Trichophytosis

Anthroponotic (superficial) trichophytosis

This form of the disease is transmitted exclusively within the human population. The main causative agents are T. tonsurans and T. violaceum.

Epidemiology and transmission routes Only humans are susceptible to the disease, with the vast majority of cases occurring in children. The incubation period lasts several weeks. Infection occurs through close contact with an infected person or indirectly via shared household items.

An interesting epidemiological feature is the existence of a specific form of infection known as "gladiator ringworm". This condition occurs in athletes engaged in contact wrestling sports. The infection is transmitted by contact, and its main causative agent is T. tonsurans.

Clinical presentation Clinically, superficial trichophytosis manifests as the formation of oval lesions on the skin. Marked inflammation and scaling are observed in the central part of these lesions.

This form is characterized by the "endothrix" type of hair involvement, where fungal spores are located inside the hair shaft itself. Due to this internal destruction, hairs break off right at the skin surface, creating a pathognomonic clinical sign — the appearance of "black dots" in the affected area.

Cultural properties of anthropophilic trichophytes

When cultured on nutrient media, the causative agents of superficial trichophytosis demonstrate a number of characteristic microscopic features important for laboratory diagnosis.

• Trichophyton tonsurans: Forms a thin mycelium with a diameter of 2–3 µm, which rarely has septa (cross-walls). Spore formation is characterized by the presence of pear-shaped microconidia, arthrospores, and chlamydospores. Macroconidia are extremely rare in cultures of this species.
• Trichophyton violaceum: Distinguished by a thin (3–4 µm), tortuous, and sparsely septated mycelium. Spore formation is represented by various chlamydospores. An important feature is that arthrospores begin to appear only in old cultures.

Zooanthroponotic (infiltrative-suppurative) trichophytosis

This group of diseases unites infections transmitted to humans from infected animals. Unlike the anthroponotic variant, zooanthroponotic trichophytosis is characterized by a much more severe clinical course with a pronounced tissue inflammatory reaction.

The main difference in the mechanism of skin appendage involvement is the "ectothrix" type. In this case, fungal spores form a sheath on the outside of the hair shaft. As a result of this involvement, hairs do not simply break off but completely fall out of the hair follicles.

Causative agents of the zooanthroponotic form

Let us examine two main representatives of zoophilic trichophytes.

1. Trichophyton mentagrophytes var. mentagrophytes

• Epidemiology: Mice and various domestic animals serve as the primary reservoir and source of infection.
• Clinic: The pathological process can be localized on the scalp, in the beard area, and can also affect the nail plates and the skin of the feet. The disease proceeds with the development of abscesses and granulomas in the skin thickness. Hair involvement type is ectothrix (accompanied by hair loss).
• Microscopy: A thin (2 µm) septate mycelium is detected in pure culture. A specific marker of the species is the presence of spiral (corkscrew) hyphae. Rounded microconidia measuring 2–4 µm, chlamydospores, and elongated macroconidia (8×40 µm) are also identified.

2. Trichophyton verrucosum

• Epidemiology: Cattle (especially calves), as well as horses, donkeys, and goats, most frequently act as the source of infection.
• Clinic: Lesions typically occur on exposed areas of the skin. Large inflammatory foci are formed, whose distinctive feature is scalloped (wavy) edges. Hair involvement also proceeds via the ectothrix type.
• Microscopy: The culture is represented by septate mycelium. Sporulation includes teardrop-shaped or elongated microconidia and numerous chlamydospores. Macroconidia have a spherical shape (40×5 µm) and characteristically arrange in chains, resembling "string of beads".

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of granuloma formation in zooanthroponotic trichophytosis
• Differential diagnosis of Trichophyton species based on macroconidia morphology
• Pathogenesis of the infiltrative-suppurative form of ringworm
• Virulence factors of dermatophytes of the genus Trichophyton

Other topics in the section "Epidermophytoses (microsporia, trichophytosis, favus, rubroophytosis, etc.)"

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