Dermatophytosis

Mrs. Dalia Kamal Eldien

Msc in Microbiologylecture NO (5)

Objectives

Common characteristic of DermatophytesCommon species causing dermatophytosis, with

examples of the three genera EpidemiologyMorphologyClinical Signs Laboratory diagnosis

Introduction

Dermatophytosis is a common contagious disease (infectious disease), caused by fungi known as Dermatophytes.

Dermatophytes belong to Deuteromycetes class Dermatophytes a group of organisms that are able to

breakdown 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.

Some of Dermatophytes anthropophilic species, are adapted to humans, and are usually transmitted from person to person.

Others Zoophilic species, are adapted to animals, but can transmit to human.

A few Geophilic species, normally live in the environment, but occasionally act as parasites.

Etiology

Dermatophytes have 3 genera and many species

1-Microsporum: affect mainly skin and hair, common species include

o M. gypseumo M. caniso M. audouiniio M. nanum

2-Trichophyton : affect skin, hair & nail common species include.

o T. tonsuranso T. rubrumo T. violaceumo T. mentagrophytes o T. interdigitaleo T. soudanenseo T. schoenleinii

3- Epidermophyton. affect Skin & nail the only species iso E. floccosum

Epidemiology

Dermatophytes grow best in warm and humid

environments and 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

Morphology

Microsporum : produce many macro conidia (large, spindle shape& multicellular), and few microconidia

M. canis : have special spiculesM. audunii : produce special structure refer as

the pictenate body

Microsporum macroconidia

Microsporum canis macroconidia with spicules

Microsporum audouinii (pectinate bodies)

Morphology

Trichophyton: produce many micro conidia and few macroconidia (thin wall, cigar shape)

T. mentagrophytes : produce the spiral hyphaeT. schoenleinii : produce special structure refer as

the favic chandler

Trichophyton spp(examine the macro and micro conidia)

Trichophyton mentagrophytes(spiral hyphe)

Morphology

Epidemphyton: produce many macro(large, multi cellular & club shape) but no micro conidia

E.floccosum macroconidia

Transmission People and animals become infected by Dermatophytes

after contact with spores (conidia).

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

Clinical Signs

The symptoms of dermatophytosis vary, depending on the infecting organism, affected tissues (e.g., skin, hair or nails)

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.

Ringworm lesion

In haired areas, the hairs become brittle and areas of alopecia may appear.

Infection begins in a growing hair or in the stratum corneum, where threadlike hyphae develop from the infective arthrospores or fungal hyphal elements.

Hyphae can penetrate the hair shaft and weaken it, which, together with follicular inflammation, leads to a common clinical sign of patchy hair loss.

As the infection matures, clusters of arthro spores develop on the outer surface of infected hair shafts.

Broken hairs infected with spores are important sources for spread of the disease.

Tinea capitis

In humans, dermatophytoses are referred to as “Tinea” infections, and are named according to the area of the body involved.

Tinea capitis: most often seen in children, is a dermatophyte infection of the hair and scalp.

Tinea barbae in the beard and mustache area Tinea corporis occurs on the trunk and extremities Tinea cruris infection of the groin Tinea pedis (athlete’s foot) is an infection of the foot • Tinea unguium (or onchomycosis) is infection of the nails,

finger or toe• Tinea manuum hand and interdigetal space

Lab diagnosis

Specimen Before collect the specimen disinfect the area with 70%

alcohol with a pieces of gauze, using sterile blunted scalpel collect the specimen.

Skin scrapings should be taken from the edge of the lesion onto folded black paper.

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).

Wood's lamp examination

Direct microscopy Is a most important diagnostic step Using 20% KOH, in clean slide add one drop, to it take

part of specimen, passing 3 times over BB to and allowed to clear for 30 to 60 minutes to clear the keratin and expose the fugal elements , before examining on a light or phase contrast microscope.

Fluorescence microscopy, using calcofluor white or other stains, can also be used to visualize dermatophyte structures.

Under the microscope :- Skin: epithelia cell, if positive see the segmented hyphae,

Hyphae rounding up into arthrospore are diagnostic, but hyphae alone could be caused by other fungi, including contaminants.

• Nail: the same picture but the epithelial more flattened• Hair: arthrospore may be found outside the hair shaft i.e

between hair shaft& hair sheath, named as Ectothrix spore, or inside the hair shaft named as Endothrix.

KOH mount of infected skin scales (left) and nail material (right) showing typical

dermatophyte hyphae breaking up into arthroconidia.

Ectothrix spore(right)& Endothrixspore(left)

Culture: Fungal cultures, which identify the species of Dermatophyte,

also be necessary if the diagnosis is uncertain, or the infection is resistant to standard treatment.

Specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar containing cycloheximide (actidione) and chloramphnicol, incubated at 26-28C , Colonies appear in 5 days to 4 weeks, depending on the organism.

• Nails are scraped or minced into small pieces• Hair is cut into short segments• Each specimen is divided between at least two sets of

culture media

Potato dextrose agar: is a media useful for the production of pigment

Bromocresol purple milk solids glucose: is a differential media useful in the characterization of dermatophyte species. The growth pattern of restricted or profuse is determined by comparison to a tube of nutrient media such as SDA. Some species produce an alkaline reaction (change media to purple), others do not produce a pH change (leave the media a sky blue color). Hydrolysis of the milk solids results in a zone of clearing around the colony.

Colonies of T. mentagrophytes (left), T. rubrum (center) and T. violaceum (right) showing differential responses on Bromocresol Purple Milk Solids Glucose agar . T. mentagrophytes shows unrestricted growth with alkaline (purple) color change, T. rubrum shows restricted growth with no pH change, and T. violaceum produces weak growth accompanied by clearing of the milk solids and a purple color change.

Dermatophyte species can be identified by the colonial morphology.

Microscopical exam: to examine 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)

Mixed culture of T. violaceum and T. tonsurans from a case of endothrix Tinea

capitis 

M. gypseum culture

T.schoenleinii

M.canis

Some dermatophytes fluoresce when they are stimulated by the wavelengths of ultraviolet (UV) light in a Wood’s lamp.

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. 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.