Dermatophytes

Dermatophytes are a group of keratinophilic fungi that cause infections of keratinized tissues such as the skin, hair, and nails in humans and animals. They obtain nutrients by degrading keratin with secreted keratinases, and typically inhabit the superficial layers of the epidermis rather than invading living tissues. Clinically they produce dermatophytoses, commonly referred to by the site, e.g., tinea capitis (scalp), tinea corporis (body), tinea cruris (groin), tinea pedis (foot). Onychomycosis is a frequent nail infection associated with several species.

Most dermatophytes belong to three genera: Trichophyton, Microsporum, and Epidermophyton. Species such as Trichophyton rubrum and Trichophyton mentagrophytes complex, Microsporum canis, and Epidermophyton floccosum are common pathogens in humans. Zoonotic transmission from animals is notable with M. canis; human-to-human transmission can occur for several species. Infections are generally mild but can be more extensive in immunocompromised individuals.

Diagnosis relies on clinical suspicion supported by microscopy of skin scrapings with 10% potassium hydroxide, which reveals hyphae; culture on Sabouraud dextrose agar helps identify species. Wood lamp examination can aid in some species but is not definitive; molecular methods are increasingly used.

Treatment depends on location and severity. Superficial infections often respond to topical antifungals (azoles, allylamines such as terbinafine). Distal nail infections and extensive disease commonly require systemic therapy (terbinafine, itraconazole, or fluconazole) for several weeks to months. Prevention emphasizes good hygiene, avoiding sharing of personal items, and treating infected pets.