Dermatophytosis

Ringworm, Tinea,

Last Updated: March 2013

Importance

Dermatophytosis is a common contagious disease caused by fungi known as

dermatophytes. Dermatophytes belong to a group of organisms that are able to break

down the keratin in tissues such as the epidermis, hair, nails, feathers, horns and hooves.

Most of these fungi reside in the soil and are involved in decomposition; however, the

dermatophytes can infect living hosts. Some dermatophytes (anthropophilic species)

are adapted to humans, and are usually transmitted from person to person. Others

(zoophilic species) are adapted to animals. A few (geophilic) species normally live in

the environment, but occasionally act as parasites. The zoophilic and geophilic species

are sometimes transmitted from animals to people. It is also possible for humans to

transmit anthropophilic dermatophytes to animals, although this seems to be

uncommon.

In living hosts, dermatophytes usually remain in superficial tissues such as the

epidermis, hair and nails. Serious consequences are uncommon and infections can be

self-limiting. However, the illness may be disfiguring and uncomfortable, especially

when the lesions are widespread. Economic effects, such as damage to hides, are also

important in livestock. Infrequently, dermatophytes may invade subcutaneous tissues

and (very rarely) other sites, especially in immunocompromised hosts.

Etiology

Dermatophytosis is caused by pathogenic, keratin-digesting fungi in the genera

Microsporum, Trichophyton and Epidermophyton. Members of Microsporum and

Trichophyton cause illness in both humans and animals. E. floccosum is the only species

of Epidermophyton known to cause disease, and it usually affects only people. Some

authors use the term “dermatophytoids” for soil-dwelling members of Microsporum,

Trichophyton and Epidermophyton that are never or rarely associated with disease (e.g.,

T. terrestre).

Dermatophytes, like many fungi, may have two different species names. One name

belongs to the asexual form (the anamorph state), which is the form that occurs in

vertebrate hosts. The other name is given to the sexual state of the organism. The latter

form, called the teleomorph form or the “perfect state,” is produced by mating between

anamorphs. For example, the dermatophyte Microsporum canis infects animals;

however, when this organism mates with a compatible environmental organism, the

resulting sexual form is called Arthroderma otae. The teleomorph (perfect) states of

both Microsporum and Trichophyton belong to the genus Arthroderma, and

dermatophytes known to have sexual states are placed in the phylum Ascomycota,

family Arthrodermataceae. Dermatophytes that currently have no known sexual state,

like other medically important fungi with this characteristic, are classified as

Deuteromycota (Fungi Imperfecti).

Although dermatophytes originated from soil-dwelling keratinophilic organisms,

only a few pathogenic species still reside primarily in this niche. These organisms,

known as geophilic dermatophytes, are associated with decomposing keratin sources in

the environment. M. gypseum and M. nanum are the only two geophilic dermatophytes

that are important pathogens in animals. M. gypseum is also seen in people, but M.

nanum occurs infrequently.

Most species that cause dermatophytosis have become adapted to people or

animals, and are now maintained in these reservoirs. Although they can infect other

hosts, each dermatophyte tends to be associated with a particular host or group of hosts,

and it is not maintained in other species long term. Zoophilic dermatophytes are adapted

to various animal species, while anthropophilic dermatophytes occur in humans.

Zoophilic Microsporum species include Microsporum canis, M. gallinae and M.

persicolor. Most sources no longer use the name M. equinum for the organisms found

in horses, but consider them to be equine-adapted M. canis. Zoophilic members of

Trichophyton include Trichophyton equinum, T. bullosum, members of the T.

mentagrophytes complex, T. simii and T. verrucosum. Most or all zoophilic

dermatophytes are thought to be zoonotic, although some are transferred to people more

often than others.

Dermatophytosis

There are numerous species of anthropophilic

dermatophytes, including T. tonsurans, the T. rubrum

complex, T. violaceum, T. mentagrophytes var. interdigitale,

T. soudanense, T. schoenleinii, M. audouinii, E. floccosum

and others. Although anthropophilic dermatophytes can be

transmitted to animals, this seems to be rare.

The predominant dermatophytes involved in human

cases vary with the climate, geographic location and other

factors such as exposure to livestock, pets or exotic species.

Zoophilic dermatophytes can be a common cause of a

syndrome in one region, while anthropophilic dermatophytes

account for most cases in another. The causative agents can

also change over time, with some species becoming less

common (e.g., due to the introduction of effective treatments

or changes in exposure) and others becoming more

prevalent.

Dermatophyte taxonomy

The taxonomy of the dermatophytes, particularly

members of T. mentagrophytes, is controversial. Organisms

may be assigned different names depending on whether the

source is using traditional identification methods or genetic

typing.

Diagnostic laboratories have traditionally identified

dermatophytes based on their colony and microscopic

morphology, nutritional and biochemical characteristics, and

other factors. Such methods, together with the ecology of an

organism (e.g., its adaptation to a particular host) have given

rise to a number of species names. However, some organisms

that appear to be different species, based on conventional

typing and/or ecology, may be very closely related

genetically. Furthermore, the traditional typing methods

have given rise to a situation where a single anamorph can

have two different teleomorphs, suggesting that such

“species” actually contain more than one species.

A taxonomic method first proposed in 1999 defines

dermatophyte species by genetic techniques, specifically the

sequencing of highly variable internal transcribed spacer

(ITS) regions of the ribosomal DNA. Some authors have

adopted the ITS scheme. Others feel that its adoption is

premature and based on limited data. ITS taxonomy has been

criticized because it may place organisms into the same

species even when they seem to be ecologically distinct

based on their adaptation to different hosts; zoophilic,

anthropophilic or geophilic nature; or distinctive

characteristics such as opposite mating types or ability to

penetrate hair in vitro. In addition, the results of ITS typing

may not agree with the results of genetic analyses based on

other genes. Some sources also use traditional typing

schemes for practical reasons: genetic typing is not widely

used in diagnostic laboratories, and some species defined by

ITS sequencing can be difficult or impossible to identify by

conventional methods. This is especially true for T.

mentagrophytes.

Zoophilic or geophilic species that have new names,

under the ITS genetic system, include the following:

• Horse-adapted isolates of M. canis, which do not

perforate hair in in vitro tests (unlike most M. canis)

and produce few conidia, were formerly called M.

equinum. Based on genetic relatedness, they are

now considered to be M canis.

