DERMATOPHYTOSIS

Dermatophytosis is a clinical condition caused by fungal infection of the skin in humans, pets such as cats, and domesticated animals such as sheep and cattle. The term "ringworm", commonly used to refer to such infections, is a misnomer, since the condition is caused by fungi of several different species and not by parasitic worms. The fungi that cause parasitic infection (dermatophytes) feed on keratin, the material found in the outer layer of skin, hair, and nails. These fungi thrive on skin that is warm and moist, but may also survive directly on the outsides of hair shafts or in their interiors. In pets, the fungus responsible for the disease survives in skin and on the outer surface of hairs.

It has been estimated that currently up to twenty percent of the population may be infected by ringworm or one of the other dermatophytoses. It is especially common among people who play sports, wrestling in particular. Wrestlers with ringworm may be withheld from competition until their skin condition is deemed non-infectious by the proper authorities.^[1]

Classification

A number of different species of fungi are involved. Dermatophytes of the genera Trichophyton and Microsporum are the most common causative agents. These fungi attack various parts of the body and lead to the conditions listed below. Note that the Latin names are for the conditions (disease patterns), not the agents that cause them. The disease patterns below identify the type of fungus that causes them only in the cases listed:

·         Dermatophytosis

·         Tinea pedis (athlete's foot) affects the feet

·         Tinea unguium affects the fingernails and toenails

·         Tinea corporis affects the arms, legs, and trunk

·         Tinea cruris (jock itch) affects the groin area

·         Tinea manuum affects the hands and palm area

·         Tinea capitis affects the scalp

·         Tinea barbae affects facial hair

·         Tinea faciei (face fungus) affects the face

·         Other superficial mycoses (not classic ringworm, since not caused by dermatophytes)

·         Tinea versicolor caused by Malassezia furfur

·         Tinea nigra caused by Hortaea werneckii

Signs and symptoms

Infections on the body may give rise to typical enlarging raised red rings of ringworm, infection on the skin of the feet may cause athlete's foot and in the groin jock itch. Involvement of the nails is termed onychomycosis, and they may thicken, discolour, and finally crumble and fall off.

They are common in most adult people, with up to 20 percent of the population having one of these infections at any given moment.^{[citation needed]}

Dermatophytosis tends to get worse during summer, with symptoms alleviating during the winter.^{[citation needed]} Animals such as dogs and cats can also be affected by ringworm and the disease can be transmitted between animals and humans (zoonotic disease).

Causes

Fungi thrive in moist, warm areas, such as locker rooms, tanning beds, swimming pools and in skin folds. It can be spread by sharing sport goods, towels, and clothing.

Prevention

Advice often given includes:

·         Avoid sharing clothing, sports equipment, towels, or sheets.

·         Washing clothes in hot water with fungicidal soap after suspected exposure to ringworm.

·         Avoid walking barefoot; instead wear appropriate protective shoes in locker rooms and sandals at the beach.

·         After being exposed to places where the potential of being infected is great, one should wash with an antibacterial and anti-fungal soap or one that contains tea tree oil, which containsterpinen-4-ol.

·         Avoid touching pets with bald spots as they are often carriers of the fungus.

Treatment

Antifungal treatments include topical agents such as miconazole, terbinafine, clotrimazole, ketoconazole, or tolnaftate(TRIBACT) applied twice daily until symptoms resolve — usually within one or two weeks.Topical treatments should then be continued for a further 7 days after resolution of visible symptoms to prevent recurrence. The total duration of treatment is therefore generally two weeks, but may be as long as three.

In more severe cases or where there is scalp ringworm, systemic treatment with oral medications may be given.

To prevent spreading the infection, lesions should not be touched, and good hygiene maintained with washing of hands and the body.

Misdiagnosis and treatment of ringworm with a topical steroid, a standard treatment of the superficially similar pityriasis rosea, can result in tinea incognito, a condition where ringworm fungus will grow without typical features like a distinctive raised border.

History

Dermatophytosis has been prevalent since before 1906, at which time ringworm was treated with compounds of mercury or sometimes sulfur or iodine. Hairy areas of skin were considered too difficult to treat, so the scalp was treated with x-rays and followed up with antiparasitic medication.

 Clinical manifestations:

The common anthropophilic species are primarily parasitic on man (Table 1). They are unable to colonise other animals and they have no other environmental sources. On the other hand, geophilic species normally inhabit the soil where they are believed to decompose keratinaceous debris.

Some species may cause infections in animals and man following contact with soil. Zoophilic species are primarily parasitic on animals and infections may be transmitted to humans following contact with the animal host (Table 1).

