Dermatophyte

Dermatophytes (from Greek δέρμα derma 'skin' (GEN δέρματος dermatos) and φυτόν phyton 'plant') are a common label for a group of three types of fungus that commonly causes skin disease in animals and humans. These anamorphic (asexual or imperfect fungi) mold genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera. Species capable of reproducing sexually belong in the teleomorphic genus Arthroderma, of the Ascomycota (see Teleomorph, anamorph and holomorph for more information on this type of fungal life cycle). Dermatophytes (from Greek δέρμα derma 'skin' (GEN δέρματος dermatos) and φυτόν phyton 'plant') are a common label for a group of three types of fungus that commonly causes skin disease in animals and humans. These anamorphic (asexual or imperfect fungi) mold genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera. Species capable of reproducing sexually belong in the teleomorphic genus Arthroderma, of the Ascomycota (see Teleomorph, anamorph and holomorph for more information on this type of fungal life cycle). 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 dematophytes are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate 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. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection. Some of these skin infections are known as ringworm or tinea (which is the Latin word for 'worm'), though infections are not caused by worms. It is thought that the word tinea (worm) is used to describe the snake-like appearance of the dermatophyte on skin. Toenail and fingernail infections are referred to as onychomycosis. Dermatophytes usually do not invade living tissues, but colonize the outer layer of the skin. Occasionally the organisms do invade subcutaneous tissues, resulting in kerion development. Infections by dermatophytes affect the superficial skin, hair, and nails are named using 'tinea' followed by the Latin term for the area that is affected. Manifestation of infection tends to involve erythema, induration, itching, and scaling. Dermatophytoses tend to occur in moist areas and skin folds. The degree of infection depends on the specific site of infection, the fungal species, and the host inflammatory response. Although symptoms can be barely noticeable in some cases, dermatophytoses can produce 'chronic progressive eruptions that last months or years, causing considerable discomfort and disfiguration.' Dermatophytoses are generally painless and are not life-threatening. Contrary to the name, tinea pedis does not solely affect athletes. Tinea pedis affects men more than women, and is uncommon in children. Even in developed countries, tinea pedis is one of the most common superficial skin infections by fungi. The infection can be seen between the toes (interdigital pattern) 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. The lesions may be accompanied by peeling, maceration (peeling due to moisture), and itching. Later stages of tinea pedis might include hyperkeratosis (thickened skin) of the soles, as well as bacterial infection (by streptococcus and staphylococcus) or cellulites due to fissures developing between the toes., Another implication of tinea pedis, especially for older adults or those with vascular disease, diabetes mellitus, or nail trauma, is onychomycosis of the toenails. Nails become thick, discolored, and brittle, and often onycholysis (painless separation of nail from nail bed) occurs.