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INFECTIOUS DISEASE BACTERIOLOGY IMMUNOLOGY MYCOLOGY PARASITOLOGY VIROLOGY

VIDEO LECTURE


MYCOLOGY - CHAPTER FOUR  

SUPERFICIAL MYCOSES 

Dr Arthur DiSalvo 

 

 
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  The superficial (cutaneous) mycoses are usually confined to the outer layers of skin, hair, and nails, and do not invade living tissues. The fungi are called dermatophytes. Dermatophytes, or more properly, keratinophilic fungi, produce extracellular enzymes (keratinases) which are capable of hydrolyzing keratin.
tinea1.jpg (43982 bytes)   Figure 1 Onychomycosis due to Trychophyton rubrum, right and left great toe. Tinea unguium. CDC/Dr. Edwin P. Ewing, Jr. 
epe1@cdc.gov 

tinea2.jpg (50788 bytes)  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



CLINICAL MANIFESTATIONS 

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." Tinea versicolor is caused by Malassezia furfur (figure 2).
 

ECOLOGY

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

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

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

geophilic - These are usually found in the soil and are 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 4.
A child with ringworm of the scalp, called “tinea capitis”, caused by a Microsporum sp.. Tinea capitis is an infection of the scalp caused by mold-like fungi called dermatophytes, which thrive in warm, moist areas. Susceptibility to tinea infection is increased by poor hygiene, prolonged moist skin, and minor skin or scalp injuries.
CDC

Figure 5.
 Ringworm of the bearded areas of the face and neck, known as “tinea barbae”, or “barber’s itch”. Tinea barbae is due to a dermatophytic infection around the bearded area of men. Generally, the infection occurs as a follicular inflammation, or as a cutaneous granulomatous lesion, i.e. a chronic inflammatory reaction.
CDC

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.
CDC/Dr. Lucille K. Georg

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
 

tricho.jpg (538013 bytes)  Figure 9 Trichophyton mentagrophytes contracted from a dog  © Bristol Biomedical Image Archive. Used with permission
ring2.jpg (532842 bytes)
 Figure 10  Dermatomycosis (ringworm) of hair follicles © Bristol Biomedical Image Archive. Used with permission



ETIOLOGIC AGENTS

There are three genera of dermatophytes:

  • Trichophyton species (19 species) (figure 9).

These infect skin, hair and nails. They rarely cause subcutaneous infections, in immuno-compromised individuals. Trichophyton species take 2 to 3 weeks to grow in culture. The conidia are large (macroconidia), smooth, thin-wall, septate (0-10 septa), and pencil-shaped; colonies are a loose aerial mycelium that 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. It can rarely cause sub-cutaneous infections (kerion) in immunocompromized individuals, particularly  patients with chronic myelogenous leukemia
 

  Figure 10A Trichophyton conidia are large, smooth, thin-walled, septate, and pencil-shaped
Dr Arthur DiSalvo
 
conid.jpg (521855 bytes)  Figure 11A Ringworm, stained preparation, macroconidia of Microsporum canis  © Bristol Biomedical Image Archive. Used with permission

  Figure 11B
Microsporum species: Thick wall, spindle shape, multicellular
Dr Arthur DiSalvo

 

ringcalc-an.jpg (38157 bytes) 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

ring1.jpg (261894 bytes)  Figure 13 Ringworm caused by Microsporum gypseum, culture plate with Sabouraud's dextrose agar 
© Bristol Biomedical Image Archive. Used with permission

Figure 14
Epidermophyton floccosum
Dr Arthur DiSalvo

 
  • Microsporum species (13 species). These may infect skin and hair, rarely nails. The prevalence of infection has decreased significantly in recent years. When prevalent (15-20 years ago), this organism could be easily identified on the scalp because infected hairs fluoresce a bright green color when illuminated with a UV-emitting Wood's light. The loose, cottony mycelia produce macroconidia (figure 11A and B) which are thick-walled, spindle-shaped, multicellular, and echinulate (spiny). Microsporum canis is one of the most common dermatophyte species infecting humans.

 

  • 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 (figure 14).

 

THERAPY 

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

Tolfnatate (Tinactin) available over the counter - Topical 

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

Itraconazole - oral

Terbinifine (Lamisil) - oral, topical. 

Echinocandins (caspofungin) 

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.

 

THE DERMATOPHYTID 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.

 

 

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