• The organism known as M. gypseum in the

traditional taxonomy contains both M. gypseum and

M. appendiculatum in the ITS system.

• The species M. gallinae, a zoophilic organism

found in birds, includes the geophilic organism M.

vanbreuseghemii in the ITS system.

• T. verrucosum varieties have been eliminated under

the current ITS genetic taxonomy, and this

organism is redefined to include only the species

adapted to cattle. The ITS system reassigns T.

verrucosum var. autotrophicum, which occurs in

sheep, to T. interdigitale.

• The ITS system made major changes in the

taxonomy of T. mentagrophytes. In traditional

taxonomy, zoophilic and anthropophilic isolates of

T. mentagrophytes can be separated, in part, by their

different colony morphologies on primary isolation.

The species T. mentagrophytes var interdigitale is

anthropophilic in this system, and mainly contains

isolates associated with tinea pedis (athlete’s foot)

and infections of the nails. Under the ITS

taxonomy, however, most of the organisms that

previously belonged to T. mentagrophytes were

placed in this variety, and it was elevated to the

level of a species (T. interdigitale). Thus, T.

interdigitale in the ITS system includes both

anthropophilic organisms (the former T.

mentagrophytes var. goetzii, T. mentagrophytes var.

interdigitale, T. mentagrophytes var. nodulare and

T. krajdenii) and zoophilic organisms, including the

former T. mentagrophytes var. mentagrophytes, T.

mentagrophytes var. granulosum and T.

verrucosum var. autotrophicum. Under this system,

T. mentagrophytes still contains the former T.

mentagrophytes var. quinckeanum and two camel-

associated species, T. langeronii and T. sarkisovii.

In addition, the authors of the ITS scheme suggest

that all three of these species are associated with

camels, although T. mentagrophytes var

quinckeanum was previously linked mainly with

mice. The association of the latter organism with

camels has been disputed, and the entire

reorganization of T. mentagrophytes is

controversial.

• Two other varieties of T. mentagrophytes received

new names in the ITS system. T. mentagrophytes

var. erinacei, which is adapted to hedgehogs, is now

considered to be the species T. erinacei. In addition,

Dermatophytosis

isolates of T. mentagrophytes found mainly in

guinea pigs (which were usually identified as T.

mentagrophytes var. granulosum) are now called

“the Trichophyton anamorph of A. benhamiae.”

This anamorph was not given a separate species

name. Although it is sometimes shortened to “A.

benhamiae” in clinical literature, the A. benhamiae

complex also contains several other organisms

(e.g., T. erinacei, T. verrucosum and the

anthropophilic organism T. concentricum).

It should be noted that species names, as currently

defined under the ITS genetic taxonomy, may change in the

future. For instance, T. equinum, which is adapted to horses,

was reassigned to the anthropophilic species T. tonsurans at

one time; however, it was later acknowledged to be a

different species.

This factsheet generally uses the traditional taxonomy.

Geographic Distribution

Dermatophytes grow best in warm and humid

environments and are, therefore, more common in tropical

and subtropical regions. Their distribution varies with the

organism. M. canis, M. nanum, M. gypseum, T.

mentagrophytes, T. verrucosum and T. equinum, occur

worldwide, although their prevalence varies with the region.

T. simii was thought to be endemic only in Asia, specifically

the Indian subcontinent; however, infections acquired in

Europe and Africa suggest that its distribution might be more

widespread.. T. mentagrophytes var. erinacei (T. erinacei) is

associated with hedgehogs, and it is found where these

animals occur in the wild (Europe, New Zealand and Africa),

or in countries where they are kept as pets. M. persicolor has

been reported in Europe, and T. bullosum has been detected

in Tunisia, Sudan, Syria and France.

Like zoophilic species, anthropophilic dermatophytes

may be either cosmopolitan or more limited in their

distribution. The latter group may be imported into other

countries on infected individuals.

Transmission

People and animals become infected by dermatophytes

after contact with spores (conidia). Dermatophytes growing

in a vertebrate host normally form only arthrospores

(arthroconidia), asexual spores that develop within the

hyphae. In the environment (e.g., in laboratory culture), they

can also produce microconidia and macroconidia, asexual

spores that develop outside the hyphae. Initially, the

dermatophyte infects a growing hair or the stratum corneum

of the skin. These organisms do not usually invade resting

hairs, since the essential nutrients they need for growth are

absent or limited. Hyphae spread in the hairs and keratinized

skin, eventually developing infectious arthrospores.

Anthropophilic and zoophilic dermatophytes are mainly

transmitted between hosts by arthrospores in hairs or skin

scales. Other asexual or sexual spores formed by the

environmental stages may also be infectious. Fomites such

as brushes and clippers are important in transmission. Spores

may remain viable in suitable environments for up to 12-20

months, and some spores were also reported to persist for at

least a year in salt water. Certain types of spores (e.g.,

microconidia) might be dispersed by airborne means.

Disinfection

Dermatophyte spores are susceptible to benzalkonium

chloride, dilute chlorine bleach (1% sodium hypochlorite),

enilconazole (0.2%), formaldehyde and some strong

detergents. In one study, a 10% solution of

alkyldimetylbenzylammonium chloride prevented the growth

of M. canis from 97% of contaminated hairbrushes, and

Virkon-S® was effective on 87%. Another study found that a

preparation containing benzylammonium bromide and

ethoxyllauric alcohol was effective against the anthropophilic

fungi usually found on swimming room floors. Dermatophytes

are also reported to be susceptible to iodophors,

glutaraldehyde and phenolic compounds; however, some

agents may have limited efficacy in “real life” environmental

disinfection.

The mechanical removal of any material containing

keratin, such as shed skin and hairs, facilitates disinfection.

Vacuuming is considered to be the best method in many

cases. Dusting may also be appropriate. After mechanical

removal, washable surfaces should be cleaned thoroughly

with detergent and water.

Dermatophytes are susceptible to high heat. Moist heat

of 121°C, applied for at least 20 minutes, or dry heat of 165-

170°C for 2 hours, are reported to be effective.

Infections in Humans

Incubation Period

The incubation period in humans is usually 1 to 2 weeks.

Clinical Signs

Dermatophytes generally grow only in keratinized tissues

such as hair, nails and the outer layer of skin; the fungus

usually stops spreading where it contacts living cells or areas

of inflammation. Many dermatophytes can invade hairs as

well as the skin; however, some anthropophilic species such

as E. floccosum and T. rubrum are limited to the skin. Mucus

membranes are not affected.

