leaves, and rotting wood, especially in areas near water. It is a mold that creates spores. If you disturb the ground where blastomyces is growing, it can release spores into the air. You might breathe these in without knowing it, as they’re too small to see. Pneumonia-like symptoms usually appear later if you have an infection.
Blastomyces, while rare, is most commonly found in North America, especially in the Midwestern states, with hotspots in Wisconsin and Minnesota. It’s also found in South Central and Southeastern U.S., as well as in Southeastern Canada. Blastomyces has also been reported in India and parts of the Middle East and Africa.
Since not every state or province reports blastomycosis, it’s hard to get a clear picture of the exact numbers, says Ilan Schwartz, MD, associate professor of medicine in the Division of Infectious Diseases at Duke University, who has studied blastomycosis. “The other part of it is that only a very small proportion of cases are ever microbiologically diagnosed, so there's a huge undercounting,” he says.
Fortunately, most people who live in areas where the fungus grows aren’t likely to get blastomycosis, Schwartz says.
Blastomycosis Symptoms
About half of the people who breathe in blastomyces spores will have symptoms. Symptoms may show up anywhere from three days to three months after exposure. Some cases get better without treatment.
Symptoms of blastomycosis are similar to those of pneumonia and include:
- Coughing (sometimes with 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
Blastomycosis isn’t contagious, meaning you can’t get it from another person. There have been a few rare cases of people getting a skin infection after being bitten by an animal with the fungus, but this is uncommon. Simply having contact with an infected animal isn’t enough to get blastomycosis.
How long your symptoms last can vary depending on your health. Most people have to take antifungal medications for at least six months.
Blastomycosis sores
The infection can spread to your skin or other parts of your body. If that happens, you may notice bumps or sores. Schwartz says these tend to appear as ulcers or warts. “They’re usually crusty, raised lesions, or a combination of those two. Those might be present for many months in some individuals,” he says.
Sores may also:
- Appear as large, open wounds or smaller clusters of bumps
- Be gray or violet in color
- Form in your mouth or nose
- Bleed easily
Blastomycosis Causes
Blastomycosis is caused by a fungus called blastomyces. Because it has only been detected in the environment a few times, researchers aren’t sure what conditions help it grow, Schwartz says. But it tends to live in moist soil and rotting wood. If you garden, dig up, or move around soil that has blastomyces fungus, you might stir up the spores and breathe them in. In about 50% of people, this will lead to a blastomycosis infection.
How is blastomycosis transmitted?
If you breathe in blastomycesspores, the fungus can grow in your lungs and cause an infection. It’s possible for the infection to spread through your bloodstream to other parts of your body.
“Very few people who are exposed to blastomyces actually develop an infection, based on the number of cases that are diagnosed and reported each year in areas where we think the fungus occurs,” says Schwartz. “There are many people that live in areas where it’s known to be endemic, but there’s still a small number of cases.”
Animals get blastomycosis the same way humans do — by inhaling the spores. Cats are less likely to get it than dogs.
Blastomycosis Risk Factors
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:
- Are taking a medicine that affects your immune system
- Have received an organ donation
- Have HIV/AIDS
Blastomycosis Diagnosis
If you think you’ve been exposed to blastomyces fungus or an infected animal, see your doctor or health care provider. They’ll ask where you may have come into contact with 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 your results.
The symptoms of blastomycosis often look like those of other illnesses, including bacterial pneumonia. An early and accurate diagnosis is important to help you get the right treatment quickly.
Because blastomycosis is so uncommon, some doctors may not know enough about fungal lung infections to diagnose them accurately, especially if they don’t often see cases in their region. In areas where blastomyces isn’t common, doctors might not think to test for it, so they may misdiagnose fungal infections as bacterial ones. In those cases, you may be prescribed antibiotics instead of an antifungal medication. Antibiotics won’t heal a blastomycosis infection, which may cause it to get worse or spread before you get the right diagnosis.
When you take antibiotics your body doesn’t need, you also increase your chances of antimicrobial resistance. This means that drugs may not work as well if you really need them in the future.
Blastomycosis Treatment
If your immune system works well, it’s relatively simple to treat blastomycosis. Your doctor will give you a prescription antifungal medication like itraconazole, which you’ll take for 6-12 months.
If the infection is severe or has spread to other parts of your body, your health care provider may start with a stronger medication called amphotericin B for a few weeks. After that, you’ll likely switch to itraconazole for anywhere from six months to a year or more.
If the infection is very mild, limited to your lungs, and already getting better by the time you are diagnosed, you may not need treatment. But in most cases, doctors will recommend medication to make sure the infection clears up.
Blastomycosis Complications
If you have a severe case of blastomycosis, it could lead to acute respiratory distress syndrome (ARDS). ARDS is a condition that causes fluid to build up in your lungs, making it hard to breathe. When your lungs can’t move enough oxygen to the rest of your body, including your brain, heart, and kidneys, these organs may stop working properly. ARDS can be life-threatening.
Other complications that can arise from blastomycosis include:
- Fungus spreading to other parts of your body, including your skin or bones
- Scarring from skin sores
- A relapse of the infection
- Side effects from medications used to treat it
Blastomycosis Prognosis
Because of limited testing and reporting, data on blastomycosis cases in the U.S. is incomplete. It’s estimated that there are fewer than 2 cases per 100,000 people.
Only half of the people infected with blastomycosis have symptoms, and these cases tend to clear up on their own. If you do have symptoms but have a healthy immune system, you’re unlikely to have complications as long as you get proper treatment.
If left untreated, the infection can be fatal. Among those hospitalized with blastomycosis, an estimated 8%-10% of people die.
Blastomycosis Health Disparities
Research shows health disparities in who gets blastomycosis and how it affects different groups of people.
There’s limited research on this fungal infection, but most studies have been done on White people. Some evidence does suggest that it affects certain races differently. For example, studies show that Black people and Native Americans have a higher rate of complications and death from blastomycosis than White people. The reasons for this aren’t completely clear, but health inequalities caused by social differences, such as living conditions, income, occupation, and access to care, could play a role.
Blastomycosis Prevention
You can’t prevent blastomycosis. Although you can avoid exposure to soil in areas that may have the fungus, 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.
Takeaways
Blastomycosis is a rare but potentially serious fungal infection caused by inhaling spores from the fungus called blastomyces. This fungus lives in moist soil and rotting wood in some regions of the U.S. and Canada. While some people recover without treatment, many need to take antifungal medication for several months. Symptoms can resemble those of pneumonia and are often misdiagnosed, especially in areas where the fungus isn’t common. Early diagnosis is important, and most people make a full recovery with proper treatment.
Blastomycosis FAQs
What kills blastomycosis?
Antifungal medications such as amphotericin B or itraconazole can kill the fungus that causes blastomycosis.
Can a dog survive blastomycosis?
With proper treatment, many dogs can survive blastomycosis. The recovery rate is estimated to be about 50%-75%.
Can blastomycosis cause death?
If left untreated, a blastomycosis infection can cause death, especially in people with weakened immune systems.
What is the largest outbreak of blastomycosis?
The largest known outbreak of blastomycosis occurred among paper mill workers in Michigan between 2022 and 2023. A total of 162 cases were reported.
