Anthropophilic (Superficial) Trichophytosis
This form of the disease is transmitted exclusively within the human population. The primary causative agents are T. tonsurans and T. violaceum.
Epidemiology and Transmission Humans are the only hosts, with infections predominantly affecting children. The incubation period lasts several weeks. Transmission occurs through direct contact with an infected person or indirectly via fomites (shared household items).
A notable epidemiological variant is tinea gladiatorum («mat itch»). This pathology occurs among athletes engaged in contact sports such as wrestling. Transmission is direct by skin-to-skin contact, with T. tonsurans being the predominant pathogen.
Clinical Features Superficial trichophytosis clinically presents as oval-shaped skin lesions with pronounced inflammation and scaling in the central area.
A hallmark of this form is the endothrix pattern of hair invasion, where fungal spores accumulate inside the hair shaft. Due to this internal destruction, hairs fracture at the skin surface, creating a pathognomonic clinical sign known as "black dots" within the affected area.
Cultural Characteristics of Anthropophilic Trichophytons
When cultured on nutrient media, the pathogens of superficial trichophytosis exhibit distinct microscopic features essential for laboratory identification.
- Trichophyton tonsurans: Forms a delicate mycelium with a diameter of 2–3 µm, which is sparsely septate. Sporulation is characterized by pear-shaped microconidia, arthrospores, and chlamydoconidia. Macroconidia are extremely rare in cultures of this species.
- Trichophyton violaceum: Features a thin (3–4 µm), tortuous, and sparsely septate mycelium. Sporulation is represented by various chlamydoconidia. A key feature is that arthrospores appear only in older cultures.
Zoanthropophilic (Infiltrative-Suppurative) Trichophytosis
This group encompasses infections transmitted to humans from infected animals. Unlike the anthropophilic variant, zoanthropophilic trichophytosis features a much more severe clinical course with marked tissue inflammation.
The key difference in skin appendage involvement is the ectothrix pattern. In this case, fungal spores form a sheath around the exterior of the hair shaft. Consequently, hairs do not simply break off, but fall out completely from the hair follicles.
Pathogens of the Zoanthropophilic Form
Two major zoophilic trichophytes are clinically significant.
1. Trichophyton mentagrophytes var. mentagrophytes
- Epidemiology: Mice and various domestic animals serve as the primary reservoirs and sources of infection.
- Clinics: The pathological process may localize to the scalp, beard area, nail plates, and the skin of the feet. The disease presents with abscesses and granulomas within the dermis. The hair invasion type is ectothrix (resulting in hair loss).
- Microscopy: Pure cultures reveal a thin (2 µm) septate mycelium. A specific diagnostic marker for this species is the presence of spiral (corkscrew) hyphae. Rounded microconidia (2–4 µm), chlamydoconidia, and elongated macroconidia (8×40 µm) are also observed.
2. Trichophyton verrucosum
- Epidemiology: Cattle (especially calves), horses, donkeys, and goats serve as the most common sources of infection.
- Clinics: Lesions typically develop on exposed skin areas. Large inflammatory foci form, characterized by scalloped (wavy) borders. Hair invasion also follows the ectothrix pattern.
- Microscopy: The culture consists of a septate mycelium. Sporulation includes teardrop-shaped or elongated microconidia and numerous chlamydoconidia. Macroconidia are spherical (40×5 µm) and characteristically arranged in chains, resembling "string of beads".