The symptoms of dermatophytosis vary, depending on

the infecting organism, affected tissues (e.g., skin, hair or

nails) and area of the body. In unhaired (glabrous) skin, the

lesions are usually characterized by inflammation that is

most severe at the edges, with erythema, scaling and

occasionally blister formation. The central area may clear,

resulting in the formation of a classic “ringworm” lesion.

In haired areas, the hairs become brittle and areas of

alopecia may appear. Dermatophytes acquired from

animals or the soil generally produce more inflammatory

lesions than anthropophilic dermatophytes (but not all

individual cases are highly inflammatory). These infections

are also less likely to become chronic than those caused by

anthropophilic organisms

Dermatophytosis

In humans, dermatophytoses are referred to as “tinea”

infections, and are named according to the area of the body

involved. Infections can, however, spread from one area to

another. For example, tinea faciei (facial dermatophytosis) in

children may result from a tinea capitis (scalp) infection that

has spread to the face.

Tinea capitis

Tinea capitis, most often seen in children, is a

dermatophyte infection of the hair and scalp. The major

organisms involved in this condition vary with the

geographic area. M. canis, a zoophilic species, is often

isolated from tinea capitis cases in continental Europe;

however, the anthropophilic dermatophyte T. tonsurans is

currently responsible for most cases in the U.S. and the U.K.

Other anthropophilic organisms, whose importance varies

with the region, include T. violaceum, M. audouinii, T.

schoenleinii, T. megninii, T. soudanense and others. The

zoophilic organisms T. mentagrophytes, T. verrucosum, M.

persicolor and other species, as well the geophilic organisms

M. gypseum and (uncommonly) M. nanum, have been

isolated from some cases.

Tinea capitis is characterized by spreading, scaly,

irregular or well-demarcated areas of erythema and alopecia.

Some anthropophilic dermatophytes may cause dry alopecic

patches with minimal inflammation (sometimes with black

dots where the hairs break at the follicle). Zoophilic

dermatophytes are more likely to cause inflammatory, and in

some cases suppurative, lesions, including .boggy,

inflammatory masses called kerions. An anthropophilic

species, T. schoenleinii, causes “favus,” a chronic infection

characterized by yellow, cup shaped crusts (scutulae) around

the hairs. Untreated cases of tinea capitis can last for a month

to several years, depending on host factors and the species of

dermatophyte involved.

Tinea corporis

Tinea corporis, or ringworm, occurs on the trunk and

extremities (and in some definitions, the face). Infections

often spread to the neck and wrists of adults in contact with

infected children. Anthropophilic organisms that cause tinea

corporis include T. rubrum and E. floccosum, which infect

the skin but not the hair, as well as dermatophytes also found

in tinea capitis, such as M. audouinii, T. schoenleinii, T.

tonsurans and T. violaceum. Various zoophilic organisms

such as M. canis, T. verrucosum, T. equinum, T.

mentagrophytes and M. persicolor, as well as the geophilic

organisms M. gypseum and M. nanum can also cause this

form of tinea.

One or more lesions may be present in tinea corporis.

These lesions are usually pink to erythematous or scaly, and

annular with a slightly elevated, scaly and/or erythematous

edge, sharp margin, and central clearing. Follicular papules,

pustules or vesicles may be found on the borders, especially

when the lesion is caused by zoophilic or geophilic organisms.

The zoophilic organism T. quinckeanum can cause scutulae. In

contrast, some anthropophilic dermatophytes can cause

chronic lesions with little inflammation and very little scaling

at the edge. Lesions are variably pruritic. Treatment with

corticosteroids, or repeated shaving or occlusion of the

affected area, can result in skin lesions that do not resemble

the classic form. Untreated tinea corporis may resolve within

a few months, particularly if it is caused by a zoophilic or

geophilic organism, but infections caused by anthropophilic

organisms may be more persistent.

Tinea faciei and tinea barbae

Tinea faciei and tinea barbae are dermatophyte

infections occurring on the face. These infections are often

acquired from pets or livestock, but they can also be caused

by anthropophilic dermatophytes that originally affected

other parts of the body such as the scalp or torso.

Tinea barbae is an infection of the hairs and skin in the

beard and mustache area, and is usually seen in men. Some

causative organisms invade the hair and hair follicles, while

others (e.g., T. rubrum) are limited to the skin. The lesions of

tinea barbae may include scaling, follicular pustules and

erythema. The zoophilic organisms T. verrucosum

(associated with cattle) and T. mentagrophytes can cause a

very inflammatory form of this disease, with pustular

folliculitis or kerions. Some other species that may be

involved include M. canis, which is zoophilic, and the

anthropophilic organisms T. tonsurans, T. megninii and T.

violaceum. Some authors consider tinea barbae to be a form

of tinea faciei, rather than a separate condition.

Tinea faciei is seen on the nonbearded parts of the face.

It can be caused by a number of anthropophilic and zoophilic

organisms including T. rubrum, T. tonsurans, T.

schoenleinii, T. mentagrophytes, M. canis and T. erinacei.

The lesions are usually pruritic; itching and burning may

become worse after exposure to sunlight. While some lesions

may resemble those of tinea corporis, others have little or no

scaling or lack raised edges. In addition, the areas of

erythema may be indistinct. Due to these atypical

presentations, tinea faciei is often confused with other skin

diseases that affect the face.

Tinea cruris

Tinea cruris is an acute to chronic infection of the groin

and adjacent areas, usually caused by anthropophilic

dermatophytes. The most commonly involved organisms are

T. rubrum, T. mentagrophytes var. interdigitale and

E. floccosum, although the last species is now uncommon in

some areas. The symptoms include burning, pruritus, and

erythematous lesions with scales, raised, sharply demarcated

borders and central clearing. Pustules and vesicles are

sometimes found at the edges of the lesion. Macerated, moist

exudative forms or lesions with an eczematous appearance

can be present in acute cases, while dry lesions with little

scaling and an annular form are more characteristic of

chronic cases. Hyperpigmentation is common in the central

region as the lesion progresses. The same fungi can cause

tinea cruris and tinea pedis, and the two conditions may be

present concurrently.

