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Blastomycosis

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Last updated: January 2024

What is blastomycosis?

Blastomycosis is a rare fungal infection caused by breathing in microscopic particles (spores) of the fungus Blastomyces dermatitidis (B. dermatitidis).

Who gets blastomycosis?

Blastomycosis is not usually found in Australia. Humans as well as animals, such as dogs can develop blastomycosis.

Originally it was thought to be found only in North America, but cases have been reported from many countries in the world, including some parts of Africa and Madagascar. It occurs mostly in males who do outdoor activities and is more common in individuals with weakened immune systems.

What causes blastomycosis?

Blastomycosis is caused by breathing in microscopic particles(spores) of the fungus B. dermatitidis which is found in rotting wood, or moist soil with rotting wood and leaves.

What does blastomycosis look like?

The spores of B. dermatitidis can lodge in the lungs and cause an acute as well as a chronic pneumonia. Infected individuals may initially have flu-like symptoms. Later fever and shortness of breath may develop. Pulmonary symptoms can occur.

In 20-40% of cases the infection spreads to other parts of the body – the skin, bones, kidneys, reproductive organs, urinary tract, liver, spleen and central nervous system. 1

Common sites of cutaneous lesions of blastomycosis are face, neck, scalp, and upper limbs. These may look elevated, crusted, warty, plaque-like, or ulcer-like and can vary in size from a few millimetres to several centimetres. Early lesions can also appear as papules or pustules.  Chronic lesions appear as warty plaques. Rarely cutaneous lesions can be secondary to spread from an underlying bony lesion. Cutaneous lesions of blastomycosis can gradually increase in size if left untreated.

How is blastomycosis diagnosed?

The best way to diagnose the infection is to perform a fungal culture. A history of visiting an endemic area for blastomycosis and a prior history of blastomycosis of the lungs would give important clues to the diagnosis. It may also be diagnosed by examining a small sample of infected tissue under the microscope. An antigen test may detect the presence of the fungus in a urine or serum sample.

How is blastomycosis treated?

Some cases of blastomycosis improve spontaneously. Skin lesions of blastomycosis usually indicates systemic spread, as such it is best to treat the condition with systemic antifungals.

Treatment options will vary depending on the individual and their needs, and may include itraconazole, ketoconazole, fluconazole or amphotericin B.

Relapses may occur, particularly in those with weakened immune systems. Voriconazole and posaconazole can be considered in recalcitrant cases or where other drugs are not tolerated.

What is the likely outcome of blastomycosis?

Cutaneous lesions may cause scarring if treatment is delayed. Most individuals with mild lung infections recover without any specific treatment. 

Symptomatic patients recover fully with treatment.  Immunocompromised individuals need to be monitored to detect relapses of the disease.

  1. Tyring SK, Lupi Omar, Hengge UR. Eds Tropical Dermatology  2nd Ed.2017, Elsevier, Edinburgh

Prof Prasad KumarasingheJanuary 2024
Prof Prasad KumarasingheNovember 2014

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