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Blastomycosis is a relatively rare disease that is caused by inhalation of spores of the mold species Blastomyces dermatitidis (thanks to for this link).

In the US this is found in Ohio in the Mississippi river valleys, in northern Maryland, southern Pennsylvania, New York(central area), Texas, Florida, southeastern states, northern Midwest and southern Canada. However, there are other areas in the world, such as Africa and the Middle East where the spores are also endemic in the soil.

Conditions for multiplication of this pathogen are particularly good when soil is rich in excretions from animals and the soil is acidy and moist containing decaying organic material. Blastomycosis dermatitidis grows at room temperature. When the spores are inhaled and the immune system is weak, the heat increase from room temperature to body temperature (37°C or 98.6°F) will trigger conversion to large invasive yeast bugs.

The lungs immediately attempt to isolate them by surrounding the invading pathogen by mononuclear white blood cells that could in a healthy person stop the invasion. However, with the weakened immune system there is inflammatory granulation tissue that forms, the disease process enlarges and eventually fibrotic changes and lung scar tissue are formed. There can also be superinfection with bacteria or other fungal infections such as Candida albicans. Eventually there is an invasion into the circulatory system and disseminated blastomycosis results where blastomycosis foci are found in other organs such as kidneys, skin, vertebrae and other bones, prostatic and testicular tissue, thyroid gland, brain, bone marrow and other tissues. This condition is life threatening and often leads to death.


Usually blastomycosis (also called “Gilchrist’s Disease”) starts as a lung disease. It may not be recognized first and simply present as an infection with chills, a hacking cough and non specific chest pains. The patient may be very tired and have intermittent fevers and sweats. As the physician does a workup usually a chest x-ray is ordered, which will alert the physician that there is something different from the ordinary pneumonia going on.

Instead of an infiltrate in the periphery of the lung, the infiltrate of blastomycosis fans out from the center of the lung (called”hilum”) into the lung tissue. If the disease is not recognized and it progresses further, the patient gets symptoms from whatever organ is involved in the now disseminated blastomycosis. The most common symptoms are skin lesions (thanks to for this link) that can be more local or often also distributed all over the body surface, but with preference to exposed areas. They look like pimples, but can also look wart like. The lesions heal in the center leaving scarred skin behind, but advancing in the outside. The advancing border has a steep slope and there are often a number of mini abscesses along this border, which have a purplish red color.

Diagnostic tests

In the earlier form when only lung tissue is involved X-rays show characteristic changes suggestive of blastomycosis. However, bronchoscopy must be done by a respirologist to confirm the diagnosis. Samples can be taken for microscopic slides and with utilizing special staining techniques the lab can come up with the specific diagnosis. If this is not conclusive, then a blastomycosis cultures  (thanks to for this link) would confirm the diagnosis, which would also detect more minute quantities of the pathogen. Other diseases have to be excluded with appropriate tests such as cancer (bronchogenic carcinoma), other mycoses or tuberculosis.

 Blastomycosis (Petri Dish Culture)

Blastomycosis (Petri Dish Culture)


If blastomycosis is untreated, it would slowly and relentlessly infect the patient until the patient would succumb to the disease. Mild or moderate disease can be treated very successfully with the antifungal antibiotic itraconazole (brand name: Sporanox). Fluconazole (brand name: Diflucan) is less successful. Patients with severe life threatening infections are treated with intravenous amphotericin B (brand name: Fungizone) (Ref.1, p.1216).



1.The Merck Manual, 7th edition, by M. H. Beer s et al., Whitehouse Station, N.J., 1999. Chapter 158.

2.The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 113.

3. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 164.

4.David Heymann, MD, Editor: Control of Communicable Diseases Manual, 18th Edition, 2004, American Public Health Association.

Last modified: November 9, 2014

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.