Dermatophytosis

Tinea pedis and tinea manuum

Tinea pedis is usually caused by anthropophilic

dermatophytes such as T. rubrum, T. mentagrophytes var.

interdigitale and E. floccosum. Interdigital tinea pedis

(athlete’s foot) is an infection of the foot, characterized

either by dryness, fissures and scales or white, moist

macerated lesions in some or all of the spaces between the

toes. Another form of tinea pedis (the chronic,

erythematosquamous or “moccasin” form) appears as

scaling of the soles and lateral surfaces of the feet, with

variable degrees of inflammation and dryness. A third form

of tinea pedis is characterized by erythema, vesicles,

pustules and bullae mainly on the soles of the feet. The nails

are also involved in many cases.

Tinea manuum is a dermatophyte infection that tends

to affect one hand, although involvement of both hands is

possible. In this form, the palms become diffusely dry,

scaly and erythematous. Inflammatory (vesicular or

pustular) lesions can be seen occasionally. Tinea manuum

is most often caused by anthropophilic dermatophytes,

particularly T. rubrum (cases are frequently an extension of

athlete’s foot) but occasional cases may be caused by

zoophilic organisms such as M. canis, T. mentagrophytes,

T. verrucosum and T. erinacei, or the geophilic organism

M. gypseum.

Tinea unguium

Tinea unguium (or onchomycosis) is a dermatophyte

infection of the nails. It is characterized by thickened,

opaque, discolored, broken and dystrophic nails. The nail

plate may be separated from the nail bed. Toenails are

affected more often than fingernails, and individual nails

are sometimes spared. There are several different forms of

tinea unguium, ranging from superficial, roughened white

patches to almost complete breakdown of the nail. Most

infections are caused by anthropophilic Trichophyton

species, particularly T. rubrum and less frequently T.

mentagrophytes var interdigitale. M. canis has been

involved occasionally in immunosuppressed patients.

Dermatophytes in immunosuppressed

individuals

In immunosuppressed individuals with impaired cell-

mediated immunity (e.g., HIV-infected patients with low T

cell counts, or organ transplant recipients), dermatophytes

can cause extensive lesions. In rare cases, they may also

penetrate more deeply into the skin than usual, resulting in

abscesses, exophytic nodules, and pseudomycetomas

(granulomatous or pyogranulomatous masses surrounding

fungal hyphae). Although pseudomycetomas can also occur

in healthy people, they are less common. Dissemination to

internal organs (e.g., lymph nodes, bones, spleen, brain,

liver) is possible, but very rare. Immunosuppressed patients

may also be extensively infected with species that rarely

affect healthy people, such as M. gallinae.

Communicability

Dermatophytes acquired from animals can be

transmitted between people, but this is uncommon and the

number of transfers is limited. In contrast, anthropophilic

dermatophytes are readily spread from person to person.

Anthropophilic dermatophytes can be transmitted to

animals, although this seems to be rare.

Diagnostic Tests

Diagnosis is based on the history, physical examination,

and microscopic examination of scrapings and hairs from the

lesions, sometimes in conjunction with fungal culture and

other techniques such as Wood’s lamp examination and

histology of the tissues.

Some dermatophytes fluoresce when they are stimulated

by the wavelengths of ultraviolet (UV) light in a Wood’s

lamp. Organisms that exhibit fluorescence include some

strains of the zoophilic dermatophytes M. canis and T.

quinckeanum, as well as a few anthropophilic species, such

as M. audouinii. T. tonsurans and T. violaceum, which are

the most common agents in some regions, are not revealed

by this technique. Certain topical preparations may mask the

fluorescence, and alcohol can either suppress it or cause non-

specific fluorescence.

Dermatophytes can often be detected by microscopic

examination of infected hairs and skin or nail scrapings.

Hyphae rounding up into arthroconidia are diagnostic, but

hyphae alone could be caused by other fungi, including

contaminants. In hairs, arthroconidia may be found outside

(ectothrix) or inside (endothrix) the hair shaft. Skin scrapings

should be taken from the edge of the lesion, and hairs should

be plucked (not cut) from this area. The best hairs to select

are those that fluoresce under a Wood's lamp, or are broken

or scaly. Nail scrapings are generally taken from the nail bed,

or from deeper portions of the nail after removing the outer

layers (except in cases where the infection is entirely

superficial). Samples are usually cleared with potassium

hydroxide (KOH) or other agents to help visualize the

organism. Various stains such as chlorazol black E, Parker

blue-black ink, Swartz-Lamkin stain or Congo red stain may

be added. Fluorescence microscopy, using calcofluor white

or other stains, can also be used to visualize dermatophyte

structures.

Fungal cultures, which identify the species of

dermatophyte, can be useful in understanding the source of

the infection and targeting preventive measures appropriately.

Culture may also be necessary if the diagnosis is uncertain, or

the infection is resistant to standard treatment. However,

recommendations vary in the literature, and uncomplicated

cases are not always cultured in practice. Samples for culture

include hair, skin and nail samples, as for microscopic

examination. In some situations (e.g., infections in sensitive

sites, or the identification of asymptomatic carriers), other

techniques such as brushing the hair, using adhesive tape to

collect samples, or rubbing the area with a sterile toothbrush

or moistened, sterile cotton swab may also be effective.

Dermatophytosis

Colonies appear in 5 days to 4 weeks, depending on the

organism. Colony morphology can differ with the medium.

Descriptions are usually based on Sabouraud agar, but

dermatophyte medium or other fungal culture media can also

be used for isolation. Dermatophyte species can be identified

by the colony morphology; the appearance of microconidia,

macroconidia and other microscopic structures; biochemical

characteristics such as urease production; and nutritional

requirements. Specialized tests such as the ability to penetrate

hairs in vitro, or mating tests (which are usually available only

at reference laboratories) may be used occasionally.

Differential media (e.g., bromocresol purple-milk solids

glucose) can be helpful during differentiation. Some fungal

cultures from infected people are negative.

Histology (biopsy) is occasionally helpful, especially in

deep mycoses and some infections of the nails. The

organisms are visualized best with periodic acid–Schiff

(PAS) staining, although they may also be found in

hematoxylin-eosin stained preparations.

PCR tests have been published for a number of

organisms, and molecular methods of diagnosis might

become more common in the future.

Treatment

Dermatophyte infections are treated with a variety of

topical and oral antifungal drugs.

