Dermatophytoses

Dr. Pendru Raghunath ReddyAssistant Professor of MicrobiologyDr. VRK Women’s Medical College

Dermatophytoses or cutaneous mycoses are diseases of the skin, hair and nail

Generally called ringworm infections and tinea

These infections are caused by a homogenous group of closely related fungi known as dermatophytes

These dermatophytes infect only superficial keratinised structures such as skin, hair and nail but not deeper tissues

The most important dermatophytes that cause infection in humans are classified into three genera

Trichophyton - infections on skin, hair, and nails.

Microsporum - infections on skin and hair (not the cause of TINEA UNGUIUM)

Epidermophyton - infections on skin and nails (not the cause of TINEA CAPITIS)

The dermatophytes on the basis of their natural habitat andhost preferences can be classified into following groups

1. Anthropophilic species

2. Zoophilic species

3. Geophilic species

Anthropophilic

Associated with humans only

Person -to-person transmission through contaminated objects (fallen hairs, desquamated epithelium, combs, hat, towel etc.)

Examples: Trichophyton rubrum, Microsporum audouinii and Epidermophyton floccosum

Zoophilic

Associated with animals

Direct transmission to humans by close contact with domestic animals (cat and dog) and occasionally wild animals

Examples: Trichophyton violaceum and Microsporum canis

Geophilic

These are saprophytic fungi found in soil or in dead organic substances

They occasionally cause infection in humans and animals

Examples: Microsporum gypseum and Trichophyton ajelloi

Dermatophytes usually grow only on keratinised skin and its appendages and do not penetrate the living tissue

In some infected persons, hypersensitivity to fungus antigen may cause secondary eruptions such as vesicles on the finger

This reaction is known as dermatophytid (Id) reaction

This reaction occurs as a result of hypersensitivity response to circulating fungal antigen, and these lesions do not contain any fungal hyphae

Dermatophytid (Id) reaction

Clinical features

The skin infections caused by dermatophytes are chronic infections of the skin often found in the warm humid areas of the body

Typical ringworm lesions are circular , dry, erythematous, scaly and itchy which have an inflamed border containing papules and vesicles surrounding a clear area of relatively normal skin

These lesions are associated with variable degrees of scaling and inflammation

Nails are thickened, deformed, friable, discolored, subungual debris accumulation

Dermatophytoses clinical classification

• Infection is named according to the anatomic location involved:

a. Tinea barbae e. Tinea pedis (Athlete’s foot)

b. Tinea corporis f. Tinea manuumc. Tinea capitis g. Tinea unguiumd. Tinea cruris

(Jock itch)

Transmission

• Close human contact

• Sharing clothes, combs, brushes, towels, bedsheets... (Indirect)

• Animal-to-human contact (Zoophilic)

Tinea capitis

This is the infection of the shaft of scalp hairs and presents as the following clinical types

a) Inflammatory – Kerion, favusb) Non-inflammatory – Black dot, Ectothrix and Endothrix The infected hairs in tinea capitis appear dull and grey

The base of hair shaft as well as hair follicles is involved

There is breakage of hair at follicular orifice which creates patches of alopecia with black dots of broken hairs

Tinea capitis

Ectothrix

The arthrospores appear as mosaic sheath around hair or as chains on surface of hair shaft

The cuticle of hair remains intact

Hyphae invade hair shafts at mid follicle and as hair grows out of follicle, hyphae burst out of shaft and cover hair surface with mass of small arthrospores

Caused by T. mentagrophytes, M. canis, M. audouinii, M. gypseum and T. verrucosum

EndothrixHyphae form arthrospores within hair shaft, which is severely weakened

Cuticle of hair is usually destroyed

The arthrospores are 3-4 µm in diameter and are observed in chains filling inside shortened hair stubs

Caused by T. schoenleinii, T. tonsurans and T. violaceum

T. rubrum cause both ectothrix as well as endothrix infections

Tinea corporis

This is disease of glabrous (non-hairy) skin of body and may result from extension of infection from scalp, groin or beard

Characterised by erythematous scaly lesions, annular, sharply marginated plaques with raised border which may be single, multiple or confluent

Tinea corporis

Tinea Pedis

This is the infection of plantar aspect of foot, toes and interdigital web spaces

It is frequently seen among individuals wearing shoes for long hours and popularly known as Athlete’s Foot

In toe webs, scaling, fissuring, maceration and erythema may be associated with an itching or burning sensation

Due to maceration and peeling, cracks appear which are prone to secondary bacterial infections

When infection becomes chronic, sole becomes hyperkeratotic and is often covered with fine scales

Tinea Pedis

Tinea Barbae

Infection of beard and moustache areas of face with invasion of coarse hairs

Also called as barber’s itch

There are erythematous patches on face which show scaling

Tinea Barbae

Tinea Faciei

Dermatophytic infection of skin that occurs on non-bearded regions of face

Tinea Cruris

Dermatophytic infection of groin

Involves perineum, scrotum and perianal area and may spread to inner third of buttock and occasionally to thigh

The appearance of Tinea Cruris can be seen in other intertriginous areas such as axilla and around umblicus of obese patients

Tinea Manuum

Dermatophyte infection of skin of palmar aspect of hands

The most common clinical manifestation is diffuse hyperkeratosis of palms and fingers

Tinea Unguium

Dermatophyte infection of nail plates and is largely a disease of adults

It begins under leading free edge of nail plate or along lateral nail fold and may continue until entire nail plate and nail bed are infected

There is accumulation of subungual debris in an opaque, chalky or yellowish thickened nail

Tinea Unguium

Laboratory diagnosis

Specimens

Scrapings of the skin and nail as well as short lengths of hair plucked from the scalp. Scrapings are taken from the edges of ringworm lesions

Direct microscopic examination

KOH wetmount

Branching hyaline septate (non-pigmented) hyphae is considered positive for fungi; spores may also be seen

Wood’s lamp

In suspected Tinea capitis, plucked hair is examined by using wood’s lamp

Infected hair will be fluorescent (yellow green)

Culture

Species identification is possible only by culture examination

Sabouraud’s dextrose agar containing chloramphenicol and cycloheximide

The plates incubated aerobically at 25-300C for upto 21 days

Identification of dermatophytes in the laboratory is by examing the macroscopic characteristics of the fungal colonies (rate of growth, texture, colour on the observe and reverse)

Microscopic examination

Trichophyton

Microconidia are abundant and arranged in clusters along the hyphae

Macroconidia are relatively scanty generally elongated, with blunt ends and have distinctive shapes in different species

Some species possess special hyphal characters such as spiral hyphae, raquet mycelium and favic chandeliers

Microsporum

Microconidia are relatively scanty and not distinctive

Macroconidia, the predominant spore form, are large, multicellular, spindle shaped structures, borne singly on the ends of hyphae

Microsporum species infect the hair and skin but usually not the nails

Epidermophyton

Colonies are powdery and greenish yellow

Microconidia are absent

Macroconidia are multicellular, pear-shaped and typically arranged in clusters

Epidermophyton attacks the skin and nails but not the hair

Epidermophyton floccosum

Treatment

This is by using topical preparations (ointments or gels) containing azoles (miconazole, clotrimazole, econazole) or terbinafine

Oral preparations of griseofulvin, azoles (ketoconazole, itraconazole) or terbinafine