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Microbiology · Molds and dermatophytes

Agents of chromoblastomycosis (Fonsecaea and other pigmented fungi) !

  • Fungus
  • For completeness

Dark fungi of soil and wood that enter through a wound, usually on a farmer's leg, and form slow-growing wart-like plaques.

Updated 2026-11-01

Also called: Fonsecaea pedrosoi, Cladophialophora carrionii, Phialophora verrucosa, chromomycosis

At a glance

Shape
In tissue, muriform bodies: round thick-walled cells divided by septa in several planes
Family
Herpotrichiellaceae (Chaetothyriales)
Type
Dematiaceous molds (pigmented with melanin)
Stain
KOH: copper-brown muriform bodies, visible without special stains
Size
Muriform bodies of about 5–12 µm

Morphology

  • Muriform (sclerotic) bodies: brown, thick-walled cells divided crosswise
  • In culture: dark colonies, olive green to black
  • Melanin in the wall gives them their colour

Transmission

  • Traumatic skin inoculation with splinters, thorns or plant material
  • More common in people who work barefoot or unprotected in the fields
  • Not spread from person to person

Reservoir: Soil, wood and plant debris in tropical areas

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Virulence factors

  • Melanin in the wall: resists killing by phagocytes
  • Muriform bodies persist in tissue and keep up chronic granulomatous inflammation
  • Slow growth with fibrosis

Diseases it causes

Clinical picture

  • Small painless first lesion on the leg or forearm
  • Wart-like or cauliflower plaques that grow over years
  • Black dots on the surface (good spots to sample)
  • Complications: lymphedema, bacterial infection and squamous cell carcinoma in old lesions

Diagnosis

  • Scraping of the black dots with KOH: brown muriform bodies
  • Biopsy: granulomas with muriform bodies
  • Culture and molecular methods for the species

Treatment

Long oral antifungal courses (itraconazole, terbinafine), often combined with physical methods (cryotherapy, heat) or surgery for small lesions. Large, old lesions respond poorly.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Footwear, gloves and protective clothing in farm work
  • Early care for a wart-like lesion that does not heal

Test yourself

Think of the answer, then tap the question to see it.

What is seen on KOH of a chromoblastomycosis lesion?

Muriform bodies: brown, thick-walled cells divided by septa in several planes.

How does a farmer acquire chromoblastomycosis?

By skin inoculation with splinters, thorns or contaminated plant material.

Which malignant complication can arise in old chromoblastomycosis lesions?

Squamous cell carcinoma.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Chromoblastomycosis (WHO, 2023); The global burden of chromoblastomycosis (PLOS Neglected Tropical Diseases, 2021).

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Representative model, for educational purposes only.