In immunocompetent patients, topical agents are usually

effective in cases that are limited to glabrous skin (e.g., tinea

corporis, tinea cruris, and tinea pedis). Systemic (oral)

antifungal drugs may be necessary in severe cases, or if the

infection does not respond to treatment or reappears.

Topical agents are ineffective against organisms that

infect the hairs. These infections are usually treated with

systemic antifungals, although topical lotions or shampoos

are sometimes used concurrently to decrease shedding of

fungi and spores, or to help treat kerions. Topical agents may

also be used to treat asymptomatic carriers or prevent

reinfection. Tinea capitis is reported to be more difficult to

treat when it is caused by M. canis than Trichophyton spp.

and may not respond as well to some drugs.

Dermatophyte infections of the nails (tinea unguium) are

usually treated with oral antifungal drugs. Concurrent

therapies may include debridement of the nail or nail avulsion.

Treatment should consider sources of reinfection, such

as pets, family members or other close contacts. Some

authors suggest treating all family members when the case is

caused by certain anthropophilic organisms.

Prevention

Controlling dermatophytes in animals can prevent some

cases of zoonotic dermatophytosis in humans. Infected

animals should be treated, and the premises and fomites

cleaned and disinfected as much as possible. (Some

environments can be difficult to decontaminate.) Contact with

infected animals should be limited, and gloves and protective

clothing should be used if these animals are handled.

Better surveillance, improved living conditions and

improved treatments can decrease the overall prevalence of

anthropophilic dermatophytes, while hygiene, and

prevention of contact are helpful in individual cases.

Measures such as moisture control (e.g., in tinea pedis) are

important in reducing susceptibility to some forms of tinea.

Morbidity and Mortality

Dermatophyte infections are common in people,

although the prevalence varies with the climate and various

risk factors including animal contact. Up to 60% of children

may be affected by tinea capitis in some regions, and more

than 50% of the population in some parts of Europe is

reported to have tinea pedis. With the exception of tinea

cruris (which is typically seen in adults), dermatophytosis is

more common in children.

Exposure to dermatophyte spores does not always lead

to infection. Skin injuries (e.g., burns, maceration or

chafing), as well as high temperatures and humidity, increase

susceptibility. For example, tinea cruris is more common in

hot climates and in people who wear tight clothing.

Most dermatophyte infections are not serious in healthy

people, although some conditions are easier to treat than

others. Infections in glabrous skin usually resolve within 2-4

weeks with treatment. In contrast, dermatophytosis of the nails

may be difficult to cure (although the prognosis is better with

newer drugs), and relapses can occur. In addition, damaged

nails do not always return to a normal appearance even if the

fungal infection is eliminated. Infections with opportunistic

bacteria can cause cellulitis in skin damaged by interdigital

fungal infections, and are a particular concern in diabetics.

Dermatophytosis has the potential to be more serious in

immunosuppressed individuals, who may have atypical and

locally aggressive dermatophyte infections, including

extensive skin disease and subcutaneous abscesses.

Disseminated disease is also possible, though very rare.

Infections in Animals

Species Affected

All domesticated mammals are susceptible to

dermatophytes. Wildlife can also be affected. The most

common agents vary with the host and the geographic region,

and may also be affected by management practices (e.g.,

whether animals can contact other species). Overall, the most

common dermatophytes in domesticated mammals are M.

canis, M. gypseum, T. mentagrophytes, T. verrucosum, T.

equinum and (in pigs) M. nanum. Birds can also be affected by

some organisms, such as M. gallinae and T. mentagrophytes.

Reptiles are not usually affected by the dermatophytes

of mammals or birds; however, rare clinical cases associated

with Trichophyton spp. have been reported in lizards, snakes

(green anacondas, Eunectes murinus) and an olive ridley sea

turtle (Lepidochelys olivacea). One case report in iguanas

identified the species as T. interdigitale, possibly of

anthropophilic origin.

Dermatophytosis

Zoophilic dermatophytes

• Microsporum canis is the most common species of

dermatophyte in cats and dogs, with cats considered

to be the most important reservoir hosts. This

organism is also found regularly in horses and

rabbits, and it has been reported in other animals

including cattle, sheep, goats, camelids and swine.

Isolates that appear to be adapted to horses were

previously called Microsporum equinum, but were

moved to M. canis based on genetic analyses.

• Microsporum gallinae occurs in birds, including

poultry. This organism seems to be uncommon in

wild birds. Infections are reported occasionally in

mammals including livestock, especially in some

parts of the world.

• Microsporum persicolor primarily affects wild

rodents (bank voles and mice). It is found

occasionally in other species, especially rabbits and

pigs, and dogs that burrow and hunt rodents. This

organism infects the skin, but does not invade hairs.

• Trichophyton bullosum has been found in horses. It

is related to T. verrucosum.

• Trichophyton equinum, adapted to horses, is an

important cause of dermatophytosis in this species.

Infections have also been reported in cats, dogs,

goats, sheep and other species.

• Trichophyton langeronii seems to be adapted to

camels.

• Trichophyton mentagrophytes has been reported in

many species of animals, especially rodents and

rabbits. It also affects horses, ruminants, swine,

cats, dogs, birds and other hosts.

• T. mentagrophytes var. erinacei (or T. erinacei)

occurs in the European hedgehog (Erinaceus

europeus) and the African hedgehog (Atelerix

albiventris). It is seen in pet hedgehogs as well as

animals in the wild. This organism sometimes

occurs in hunting dogs.

• T. mentagrophytes var. granulosum affects rodents.

One group of organisms, (identified as “the

Trichophyton anamorph of A. benhamiae” in the

ITS taxonomy) is often associated with guinea pigs,

and appears to the most common dermatophyte in

this species.

• T. mentagrophytes var. quinckeanum has

traditionally been associated with mice. However,

it is considered to be a camel-associated isolate in

the ITS genetic taxonomy.

• Trichophyton sarkisovii seems to be adapted to

camels.

• Trichophyton simii affects nonhuman primates, but

some authors believe the primary host is a ground-

dwelling animal. It has also been reported from

other mammals and birds.

• Trichophyton verrucosum, which is adapted to

cattle, is the most important dermatophyte in this

species. T. verrucosum readily infects other hosts,

especially sheep, goats, South American camelids

and camels, but it can also be found occasionally in

other species such as horses, donkeys, pigs, dogs

and rabbits.

• T. verrucosum var. autotrophicum affects sheep.

