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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Blastomycosis

Blastomycosis is a rare fungal infection caused by the fungus Blastomyces dermatitidis, which grows in wood and soil. It is a common infection among dogs, particularly in areas where it is prevalent.

The disease mainly affects the lungs with nearly 50% of patients often showing minimal or no symptoms. The infection may spread to other parts of the body. The skin is most commonly affected and is involved in about 20-40% of cases.

Causes and risk factors

Infection occurs by breathing in the spores that become airborne when contaminated soil or wood is disturbed. Humans and animals such as dogs, rats and cats may become infected. The disease is rarely transmitted from human-to-human or animal-to-human. Very rarely, infection via the skin may occur.

Blastomycosis can be found throughout the world but is most common in south-central and mid-western USA and Canada. The annual incidence in these areas is around 1-2 cases per 100,000 people. Although people of all ages and sex may become infected, people with weakened immune systems such as those with human immune deficiency virus infection (HIV) or organ transplant recipients are at greater risk of severe disease and infection spreading to other parts of the body.

Symptoms may not become apparent until 3-4 weeks after inhalation of the fungus. The mean time for symptoms to manifest is 45 days (range 21-106 days).

Clinical features

Patients usually present with respiratory symptoms that conform to one of the following specific patterns.

Symptom Pattern Features
Flu-like illness
  • Fever, chills, headache, non-productive cough
  • Symptoms may resolve within days without treatment
  • May go undiagnosed
Acute illness resembling bacterial pneumonia
  • High fever, chills, productive cough, chest pain
  • Sputum may be yellowish brown
Chronic illness resembling tuberculosis or lung cancer
  • Low grade fever, productive cough, night sweats, weight loss
  • Sputum may be yellowish brown or contain blood
Fast, progressive, severe symptoms resembling acute respiratory distress syndrome (ARDS)
  • High fever, shortness of breath, rapid breathing

Other symptoms that may occur include bone or joint pain, muscular stiffness and pain, prostatic involvement that may cause pain on urinating, and throat involvement causing hoarseness.

Cutaneous features of blastomycosis

Skin lesions are common on the face, neck and extremities as the infection spreads from the lungs to other parts of the body. One or many lesions may develop.

Diagnosis

Laboratory and radiological studies are performed to confirm the diagnosis of blastomycosis.

Patient history is also important in the diagnosis, particularly in areas where there may be a disease outbreak.

Treatment

Patients with blastomycosis confined to the lungs and who are not suffering from severe symptoms may not require any treatment. Usually symptoms are self-limiting and the infection clears spontaneously. Treatment should be used if infection in the lung worsens.

When the infection spreads and skin becomes involved, spontaneous resolution does not occur and treatment is necessary.

Patients with limited skin lesions and relatively mild lung involvement usually recover completely. Untreated or more severe disease can lead to severe scarring and disfigurement or death.

Related information

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Author: Vanessa Ngan, staff writer

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If you have any concerns with your skin or its treatment, see a dermatologist for advice.