Etiology and Agent Properties
The causative agents of chromoblastomycosis belong to the group of dematiaceous fungi. These are dimorphic microorganisms, which include several main species: Fonsecaea (compacta, pedrosoi), Phialophora verrucosa, Cladophialophora carrionii, Exophiala jeanselmei, Rhinocladiella aquaspersa, and Rhinosporidium seeberi.
The main feature of these fungi is the presence of melanin in the cell wall. It is melanin that imparts a characteristic brown-black hue to the fungal elements and their colonies.
The morphology of the agent depends on environmental conditions:
- In host tissues (in vivo): Fungi exist as clusters of round, dividing cells approximately 10 µm in diameter.
- In culture (in vitro): When inoculated onto Sabouraud agar, they form fluffy, dark brown colonies.
Epidemiology and Pathogenesis
The natural reservoir of infection includes soil, plants, and decaying wood. Transmission occurs via contact: the agent penetrates tissues through skin microtraumas. The most vulnerable zones (ports of entry) are the feet and shins.
The infection is prevalent mainly in regions with tropical and subtropical climates. It is important to note that an infected person poses no danger to others, as the disease is not contagious.
Pathogenesis is characterized by a protracted course (months or years). Specific changes develop in the affected area:
- Wart-like nodules form.
- Abscesses develop, followed by scarring.
- Satellite lesions form around the primary focus, giving the affected area a "cauliflower-like" appearance.
The host immune response is accompanied by the appearance of specific antibodies and the development of delayed-type hypersensitivity (DTH).
Microbiological Diagnostics
Laboratory diagnosis of chromoblastomycosis is based on detecting the causative agent and isolating it in pure culture.
- Direct Microscopy (Native Preparation)
The test material is pre-treated with a 10% KOH solution. The key diagnostic sign is the detection of so-called "sclerotic cells" (Medlar bodies). These are brown, round, septated cells. During differential diagnosis, specific exceptions are taken into account:
- Exophiala jeanselmei forms septate hyphae.
- Rhinosporidium seeberi (the causative agent of rhinosporidiosis) forms sporangia and sporangiospores.
- Culture Examination
Inoculation of pathological material is performed on Sabouraud agar. Incubation takes place at 20–25 °C. The agents grow slowly, with colony formation taking from 5 to 30 days. Morphologically, growth is represented by black septate mycelium with various types of conidia.
Management
Treatment of chromoblastomycosis requires a comprehensive approach.
- Pharmacotherapy: Systemic antifungal agents are used (itraconazole, flucytosine).
- Surgical treatment: Removal of affected tissues (excising nodules and abscesses) is indicated.
- Prevention: Specific prophylactic measures (vaccines) have not been developed to date.