Aetiology

Dermatophytes may be spread:

  • Directly from one person to another (anthropophilic organisms)

  • Transmitted to humans from soil (geophilic organisms)

  • Spread to humans from animal hosts (zoophilic organisms).

Anthropophilic organisms cause most fungal skin infections, although zoophilic organisms are still common in developing countries. The skin's mechanisms of protection (dryness and shedding of cells) may be breached due to trauma, irritation, or maceration. Indirect transmission of dermatophytes can also occur from fomites (e.g., hats, upholstery, hairbrushes, and combs). Occlusion of the skin with non-porous materials can interfere with the skin's defences by increasing hydration and local temperature.

Host factors[8]

  • Genetic susceptibility, including atopy

  • Ethnicity

  • Immunosuppressive illnesses or medications (e.g., HIV infection, corticosteroids)

  • Presence of other skin diseases that disrupt the epidermis (e.g., atopic dermatitis)

  • Other illnesses that predispose to skin infection, including diabetes mellitus and peripheral vascular disease.

Local factors[9][10]

  • Sweating

  • Occlusion

  • Occupational exposure

  • High humidity (tropical or semi-tropical climates)

  • Exposure to infected pets or farm animals, infected fomites, skin contact with the floors of public bathing facilities

  • Contact sports such as wrestling.

Pathophysiology

Transmission through exposure to infected desquamated cells can occur by direct contact. Inoculation occurs through breaks in the skin where dermatophyte fungi enter; they then germinate, produce keratinases, and invade the superficial skin layers. These fungi require keratin for growth, which means they are restricted to hair, nails, and superficial skin, and do not infect mucosal surfaces.

Classification

Site of infection

  • Dermatophyte infections of the hair and hair follicle and perifollicular skin: tinea capitis, tinea barbae, Majocchi's (trichophytic) granuloma

  • Dermatophyte infections of keratinised epidermal skin: tinea faciale or faciei, tinea corporis, tinea cruris, tinea manuum, tinea pedis

  • Dermatophyte infections of the nail apparatus: tinea unguium (toenails, fingernails)

  • Onychomycosis, a more inclusive term including nail infections caused by dermatophytes, as well as yeasts and moulds

Source of infecting organism[1]

  • People (anthropophilic organisms)

  • Animals (zoophilic organisms)

  • Soil (geophilic organisms)

  • Fomites

Taxonomy

  • Microsporum species

  • Trichophyton species

  • Epidermophyton species

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