Microbiology · Dimorphic fungi
Blastomyces dermatitidis !
- Fungus
- For completeness
A fungus of moist soils near North American rivers and lakes; it causes pneumonia and warty skin lesions, sometimes bone disease too.
Updated 2026-11-01
Also called: Blastomyces gilchristii, North American blastomycosis
At a glance
- Shape
- Large thick-walled yeast with a single bud joined by a broad base
- Family
- Ajellomycetaceae (Onygenales)
- Type
- Thermally dimorphic fungus: mold in soil, yeast in tissue
- Stain
- KOH on sputum or pus; PAS and silver (GMS) on biopsy
- Size
- Yeasts of about 8–15 µm
Morphology
- In tissue: a large yeast with a thick, double-contoured wall
- A single bud joined to the mother by a broad base
- In the environment: mold with small conidia
Transmission
- Inhaling conidia from moist soil with decaying wood and leaves
- Rarely direct skin inoculation
- Not spread from person to person
Reservoir: Moist soil and decaying plant matter near rivers and lakes
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Conversion to a large yeast at body temperature
- Surface adhesin (BAD-1) that aids binding and modulates the immune response
- Spread to skin, bone and the genitourinary tract
Diseases it causes
- Blastomycosis: acute or chronic pneumonia and disease spread to skin, bone, prostate and nervous system Endemic mycoses: blastomycosis and coccidioidomycosis →
Clinical picture
- Pneumonia that does not improve with antibiotics
- Warty or ulcerated skin lesions with raised borders, which can mimic cancer
- Osteomyelitis and prostatitis
- Can progress to acute respiratory distress syndrome
Diagnosis
- Antigen in urine or serum: fast (cross-reacts with Histoplasma)
- KOH or histopathology: large yeast with a broad-based bud
- Culture: reference standard, slow
- PCR
Treatment
Itraconazole for mild and moderate disease; amphotericin B for severe disease or nervous system involvement, followed by itraconazole.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- No vaccine
- Suspect it in travellers to endemic areas with pneumonia that does not improve
Test yourself
Think of the answer, then tap the question to see it.
What does Blastomyces look like in tissue?
A large thick-walled yeast with a single bud joined by a broad base.
Which organs does blastomycosis affect besides the lungs?
Mainly skin (warty lesions), bone, prostate and, less often, the nervous system.
How does the Blastomyces yeast differ from the Paracoccidioides yeast?
Blastomyces has a single broad-based bud; Paracoccidioides has many buds around the mother cell.
Related
Related conditions
← Back to the group: Dimorphic fungi
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Blastomycosis Basics (CDC, 2026); Clinical Overview of Blastomycosis (CDC, 2024); Skin lesion of blastomycosis: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024).
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Representative model, for educational purposes only.