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