Dermatophyte

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. 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. The fungi use various proteinases to establish infection in the keratinized stratum corneum. Some studies also suggest that a class of proteins called LysM coat the fungal cell walls to help the fungi evade host cell immune response. The course of infection varies between each case, and may be determined by several factors including: "the anatomic location, the degree of skin moisture, the dynamics of skin growth and desquamation, the speed and extent of the inflammatory response, and the infecting species." The ring shape of dermatophyte lesions result from outward growth of the fungi. The fungi spread in a centrifugal pattern in the stratum corneum, which is the outermost keratinized layer of the skin. For nail infections, the growth initiates through the lateral or superficial nail plates, then continues throughout the nail. For hair infections, fungal invasion begins at the hair shaft. Symptoms manifest from inflammatory reactions due to the fungal antigens. The rapid turnover of desquamation, or skin peeling, due to inflammation limits dermatophytoses, as the fungi are pushed out of the skin. Dermatophytoses rarely cause serious illness, as the fungi infection tends to be limited to the superficial skin. The infection tends to self-resolve so long as the fungal growth does not exceed inflammatory response and desquamation rate is sufficient. If immune response is insufficient, however, infection may progress to chronic inflammation. == Immune response ==

Fortunately, dermatophytoses soon progress from the inflammatory stage to spontaneous healing, which is largely cell-mediated. Fungi are destroyed via oxidative pathways by phagocytes both intracellularly and extracellularly. T-cell-mediated response using TH1 cells are likely responsible for controlling infection. It is unclear whether the antifungal antibodies formed in response to the infection play a role in immunity. Infection may become chronic and widespread if the host has a compromised immune system and is receiving treatment that reduces T-lymphocyte function. Also, the responsible species for chronic infections in both normal and immunocompromised patients tends to be Trichophyton rubrum; immune response tends to be hyporeactive. However, "the clinical manifestations of these infections are largely due to delayed-type hypersensitivity responses to these agents rather than from direct effects of the fungus on the host." == Diagnosis and identification ==

Usually, dermatophyte infections can be diagnosed by their appearance. 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. == Transmission ==

Dermatophytes are transmitted by direct contact with an infected host (human or animal) socks, towels, hotel rugs, sauna, bathhouse, and locker room floors. Also, transmission may occur from soil-to-skin contact. Depending on the species the organism may be viable in the environment for up to 15 months. While even healthy individuals may become infected, there is an increased susceptibility to infection when there is a preexisting injury to the skin such as scars, burns, excessive temperature and humidity. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics. == Classification ==

Dermatophytes are classified as anthropophilic (humans), zoophilic (animals) or geophilic (soil) according to their normal habitat. • Anthropophilic dermatophytes are restricted to human hosts and produce a mild, chronic inflammation. • Zoophilic organisms are found primarily in animals and cause marked inflammatory reactions in humans who have contact with infected cats, dogs, cattle, horses, birds, or other animals. Infection may also be transmitted via indirect contact with infected animals, such as by their hair. 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 • Microsporum: canis, audouinii, and gypseum • Epidermophyton: floccosum • About 76% of the dermatophyte species isolated from humans are Trichophyton rubrum. • 27% are Trichophyton mentagrophytes • 7% are Trichophyton verrucosum • 3% are Trichophyton tonsurans • Infrequently isolated (less than 1%) are Epidermophyton floccosum, Microsporum audouinii, Microsporum canis, Microsporum equinum, Microsporum nanum, Microsporum versicolor, Trichophyton equinum, Trichophyton kanei, Trichophyton raubitschekii, and Trichophyton violaceum. The mixture of species is quite different in domesticated animals and pets (see ringworm for details). == Epidemiology ==

Since dermatophytes are found worldwide, infections by these fungi are extremely common. Infections occur more in males than in females, as the predominantly female hormone, progesterone, inhibits the growth of dermatophyte fungi. == Medications ==

General medications for dermatophyte infections include topical ointments. • Topical medications like clotrimazole, butenafine, miconazole, and terbinafine. • Systemic medications (oral) like fluconazole, griseofulvin, terbinafine, and itraconazole. For extensive skin lesions, itraconazole and terbinafine can speed up healing. Terbinafine is preferred over itraconazole due to fewer drug interactions. == Treatment ==

Tinea corpora (body), tinea manus (hands), tinea cruris (groin), tinea pedis (foot) and tinea facie (face) can be treated topically. Tinea unguium (nails) usually will require oral treatment with terbinafine, itraconazole, or griseofulvin. Griseofulvin is usually not as effective as terbinafine or itraconazole. A lacquer (Penlac) can be used daily, but is ineffective unless combined with aggressive debridement of the affected nail. Tinea capitis (scalp) must be treated orally, as the medication must be present deep in the hair follicles to eradicate the fungus. Usually griseofulvin is given orally for 2 to 3 months. 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. Antibiotics may be necessary to treat secondary bacterial infections that occur in addition to the fungus (for example, from scratching). Tinea cruris (groin) should be kept dry as much as possible. ==See also==