Blastomycosis – An Overview

Blastomycosis is an infection caused by inhaling a fungus called Blastomyces dermatitidis. This fungus is found in moist soils where there are decaying plants or wood. Blastomyces dermatitidis is found in the central and southeastern United States (the darkened area on the map to the right) and parts of Canada. Over the past 10 years, the rate of the disease in North America has increased.

To contract this disease, the fungus must enter the human body through the lungs. This happens, for example, through contact with moist soil, often where there are decaying leaves and vegetation. Then the fungus spreads to the rest of the body, especially the skin and bones.

It is a rare disease, occurring in only a few countries in the world, e.g., the United States, Israel, Canada, and Saudi Arabia. It tends to infect people with weakened immune systems more easily.

Symptoms vary and may occur 3 to 15 weeks after inhaling the fungus. You may develop mild symptoms and then recover without ever knowing you had the disease. Symptoms such as cough, fever, sputum/phlegm production, chest pain, weight loss, joint pain, shortness of breath, and body aches are common. However; the most common problem with blastomycosis is pneumonia. Because the symptoms of the disease are the same as many other problems (such as the common flu), your health care professional may not test you for the infection unless your symptoms do not go away or get worse despite taking antibiotics.

Blastomycosis may also be slow-growing and resemble a lung tumor, which can be mistaken for lung cancer. In some cases, infection can spread from the lungs to other organs, such as the skin, bones, joints, and central nervous system, and infect them. Skin problems include rashes, pustules, or nodules (small raised areas on the skin). Joint and bone problems include joint swelling or infected bone (osteomyelitis), which causes joint or bone pain. The infection in the central nervous system can cause meningitis, but this is unlikely in healthy people. If you have HIV/AIDS or you have had an organ transplant, you are more likely to get meningitis.

The doctor will look for symptoms on a physical examination of the patient. If he or she suspects an infection, various tests may be used to confirm the diagnosis. The most common tests are chest X-rays, saliva and urine tests. It is also advisable to perform a biopsy of an area of the skin showing symptoms.

The infection has an incidence between 1 and 2 cases per 100,000 people living in areas where the fungus occurs most frequently and is much less frequent outside these areas. The saprophytic mycelial phase of the fungus in the environment produces abundant conidiospores, which is the infective form of the disease. The ideal habitat for the presence of this mycelial form is moist soils with abundant organic matter (plant debris), shady, and with a pH<6, especially if the soil has been recently disturbed. These conditions are located on the banks of rivers and lakes with fallen trees. Very frequently associated with the construction of cabins or docks in these areas. The disease is very frequent in river and lake areas of the central and northeastern United States and Canada. The highest recorded incidence in the United States occurred in states such as Wisconsin, where from 1986 to 1995, there were 1.4 cases per 100,000 population.

In Canada, most cases of infection occur in northwestern Ontario, particularly around the Kenora area, because of its wet, acidic soils. Blastomycosis has a worldwide distribution, with some cases occasionally reported in Africa. Penetration is usually from inhalation and less frequently percutaneous. Once the infection has occurred, the process is not contagious. Humans are particularly susceptible, however, Retrievers and Pinschers, and cats are also very susceptible too. The presentation in horses is exceptional.

Not all patients with the disease need treatment. Occasionally, the symptoms of blastomycosis may disappear without treatment. Sick patients that spread to organs other than the lungs or whose symptoms do not improve will need treatment. The type of treatment is based on your symptoms and whether you are immunosuppressed. Treatment also varies depending on whether you have local symptoms (generally only affecting the lungs) or more systemic symptoms (affecting other organs in addition to the lungs). 

The drugs used to treat blastomycosis are antimicrobials (types of antibiotics also known as antifungal drugs) that are used to treat fungal infections. The type of antimicrobials you will receive will depend on the severity of your symptoms and the affected areas of your body. If you have a mild to moderate infection, the most common treatment is Itraconazole (solution or pill). In more severe cases, Amphotericin B (a drug administered by serum directly into the vein) is usually used. In both cases, treatment usually lasts 6 to 12 months.

There are side effects associated with treatments for this disease. Speak with a healthcare professional about any side effects you experience as a result of your particular treatment.

The best way to avoid the disease is not to travel to areas where blastomycosis occurs frequently. And when in these areas, avoid moving around in places with wet soils and decaying trees and leaves.