Geophilic species

• M. gypseum is detected occasionally in a wide

variety of animals, including cats and dogs,

ruminants, camelids, horses, pigs, rodents, rabbits,

birds and others. It is the most frequently isolated

geophilic dermatophyte in animals.

• M. nanum is the most important agent in swine. This

dermatophyte is thought to be uncommon in most

other species, although it has been found

occasionally in rabbits and cattle.

Anthropophilic species

Anthropophilic dermatophytes are reported infrequently

in animals (although it is possible that some of these reverse

zoonoses are missed). Some species that have been

documented in case reports include M. audouinii, T.

schoenleinii, T. rubrum, T. tonsurans, T. violaceum and E.

floccosum. Livestock (e.g., a goat) as well as pets have been

infected. Potential predisposing factors, such as tumors or

treatment with immunosuppressive drugs, were reported in

some cases.

Incubation Period

Fluorescence produced by some dermatophytes, such as

M. canis, can appear on the fur within 7 days of exposure,

and clinical signs can develop within 2 to 4 weeks.

Clinical Signs

Dermatophytes usually grow only in keratinized tissues

such as hair, nails and the outer layer of skin; the fungus stops

spreading where it contacts living cells or areas of

inflammation. Mucus membranes are not affected.

Dermatophyte lesions in animals are characterized by

areas with varying degrees of alopecia, scaling, crusts and

erythema, and may or may not be pruritic. Hairs in the

affected area are usually brittle and break near the skin

surface, often giving the lesion a “shaved” appearance;

truncated hair shafts may be seen through the scales and

crusts. Occasionally, dermatophytes may die at the center of

a lesion and that area resolves, leaving a circular lesion with

central crusts or hair regrowth. Some degree of folliculitis

occurs in most cases; papules or pustules involving the hair

follicle or conical dilation of the hair follicle ostium are

suggestive of dermatophytosis in small animals.

Asymptomatic infections are also common, particularly in

adult animals.

Dermatophytosis

Cats

Many cats infected with dermatophytes have few or no

lesions. Long-haired adults, in particular, can be subclinical

carriers or have only minimal signs, such as patchy areas of

short stubble, alopecia, scales or erythematous plaques,

visible only on close inspection. More apparent cases tend

to be seen in kittens, with the early lesions often found on

the face, ears and paws. In addition to focal alopecia and

scales, affected areas may develop a thin, grayish white

crust or a thick, moist scab. They may or may not be

pruritic. The cat’s grooming behavior may eventually

spread the infection to the entire body. Other presentations

that have been reported in cats include miliary dermatitis

and recurrent chin acne. Severe cases of dermatophytosis,

with large, erythematous, alopecic, exudative lesions, may

be seen in debilitated cats, or in animals that have been

treated with corticosteroids. Onchomycosis can occur

concurrently in cats with dermatophytosis; the nails may be

opaque, with whitish mottling, and shredding of the nail

surface.

In some cats, dermatophytosis may appear as one or

more firm, subcutaneous nodules known as

pseudomycetomas, Pseudomycetomas tend to occur in long-

haired cats, especially Persians, and are most often found on

the back and the neck. They sometimes ulcerate or form

draining sinus tracts. Some cats, but not others, have

concurrent cutaneous signs such as alopecia and scaling.

True mycetomas have also been reported, though rarely.

Uncomplicated dermatophyte lesions are usually self-

limiting within a few weeks to a few months in short-haired

cats; however, the organisms may persist, either

symptomatically or asymptomatically, in long-haired cats.

Dogs

Dermatophytosis is seen most often in puppies. The

lesions frequently develop on the face and limbs, although

they may occur on any part of the body. M. canis tends to

appear as small circular areas of alopecia. The hairs are

typically broken at the base, giving the appearance of having

been shaved. The center of the lesion usually contains pale

skin scales in the early stage, giving it a powdery appearance,

and the edges are generally erythematous. Vesicles and

pustules may also be seen. In later stages, the area is often

covered by a crust and the edges swollen. Individual lesions

may coalesce to form large, irregular patches. Lesions caused

by T. mentagrophytes and T erinacei tend to be more

thickened and inflammatory than those caused by M. canis,

while M persicolor typically causes localized or generalized

scaling with little erythema and minimal alopecia. Other forms

of dermatophytosis can include kerions (localized severe

inflammation with swollen, boggy skin oozing pus) and

pseudomycetomas. Onchomycosis may occur concurrently

with dermatophytosis.

Although dermatophytosis is often self-limited in dogs,

some animals can develop severe, chronic cases with

widespread lesions, and severe inflammation and alopecia.

Generalized cases in adult dogs usually occur in

immunosuppressed animals, especially those that have

hyperadrenocortictropism or have been treated with

corticosteroids.

Horses

In horses, most dermatophyte lesions are found in areas

of contact with saddles or other tack. They usually begin as

small patches of raised hairs, and progress to hair loss, with

variable amounts of scaling, erythema, crusting and

exudation. M. canis lesions are reported to be milder, in most

cases, than T equinum. Kerions may occur in some animals,

especially on the face. Miliary dermatitis may also be seen,

with small crusted lesions especially on the flanks. Early

dermatophyte lesions can sometimes resemble papular

urticaria, but more characteristic signs develop within a few

days. Lesions may coalesce, especially where the skin is

abraded from tack.

Cattle

In cattle, dermatophytosis varies from small focal

lesions to extensive generalized skin involvement. The initial

lesions may be discrete, scaly and alopecic with grayish-

white crusts, and tend to appear on the face and neck in

calves. Cows and heifers may have lesions more often on the

chest and limbs, and bulls on the dewlap and intermaxillary

skin. Some areas may become suppurative and thickly

crusted. Lesions resembling light brown scabs may also be

seen; when these scabs fall off, they leave an area of alopecia.

The clinical signs usually resolve spontaneously in 2 to 4

months.

Sheep and goats

Dermatophytosis tends to be seen in show lambs, but

appears to be uncommon in production flocks. The most

noticeable signs are usually circular, alopecic areas with

thick scabs on the head, face and non-wooled areas of the

legs; however, widespread lesions may be found under the

wool when lambs are sheared for showing. In healthy lambs,

the disease is usually self-limiting.

Swine

Pigs may develop a wrinkled lesion covered by a thin,

brown, easily removed scab, or a spreading ring of

inflammation. Dermatophyte infections are often

asymptomatic in adult swine.

