Dermatophytosis

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 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 involving skin to skin contact, wrestling in particular. Wrestlers with ringworm may be withheld from
competition until their skin condition is deemed non-infectious by the proper authorities. 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,
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 affects the feet
Tinea unguium affects the fingernails and toenails
Tinea corporis affects the arms, legs, and trunk
Tinea cruris affects the groin area Tinea manuum affects the hands and palm area
Tinea capitis affects the scalp Tinea barbae affects facial hair
Tinea faciei affects the face Other superficial mycoses
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. Dermatophytosis tends to get worse during
summer, with symptoms alleviating during the winter. Animals such as dogs and cats can also be
affected by ringworm and the disease can be transmitted between animals and humans. 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 contains terpinen-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 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. In veterinary medicine
Clinical conditions Ringworm caused by Trichophyton verrucosum
is a frequent clinical condition in cattle. Young animals are more frequently affected. The lesions are located in head, neck, tail
and perineum. Typical lesion is a round, whitish crust. Multiple lesions may coalesce in “map-like”
appearance. Clinical dermatophytosis is also diagnosed
in sheep, dog, cat, horse. Causative agents, besides Trichophyton verrucosum,
are T. mentagrophytes, T. equinum, Microsporum gypseum, M. canis, and M. nanum. 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. Three species of fungi cause 95% of dermatophytosis
in pets: 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 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 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. 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. Because of the usually longer hair shafts
in pets, 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 is effective in killing spores. Pet hair must be rigorously removed from all
household surfaces, and then the vacuum cleaner bag 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 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. See also
List of cutaneous conditions References External links
The Mycosis Study Group website, with photos, education, fungal treatment regimens
Tinea photo library at Dermnet Slideshow: See Pictures and Learn About Ringworm

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