MYCOLOGY - CHAPTER FOUR  

SUPERFICIAL MYCOSES  

   Figure 1 Onychomycosis due to Trychophyton rubrum, right and left great toe. Tinea unguium. CDC/Dr. Edwin P. Ewing, Jr. 
epe1@cdc.gov 

  Figure 2 Tinea Versicolor on chest. 
CDC/Dr. Gavin Hart

Figure 3.
A child with a ringworm (tinea) fungal infection on the left side of his face and left ear. “Tinea faciei” or "Tinea capitis" is the name used for infections of the face caused by a dermatophytic fungus, but not including infection of the bearded areas, which are called “tinea barbae”. Tinea faciei infections are uncommon, and are often initially misdiagnosed. CDC

Tinea means "ringworm" or "moth-like". Dermatologists use the term to refer to a variety of lesions of the skin or scalp.

Tinea corporis - small lesions occurring anywhere on the body (figure 6, 7 and 8).

Tinea pedis - "athlete's foot". Infection of toe webs and soles of feet.

Tinea unguium (onychomycosis) - nails. Clipped and used for culture (figure 1).

Tinea capitis - head. Frequently found in children (figure 3 and 4).

Tinea cruris - "jock itch". Infection of the groin, perineum or perianal area.

Tinea barbae - ringworm of the bearded areas of the face and neck (figure 5).

Tinea versicolor - Characterized by a blotchy discoloration of skin which may itch. Up to 25% of the general population may have this lesion at any one time. Diagnosis is usually possible by direct microscopic examination of KOH-treated skin scrapings which show a typical aspect of mycelia and spores described as "spaghetti and meatballs." Caused by Malassezia furfur (figure 2)

B. ECOLOGY

The dermatophytes (skin plants) causing human infections may have different natural sources and modes of transmission:

anthropophilic - usually associated with humans only; transmission from man to man by close contact or through contaminated objects.

zoophilic - usually associated with animals; transmission to man by close contact with animals (cats, dogs, cows) or with contaminated products.

geophilic - usually found in the soil, transmitted to man by direct exposure. Knowledge of the species of dermatophyte and source of infection are important for proper treatment of the patient and control of the source.

Invasion by zoophilic or geophilic organisms may cause inflammatory disease in man.

Geographic distribution: Dermatophytes occur worldwide, but some species have geographically limited distribution.

Figure 6.
Tinea corporis lesions, or “ringworm” on this patient’s arm due to the dermatophytic fungus Trichophyton rubrum. Dermatophytic members of the genus Trichophyton inhabit the soil, humans or animals, and are some of the leading causes of hair, skin and nail infections, or dermatophytosis in their human hosts. CDC

Figure 7.
Patient  with ringworm on the arm, or tinea corporis due to Trichophyton mentagrophytes. The genus Trichophyton inhabits the soil, humans or animals, and is one of the leading causes of hair, skin and nail infections, or dermatophytosis in humans.

Figure 8.
This patient, a native of New Guinea, has Ringworm on the skin of the right axilla and flank due to Trichophyton rubrum. Usually occurring as a skin parasite, or dermatophyte on man and animals, the genus Trichophyton is characterized by colorless spores that can cause ringworm on the body. This condition is called Tinea corporis. CDC/Lucille K. Georg
 

C. ETIOLOGIC AGENTS

There are three genera of dermatophytes:

1. Trichophyton species (19 species) Figure 9.

These infect skin, hair and nails. Rarely can cause subcutaneous infections, in immunocompromised individuals. Take 2-3 weeks to grow in culture. The conidia are large (macroconidia), smooth, thin-wall, septate (0-10 septa), and pencil-shaped; colonies a re a loose aerial mycelium which grow in a variety of colors. Identification requires special biochemical and morphological techniques (figure 10). Trichophyton rubrum is presently the most common cause of tinea in South Carolina.

  Figure 11 Ringworm, stained preparation, macroconidia of Microsporum canis  © Bristol Biomedical Image Archive. Used with permission

Figure 12. Microsporum canis obtained from a skin scraping of a patient with ringworm on the neck acquired from her infected cat. The fungus is identified as a dermatophyte by this calcofluor stain of the skin scrapings viewed at 500X magnification. The calcofluor dye binds to the chitin in the fungus and fluoresces under a fluorescent light. 
© Gloria J. Delisle, Lewis Tomalty, Queens University
Ontario and The MicrobeLibrary

  Figure 13. Ringworm caused by Microsporum gypseum, culture plate with Sabouraud's dextrose agar  © Bristol Biomedical Image Archive. Used with permission

3. Epidermophyton floccosum.  These infect skin and nails and rarely hair. They form yellow-colored, cottony cultures and are usually readily identified by the thick, bifurcated hyphae with multiple smooth, club-shaped macroconidia.

D. THERAPY 

Skin infections can be treated (more or less successfully) with a variety of drugs, such as:

Tolfnatate (Tinactin) available over the counter - Topical 

Clotrimazole - Topical

Miconazole - Topical.

Ketoconazole seems to be most effective for tinea versicolor and other dermatophytes. 

Itraconazole - oral

Terbinifine (Lamisil) - oral, topical. 

For skin and Nail infections. 

Morpholines - oral

For infections involving the scalp and particularly the nails, griseofulvin is commonly used. This antimycotic must be incorporated into the newly produced keratin layer to form a barrier against further invasion by the fungus. This is a very slow process requiring oral administration of the drug for long periods - up to 6 to 9 months for fingernail infections and 12 to18 months for toenail infections. 

Itraconazole and terbinafine are the drugs of choice for onychomycoses.

E. THE IDENTIFICATION REACTION

Patients infected with a dermatophyte may show a lesion, often on the hands, from which no fungi can be recovered or demonstrated. It is believed that these lesions, which often occur on the dominant hand (i.e. right-handed or left-handed), are secondary to immunological sensitization to a primary (and often unnoticed) infection located somewhere else (e.g. feet). These secondary lesions will not respond to topical treatment but will resolve if the primary infection is successfully treated.

Return to the Mycology Section of Microbiology and Immunology On-line

This page copyright 2007, The Board of Trustees of the University of South Carolina
This page last changed on Monday, July 30, 2007
Page maintained by Richard Hunt

Please report any problems to rhunt@med.sc.edu