Rodents

Most rodents infected with T. mentagrophytes are

asymptomatic or have few clinical signs. There may be areas

of partial or complete alopecia, erythema, scales, and crusts

in symptomatic animals. In guinea pigs, the lesions tend to

appear first on the face, then spread to the back and limbs. In

mice, the lesions are often found on the tail.

Rabbits

Focal alopecia, with erythema, crusts, scales and scabs,

is initially seen mainly around the eyes, nose, ears and dorsal

neck. The lesions may later spread to other areas of the body.

The disease is usually self-limiting.

Dermatophytosis

Hedgehogs

Asymptomatic infections are common in hedgehogs. In

symptomatic animals, scales may be found on the head, base

of the nails and under the pads, but lesions are difficult to see

between the spines.

Birds

In cage birds, there may be alopecia and scales,

particularly on the face, head, neck and chest, as well as auto-

mutilation and feather plucking. The head and neck,

especially the comb, are often affected in fowl. The lesions

may include white crusts or plaques and hyperkeratosis.

Although feathers may be lost in birds, they are not infected.

Reptiles

Reptiles are not usually affected by the dermatophytes

of mammals or birds; however, there are rare case reports of

dermal lesions in lizards and green anacondas. Clinical signs

reported during a Trichophyton outbreak in iguanas included

scaling, crusting, thickening of the skin and ulcerative

dermatitis. Trichophyton spp. infection was associated with

papular and pustular cutaneous lesions in a Tenerife lizard.

This animal died of an undetermined illness, soon afterward.

Trichophyton spp. was also detected by

immunohistochemistry from systemic lesions in a moribund

sea turtle.

Communicability

Most animal dermatophytes are readily transmitted to

other susceptible hosts, including humans, by contact and

contamination of the environment. M. nanum of pigs and T.

gallinae of birds are generally reported to be uncommon in

healthy people; however, this may not be the case in all

locations. One study found that T. gallinae was the third most

frequent dermatophyte of children in Nigeria.

Post Mortem Lesions Click to view images

Gross post-mortem lesions are usually identical to those

in live animals; with the exception of pseudomycetomas and

mycetomas, dermatophytes are restricted to the hair, nails

and superficial skin.

Diagnostic Tests

Dermatophytosis is usually diagnosed by a combination

of direct microscopic examination, culture and Wood’s lamp

examination. Biopsy (histopathology) tends to be used

mainly when the presentation is unusual.

A Wood’s lamp examination for fluorescence can be

helpful in detecting some species of dermatophytes, such as

M. canis and T. quinckeanum. Not all strains of these

organisms exhibit fluorescence. Certain topical preparations

may mask the fluorescence, and alcohol can either suppress

it or cause non-specific fluorescence.

Microscopic examination of skin scrapings or plucked

hairs may reveal hyphae or arthroconidia. Hyphae rounding

up into arthroconidia are diagnostic; however, hyphae alone

could be caused by other fungi, including contaminants.

Samples should be selected from the margins of active lesions,

or from the entire lesion if there is no inflammatory margin.

The best hairs to select are those that fluoresce under a

Wood's lamp, or are broken or scaly. Samples are usually

cleared with potassium hydroxide (KOH) to help visualize

the organism, although other clearing agents may be used. A

longer clearing time can be helpful when the hair is thicker

and more heavily pigmented, or if the sample is taken from

a thick, crusted lesion. Various stains such as chlorazol black

E, Parker blue-black ink, Swartz-Lamkin stain, Congo red

stain or Giemsa can aid the visualization of fungal structures.

In practices where fluorescence microscopy is available,

calcofluor white staining can be used.

Skin scrapings or plucked hair samples for culture should

be taken from active lesions, as for microscopic examination.

Nail beds and claws are cultured in cases of onchomycosis.

Swabbing dermatophyte lesions first with alcohol may

decrease contaminants, especially in livestock. Additional

collection methods, which are especially helpful in

asymptomatic animals suspected of being carriers, including

brushing the fur with a disinfected toothbrush or other small

brush, or rubbing it with a sterile piece of carpet.

Dermatophytes can be cultured on various fungal media,

including Sabouraud agar (with cycloheximide and

antibiotics) and dermatophyte test medium (DTM). Cultures

are usually incubated at room temperature (20–28ºC), but

higher temperatures can be used when certain organisms

(e.g., T. verrucosum) are suspected. Colonies often become

visible within 1-2 weeks but, some species grow more slowly

and may require longer to appear. Colony morphology can

differ with the medium; descriptions are usually based on

Sabouraud agar. DTM contains a pH indicator (phenol red)

that will turn the medium red when a dermatophyte is growing.

However, the mycelial growth must also be examined

microscopically, as this color change alone is not diagnostic

and could be produced by other fungal or bacterial organisms.

In addition, the color change may be delayed with certain

dermatophytes such as M. persicolor. In asymptomatic

animals, caution must be used to distinguish infection from

contamination of the coat with organisms from the

environment.

Dermatophyte species can be identified by the colony

morphology; the appearance of microconidia, macroconidia

and other microscopic structures; biochemical characteristics

such as urease production; and nutritional requirements.

Microconidia and macroconidia can be used to distinguish the

genera Microsporum, Trichophyton and Epidermophyton.

Members of Microsporum spp. produce microconidia and

rough-walled, multiseptate macroconidia. The thickness of

the wall, shape and number of macroconidia vary with the

species. Trichophyton spp. produce microconidia and

smooth, thin-walled, cigar shaped macroconidia.

Macroconidia are rarely seen with some species. E.

floccosum, which is anthropophilic and has very rarely been

reported in animals, produces large, thin-walled,

multicellular, club-shaped, clustered macroconidia. This

organism does not produce microconidia. Specialized tests,

such as the ability to penetrate hairs in vitro, or mating tests

Dermatophytosis

performed at reference laboratories, may occasionally be

used in the differentiation process. Differential media (e.g.,

bromocresol purple - milk solids glucose) can also be

helpful.

Histology may be used in some cases, especially in

animals with pseudomycetomas. The organisms are

visualized best with periodic acid–Schiff (PAS) staining,

although they may also be found in hematoxylin-eosin

stained preparations.

PCR tests have been published for a number of

organisms, including zoophilic organisms, and molecular

methods of diagnosis might become more common in the

future.

