Ecology and mechanism of infection
The environmental acts as the natural reservoir for microorganisms causing subcutaneous mycoses. These pathogenic and opportunistic fungi freely inhabit the soil and the surface of wood. Furthermore, their favored breeding ground consists of decaying and rotting plants, which determines the specific nature of human contact with the pathogen.
Infection occurs exclusively via a traumatic route. For the fungus to penetrate the body, a portal of entry in the form of skin microtraumas is required. The infection is introduced into the tissues during accidental skin damage by splinters, plant thorns, or when any other foreign bodies contaminated with fungal elements enter a wound. Without a breach in the integrity of the epidermis, the development of a subcutaneous mycosis is impossible.
Pathogenesis features
A key feature of subcutaneous mycoses that distinguishes them from superficial dermatophytoses is the considerable depth of tissue involvement. The pathological process is never limited solely to the epidermis.
Fungal invasion relentlessly spreads inward, sequentially capturing the deep layers of the dermis and subcutaneous adipose tissue. In the absence of timely cessation of the process, the infection penetrates even deeper, involving the underlying structures of the musculoskeletal system—muscles and fascia—into the inflammation. Such deep damage determines the severity of the clinical course and the complexity of treating this group of diseases.
Sporotrichosis and chromoblastomycosis
In medical microbiology, several main nosological forms of subcutaneous mycoses are distinguished, each associated with specific groups of microorganisms.
- Sporotrichosis. It is a chronic infectious disease. Its primary and most well-known causative agent is the fungus Sporothrix schenckii.
- Chromoblastomycosis. This form of pathology is caused by specific pigmented fungi. The main representatives of pathogens provoking the development of chromoblastomycosis include microorganisms of the genera Phialophora (specifically the subspecies Fonsecaea), Cladophialophora, Exophiala, as well as Rhinosporidium.
Mycetoma and phaeohyphomycosis
In addition to sporotrichosis and chromoblastomycosis, two more nosological forms of subcutaneous mycoses play a significant clinical role:
- Eumycetoma (Madura foot). This is a classic polyetiological disease. Polyetiology means that the clinical picture of mycetoma can be provoked not by a single specific species, but by a whole group of diverse fungi. Among the most frequent causative agents are representatives of the genera Pseudallescheria, Madurella, Acremonium, and Leptosphaeria.
- Phaeohyphomycosis. This pathology is caused by so-called dematiaceous, i.e., dark-colored fungi. This extensive group of pathogens includes fungi belonging to the genera Exophiala, Phialophora, Wangiella, Bipolaris, Alternaria, and Cladosporium.
Briefly: answers to topical questions
What clinical symptoms and skin manifestations are characteristic of sporotrichosis?
Sporotrichosis is characterized by the development of lymphangitic (lymphocutaneous) and visceral forms of the disease. Skin manifestations begin with a primary lesion at the site of trauma:
- Primary lesion — formation of painless and indurated nodules, abscesses, or an irregularly shaped ulcer.
- Secondary eruptions — formation of nodules along the course of proximal lymphatic vessels with their subsequent ulceration.
Upon dissemination of the pathogen, visceral sporotrichosis develops with involvement of the lungs (including primary pulmonary sporotrichosis), the skeletal system, abdominal organs, and the brain.
What laboratory diagnostic methods are used to identify the causative agents of subcutaneous mycoses?
To identify the causative agents of subcutaneous mycoses, microscopic, cultural, serological, biological, and histological methods are used.
- Microscopy — examination of smears, biopsy specimens, or pus with 10% KOH to detect hyphae, chlamydospores, grains, "sclerotia" (Medlar bodies), or "asteroid bodies".
- Cultural method — inoculation on Sabouraud agar to isolate a pure culture and demonstrate thermal dimorphism.
- Histological method — biopsy with staining (PAS reaction, Grocott's methenamine silver stain) to visualize hyphae in the dermis.
- Serology — detection of antibodies (agglutination test, precipitation test, ELISA).
- Biological test — infection of laboratory animals (guinea pigs).
What antifungal drugs are used to treat chromoblastomycosis and mycetoma?
For the medical treatment of chromoblastomycosis, antifungal drugs such as itraconazole and 5-flucytosine are used. In addition to conservative therapy, the management tactics for patients with chromoblastomycosis also include surgical treatment consisting of the removal of affected tissues. Information on specific antifungal drugs used to treat eumycetoma (Madura foot) is absent from the provided materials. It is only known that mycetoma is a polyetiological disease whose causative agents are Pseudallescheria, Madurella, Acremonium, Leptosphaeria, and other fungi.
SSCM (Sporotrichosis, Chromoblastomycosis, Phaeohyphomycosis, Mycetoma) is an acronym for remembering the four main nosological forms of subcutaneous mycoses.
Class and exam questions
Where are the causative agents of subcutaneous mycoses found in nature?
Their primary natural reservoir is soil, wood, as well as rotting and decaying plant parts.
What is the mechanism of transmission for this group of infections?
The mechanism of infection is traumatic. Fungi are introduced into tissues through skin microtraumas caused by splinters, thorns, or other contaminated foreign objects.
Which tissues are affected in subcutaneous mycoses?
The process goes deeper than the epidermis, sequentially involving the deep layers of the dermis, subcutaneous tissue, fascia, and muscles.
What does "polyetiological disease" mean using mycetoma as an example?
This means that eumycetoma (mycetoma) can be caused by many different genera of fungi, such as Pseudallescheria, Madurella, Acremonium, and Leptosphaeria.
What else to study on this topic
- Morphological features of Sporothrix schenckii
- Specifics of pigmented fungi in chromoblastomycosis
- Properties of dematiaceous (dark-colored) fungi
- Differential diagnosis of eumycetoma pathogens
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