[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Dimorphic fungi](https://durgical.com/en/microbiology/groups/dimorphic-fungi/) › Blastomyces dermatitidis

[Microbiology](https://durgical.com/en/microbiology/) · [Dimorphic fungi](https://durgical.com/en/microbiology/groups/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

## Key points

- Large yeast, thick wall, single broad-based bud
- Lung, warty skin and bone
- Rivers and lakes of North America
- Itraconazole; amphotericin B if severe

## 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 →](https://durgical.com/en/conditions/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:

- [Itraconazole](https://durgical.com/en/pharmacology/itraconazole/)
- [Amphotericin B](https://durgical.com/en/pharmacology/amphotericin-b/)

## Prevention

- No vaccine
- Suspect it in travellers to endemic areas with pneumonia that does not improve

## In Colombia

Not endemic in Colombia; it appears mainly in USMLE-style exams and in travellers to North America. In Colombia the main differential for a large yeast in tissue is Paracoccidioides.

## Memory aid

Blasto stands on a broad base: one bud with a wide neck, like a snowman with a thick neck.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/blastomyces-dermatitidis/)

## Related

- [Histoplasma capsulatum](https://durgical.com/en/microbiology/histoplasma-capsulatum/)
- [Paracoccidioides brasiliensis](https://durgical.com/en/microbiology/paracoccidioides-brasiliensis/)
- [Coccidioides immitis](https://durgical.com/en/microbiology/coccidioides-immitis/)

## Related conditions

- [Endemic mycoses: blastomycosis and coccidioidomycosis](https://durgical.com/en/conditions/endemic-mycoses-blastomycosis-and-coccidioidomycosis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Dimorphic fungi](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/blastomycosis/about/index.html) (CDC, 2026); [Clinical Overview of Blastomycosis](https://www.cdc.gov/blastomycosis/hcp/clinical-overview/index.html) (CDC, 2024); [Skin lesion of blastomycosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000865.htm) (MedlinePlus (NLM), 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/blastomyces-dermatitidis/