Zoophilic infections usually elicit a strong host response and on the skin where contact with the infective animal has occurred ie arms, legs, body or face.

Table 1. Ecology of Common Human Dermatophyte Species.

Species	Natural habitat	Incidence
Epidermophyton floccosum	Humans	Common
Trichophyton rubrum	Humans	Very Common
Trichophyton interdigitale	Humans	Very Common
Trichophyton tonsurans	Humans	Common
Trichophyton violaceum	Humans	Less Common
Trichophyton concentricum	Humans	Rare*
Trichophyton schoenleinii	Humans	Rare*
Trichophyton soudanense	Humans	Rare*
Microsporum audouinii	Humans	Less Common*
Microsporum ferrugineum	Humans	Less Common*
Trichophyton mentagrophytes	Mice, rodents	Common
Trichophyton equinum	Horses	Rare
Trichophyton erinacei	Hedgehogs	Rare*
Trichophyton verrucosum	Cattle	Rare
Microsporum canis	Cats	Common
Microsporum gypseum	Soil	Common
Microsporum nanum	Soil/Pigs	Rare
Microsporum cookei	Soil	Rare

* Geographically restricted.

Diagnosis

Ringworm in pets may often be asymptomatic, resulting in a carrier condition which either infects other pets. In some cases, the disease only appears when the domestic animal develops an immunosuppressive condition. Circular bare patches on the skin suggest the diagnosis but no lesion is truly specific to the fungus (similar patches may result from allergies, sarcoptic mange, and other conditions). Three species of fungi cause 95% of dermatophytosis in pets:^{[citation needed]} these are Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes.

Veterinarians have several tests to identify ringworm infection and identify the fungal species that cause it:

Woods Test: This is a black light (ultraviolet light) with a magnifying lens. Only 50% of Microsporum canis will show up as an apple-green fluorescence on hair shafts, under the black light. The other fungi do not show. The fluorescent material is not the fungus itself (which does not fluoresce) but rather an excretory product of the fungus which sticks to hairs. Infected skin does not fluoresce.

Microscopic test: The vet takes hairs from around the infected area and places them in a staining solution to view under the microscope. Fungal spores may be viewed directly on hair shafts. This technique identifies a fungal infection in about 40%–70% of the infections but cannot identify the species of dermatophyte.

Culture Test: This is the most effective but also the most time-consuming way to determine if there is ringworm on a pet. In this test, the veterinarian collects hairs from the pet, or else collects fungal spores from the pet's hair with a toothbrush, or other instrument, and inoculates fungal media for culture. These cultures can be brushed with transparent tape and then read by the vet using a microscope, or can be sent to a pathological lab. The three common types of fungi which commonly cause pet ringworm can be identified by their characteristic spores. These are different-appearing macroconidia in the two common species of Microspora, and typical microconidia in Trichophyton infections.

Identifying the species of fungi involved in pet infections can be helpful in controlling the source of infection. Microsporum canis, despite its name, occurs more commonly in domestic cats, and 98% of cat infections are with this organism.^{[citation needed]} It can also infect dogs and humans, however. Trichophyton mentagrophytes has a major reservoir in rodents, but can also infect pet rabbits, dogs and horses. Microsporum gypseum is a soil organism and is often contracted from gardens and other such places. Besides humans, it may infect rodents, dogs, cats, horses, cattle, and swine.

Treatment

Pet animals

Treatment requires both systemic oral treatment with most of the same drugs used in humans—terbinafine, fluconazole, or itraconazole—as well as topical "dip" therapy.^[19]

Because of the usually longer hair shafts in pets (as compared to those of humans), the area of infection and possibly all of the longer hair of the pet must be clipped in order to decrease the load of fungal spores clinging to the pet's hair shafts. However, close shaving is usually not done because nicking the skin facilitates further skin infection.

Twice-weekly bathing of the pet with diluted lime sulfur dip solution is effective in eradicating fungal spores. This must continue for 3 to 8 weeks.

Washing of household hard surfaces with 1:10 household hypochlorite bleach solution (too irritating to be used directly on hair and skin) is effective in killing spores.

Pet hair must be rigorously removed from all household surfaces, and then the vacuum cleaner bag (and often the vacuum cleaner itself) discarded when this has been done repeatedly. Removal of all hair is important, since spores may survive 12 months or even as long as two years on hair clinging to surfaces.

Bovines

In bovines, an infestation is difficult to cure, as systemic treatment is out of economic range.

Local treatment (with iodine compounds) is time-consuming, as it needs scraping of crusty lesions. Moreover, it must be carefully conducted using gloves, because of a possible infestation of the worker.

Old car oil has been used by farmers with some success.