Treatment

Healthy animals often have self-limiting infections that

resolve within a few months, but treatment can speed

recovery, prevent the lesions from spreading, and decrease

the risk of transmission to people or other animals. Some

individual animals, particularly those that are debilitated or

unusually susceptible, may not clear the infection without

treatment.

Drugs available to treat dermatophytosis in animals

include topical antifungal creams or shampoos, and systemic

antifungals. The same treatment principles apply in animals

as people; however, practical considerations limit the use of

systemic antifungals in some species. Topical drugs are

unable to eliminate dermatophytes from within hairs and hair

follicles, but they may be effective against organisms in

superficial sites (e.g., in the skin), and they can decrease

contamination and transmission to others. The optimal

treatment in small animals is combined topical and systemic

treatment. Systemic antifungals are rarely used in large

animals, due to the cost of these drugs and the typically self-

limited nature of the disease. The side effects of systemic

drugs should also be taken into consideration when choosing

a treatment plan. Clipping the hair before treatment is

controversial. It may aid the penetration of topical drugs, as

well as remove infected hairs. However, it may also result in

trauma to the skin and help disseminate the infection. If the

animal is clipped, this should be done with care.. Some

animals such as cattle develop thick crusts, which should be

removed by gentle brushing.

Onchomycosis can be very difficult to cure; long term

treatment or surgical declawing may be necessary.

Pseudomycetomas and mycetomas are also reported to be

difficult to treat, often recur after surgery, and may not respond

to some drugs. Nevertheless, some cases have been treated

successfully with drugs and/or surgery.

Animals should be isolated until the infection resolves.

Confining the animal to an environment that is easily cleaned

can facilitate environmental control. Dermatophytes can be

difficult to eradicate from environments such as kennels,

catteries and animal shelters.

Prevention

To prevent the introduction of dermatophytes into herds

or kennels, newly acquired animals should be isolated and

cultured. Wild rodent control can decrease exposure to T.

mentagrophytes. Some organisms can be acquired by contact

with infected soil.

To prevent infected animals from transmitting

dermatophytes to others, they should be isolated until the

infection has resolved. The premises should be cleaned and

disinfected. Some environments (e.g., barns) may be difficult

or impossible to decontaminate completely. Animals that

have been in contact with the patient should be checked for

asymptomatic infections. Some veterinarians use topical

antifungals prophylactically for in-contact animals.

Dermatophytes can be difficult to eradicate from

environments such as kennels, catteries and animal shelters.

Successful treatment of these premises must be based on

good environmental control, as well as treatment of

symptomatically and asymptomatically infected animals.

Vaccines are available in some countries for certain

organisms, such as T. verrucosum and T. mentagrophytes in

livestock, farmed foxes, chinchillas and rabbits; T. equinum

in horses; and M canis in cats and dogs. A feline vaccine

licensed for M. canis in the U.S. was found to be ineffective

under field conditions, and was withdrawn by the

manufacturer in 2003. Studies of other vaccines have

demonstrated varying efficacy.

In some countries, vaccines have been used in

dermatophyte eradication campaigns for cattle. In Norway,

there is a program to eradicate T. verrucosum from cattle

herds by vaccination, disinfection of contaminated stables,

isolation of infected animals and good hygiene. In one region

of Norway, where 95% of herds participated, the prevalence

of cattle ringworm decreased from 70% to 0% over a period

of 8 years. In the former Soviet Union, a vaccination

campaign reduced the prevalence of T. verrucosum in cattle

to less than 1% by 1984.

Morbidity and Mortality

Whether an animal becomes infected after contact with

a dermatophyte may depend on the animal’s age, the

condition of its exposed skin, general health and grooming

behavior. Young animals, including puppies, kittens, calves,

lambs and young camelids, are more likely to have

symptomatic infections than adults. Clinical

dermatophytosis is also thought to be more common in

immunosuppressed animals. Most infections in healthy

animals heal spontaneously within one to a few months. Hair

loss is not permanent unless the follicle has been destroyed

by inflammation. Infections can be more persistent or

widespread in young or sick animals. Breeds reported to

more susceptible to dermatophytes include some long haired

cats, and possibly Yorkshire terriers. Long-haired cats,

especially Persians, are also more likely to develop

pseudomycetomas and mycetomas.

Dermatophytosis 
 
www.cfsph.iastate.edu   © 2004-2013  page 11 of 13 
Dermatophytes  can  be  isolated  from  animals  with  or 
without  clinical  signs.  Highly  variable  infection  rates, 
between 6% and 100%, have been reported in surveys of cats, 
which are thought to carry these organisms more often than 
dogs.  Infections  are  especially  prevalent  in  strays  and  in 
catteries. The estimated prevalence among pet cats and dogs 
in individual households is still unclear. While some surveys 
suggest that many cats are infected with these organisms, one 
University of Wisconsin study did not detect dermatophytes in 
any of 182 asymptomatic pet cats that lived alone with their 
owners. 
Among  livestock,  dermatophytes  are  particularly 
common in cold climates where animals are stabled for long 
periods of time. This disease usually becomes endemic in 
cattle herds, where it most often affects animals under a year 
of age. The lesions tend to develop in cattle when they are 
stabled indoors in winter, and to resolve when they are turned 
out in the spring.. Clinical cases do not seem to be common 
in  sheep  and  goats,  with  the  exception  of  show  lambs; 
however, M. canis caused some outbreaks that affected 20-
90% of sheep herds in Australia. It is possible that cases are 
underdiagnosed  in  small  ruminants.  Infected  animals  are 
reported to be common on rabbit farms in some countries. 
Clinical cases seem to be infrequent in birds. 
Internet Resources 
Centers for Disease Control and Prevention (CDC) 
Canadian National Centre for Mycology. World of  
Dermatophytes: A Pictorial 
National Institutes of Health 
The Merck Manual 
The Merck Veterinary Manual 
Acknowledgements 
This factsheet was written by Anna Rovid Spickler, DVM, 
PhD, Veterinary Specialist from the Center for Food 
Security and Public Health. The U.S. Department of 
Agriculture Animal and Plant Health Inspection Service 
(USDA APHIS) provided funding for this factsheet through 
a series of cooperative agreements related to the 
development of resources for initial accreditation training.  
The following format can be used to cite this factsheet. 
Spickler, Anna Rovid. 2013. Dermatophytosis. Retrieved 
from http://www.cfsph.iastate.edu/DiseaseInfo/ 
factsheets.php.  
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