SUPERFICIAL MYCOSES

caused by fungi that invade only superficial keratinized tissue (skin, hair and nails) do not invade deeper tissues dermatophytes – most important

Classified into 3 genera:1. Epidermophyton 2. Microsporum 3. Trichophyton

Morphology and Identification

Culture – Sabourauds agar Conidia formation observed in slide

A. Trichophyton (Arthroderma)

Microconidia are the predominant spore form

Smooth-walled, pencil shaped microconidia – rare

Medium on which the fungi grow greatly influences the characteristics of the fungi

Trichophyton mentagrophytes – granular to powdery

- abundant grape-like clusters of subspherical microconidia on terminal branches

- coiled hyphae are common

Trichophyton rubrum – some teardrop-shaped microconidia along the sides of

the hyphae - colonies often develop a red color on the

reverse side

T. rubrum

Trichophyton tonsurans – larger microconidia - usually numerous, maybe borne on short branches

B. Microsporum (Nannizzia)Macroconidia are the predominant clinical form Large, rough-walled, multicellular and spindle shaped – form on the ends of the hyphae Usually infects skin and hair but rarely the nails

M. canis – forms numerous thick-walled 8-15 celled macroconidia that frequently have

curved or hooked spiny tips

-a yellow-orange pigment usually develops on the reverse side of the colony -infected hairs fluoresce bright green under wood’s light

M. canis M. canis culture

M. gypseum – has abundant thinner-walled 4-6 celled macroconidia in buff to

brownish – colored colonies

M. gypseum M. Gypseum culture

M. audouini

M. audouini – rarely forms conidia in the colony - many thick-walled

chlamydospores are present - grows

poorly on sterile rice grains - infected hair fluoresce

Epidermophyton (Floccosum)

only 1-5 celled, club-shaped macroconidia greenish-yellow colony mutates to form a sterile white overgrowth only invade skin and nails

Epidermophyton

Clinical Findings

A. Tinea Pedis (Athletes Foot)

most prevalent of all dermatophytoses infected with Trichophyton species or E. floccosum initially itchy between the toes and development of

small vesicles that rupture and discharge a thin fluid skin of toe becomes macerated and peels off – crack –

prone to secondary bacterial infection – lymphangitis and lymphadenitis develop

when fungal infections becomes chronic – peeling and cracking of the skin are the principal manifestation

= found only in people who wear shoes = infection spreads through the use of common

showers and dressing rooms, where infected, desquamated skin serves as a source of infection

= no really effective control measures (other than proper

hygiene and use of talc to keep interdigital space dry)

= chronic athletes foot – asymptomatic and becomes

activated only in excessive heat or moisture or with unsuitable footwear – open toed shoes/ sandals are best for general wear

Tinea Pedis

Tinea ungium; onychomycosis –follows prolonged tinea pedis

- nails become yellow, brittle, thickened or crumbling

in some instances, the individual may become hypersensitive to constituents or products of the fungus and may develop allergic manifestations called dermatophytids (usually vesicles) elsewhere in the body, most often on the hands

trichophytin skin test – markedly (+)

B. Tinea Corporis (Tinea Glabrosa, Tinea cruris) (Ringworm)dermatophytosis of the non hairy skin of the

body gives rise commonly to the annular lesions

of ringworm ,clearing, scaly center surrounded by a red advancing border that often contains vesicles

T. corporis T. cruris T. Cruris jock itch

C. Tinea capitis (Ringworm of the scalp)

occurs in childhood and usually heals spontaneously by puberty

infection begins on skin of the scalp – subsequent growth of the dermatophyte down to the keratinized wall of the hair follicle

infection takes place just above the hair root fungus continues to grow downward on the upward-

growing hair shaft Microsporum species grow primarily as a sheath

around the hair (ectothrix)some invade the hair shaft (endothrix) – making it fragile – breaks off within or at the surface of hair follicle (black-dot ringworm)

infections with other species – hair breaks a short distance above the scalp – short stubs

in a balding, usually circular patch= redness, edema, scaly and vesicle formation maybe seen = pronounced inflammation are seen in some areas (kerion) – resemble pyogenic infections

T. schoenleinii – forms cup-like crusts (scutula around infected follicle)

D. Tinea barbae – infection with trichophyton species involving the bearded region of humans only occur in immunocompromised persons

Other Superficial Mycosis

Tinea Versicolor Growth within the stratum corneum of clusters of spherical, thick walled budding cells and short bent hyphae of Malassezia furfur – usually causes no pathologic signs except fine to browny scales Lesions appear on chest, back, abdomen, neck and upper arms Lesions range from depigmented to brownish – red and are only of cosmetic importance

Tinea Nigra Light brown to blackish macular areas – palmar or plantar stratum corneum Filled with brownish, branched, septate hyphae and budding cells of Chladosporium werneckii No scaling or other reaction develop

Piedra

Hard black nodules – around the scalp hair by Piedraia hortae

- Softer, white to brown nodules – caused by Trichosporon cutaneum

form on axillary, pubic, beard and scalp hair

Diagnostic Laboratory Test scraping of both skin, nails and hairs plucked from involved areas

A. Microscopic examination Specimen placed on a slide + drop of 10-20% KOH – covered with cover slip – examined immediately and then again after 20 minutes In skin and nails – branching hyphae or chains of arthrospores are seen In hairs – microsporum species form dense sheaths of spores around the hair

- trichophyton species form parallel rows of spores out side. (ectothorix) or inside (endothrix) the hair shaft

B. Culture for final identification of dermatophytes specimens are inoculated into sabourauds agar – 1-3 weeks incubation at room temperature

C. Treatment therapy consist of thorough removal of infected and dead epithelial structures and application of a typical antifungal chemical overtreatment causes dermatophytids attempts must be made to prevent reinfection in widespread infection – Griseofulvin 1-4 weeks nail infection – requires months of griseofulvin

treatment and sometimes surgical removal of the nail

A. Scalp infections Griseofulvin = 0.125 – 0.5g/d orally for 1 – 2

weeks Frequent shampoos and Miconazole cream

2%

B. Body infections Miconazole cream 2% 5% Undecylenic Acid Cream 3% Salicylic Acid 5% Benzoic Acid In tinea vesicolor – selenium sulfide also

effective

C. Foot Infections 1. Acute phase = soak in potassium

permagerate 1: 5,000 until

acute inflammation subsides – apply antifungal chemicals

2. Chronic phase = apply antifungal chemical – cream at night

Control

infection arises from contact of uninfected skin or hair with infected skin scales or hair stubs – hyphae grow into stratum corneum sporadic cases of ringworm are acquired from cats or dogs (M. canis) epidemics of tinea capitis – due to use of shared barber shop clippers, transfer of infected hairs on seats, person – person contact control depends on cleanliness, sterilization of

instruments (using hot mineral oil), effective treatment of cases and reduced contact with infectious materials