Dermatophyte (from Greek derma "skin" (<small>GEN</small> dermatos) and phyton "plant") is a common label for a group of fungus of Arthrodermataceae that commonly causes skin disease in animals and humans. Traditionally, these anamorphic (asexual or imperfect fungi) mold genera are: Microsporum, Epidermophyton and Trichophyton.
Dermatophytes cause infections of the skin, hair, and nails, obtaining nutrients from keratinized material. The organisms colonize the keratin tissues causing inflammation as the host responds to metabolic byproducts. Colonies of dermatophytes are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate the viable tissue of an immunocompetent host. Invasion does elicit a host response ranging from mild to severe. Acid proteinases (proteases), elastase, keratinases, and other proteinases reportedly act as virulence factors. Additionally, the products of these degradative enzymes serve as nutrients for the fungi. It is thought that the word tinea (worm) is used to describe the snake-like appearance of the dermatophyte on the skin. and may spread to the sole of the foot in a "moccasin" pattern. In some cases, the infection may progress into a "vesiculobullous pattern" in which small, fluid-filled blisters are present.
Another implication of tinea pedis, especially for older adults or those with vascular disease, diabetes mellitus, or nail trauma, is onychomycosis of the toenails.
Tinea capitis or scalp ("blackdot") ringworm
Children from ages 3–7 are most commonly infected with tinea capitis.
Tinea manuum or ringworm of the hands
In most cases of tinea manuum, only one hand is involved. Frequently both feet are involved concurrently, thus the saying "one hand, two feet".
Onychomycosis, tinea unguium, or ringworm of the nail
See Onychomycosis
Tinea incognito
Ringworm infections modified by corticosteroids, systemic or topical, prescribed for some pre-existing pathology or given mistakenly for the treatment of misdiagnosed tinea.
Pathogenesis
In order for dermatophytoses to occur, the fungus must directly contact the skin. Likelihood of infection is increased if the skin integrity is compromised, as in minor breaks. Without having to look at the colony, the hyphae, or macroconidia, one can identify the dermatophyte by a simple color test. The specimen (scraping from skin, nail, or hair) is embedded in the DTM culture medium. It is incubated at room temperature for 10 to 14 days. If the fungus is a dermatophyte, the medium will turn bright red. If the fungus is not a dermatophyte, no color change will be noted. If kept beyond 14 days, false positive can result even with non-dermatophytes. Specimen from the DTM can be sent for species identification if desired.
Often dermatophyte infection may resemble other inflammatory skin disorders or dermatitis, thus leading to misdiagnosis of fungal infections. socks, In heterothallic species, interaction of two individuals with compatible mating types are required in order for sexual reproduction to occur. In contrast, homothallic fungi are self-fertile and can complete a sexual cycle without a partner of opposite mating type. Both types of sexual reproduction involve meiosis.
Frequency of species
In North America and Europe, the nine most common dermatophyte species are:
- Trichophyton: rubrum, tonsurans, mentagrophytes, verrucosum, and schoenlenii
Infections occur more in males than in females, as the predominantly female hormone, progesterone, inhibits the growth of dermatophyte fungi. Clinically dosage up to twice the recommended dose might be used due to relative resistance of some strains of dermatophytes.
Tinea pedis is usually treated with topical medicines, like ketoconazole or terbinafine, and pills, or with medicines that contains miconazole, clotrimazole, or tolnaftate.