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introduction to Dermatophytosis


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Dermatophytes

These are hyaline molds that derive nutrients by breaking down keratin, a protein that is the major component of skin, hair, and nails. They are the causative agents of dermatophytosis.

Dermatophytosis (syn: ringworm, tinea) is a communicable skin disease affecting the outer layer of the epidermis, the stratum corneum, and also may invade the hair and nails.

These organisms, called dermatophytes, are the pathogenic members of the keratinophilic (keratin digesting) soil fungi. The etiological agents of dermatophytoses can be classified into three anamorphic genera: ❑Trichophyton, Microsporum, and Epidermophyton.

Based on host preference and natural habitat, dermatophytes have been grouped into three categories
Microsporum and Trichophyton are human and animal pathogens. Epidermophyton is a human pathogen.

• Anthropophilic dermatophytes are mainly found in humans and are very seldom transmitted to animals.
Geophilic these species inhabit soil, where they are associated with decomposing hair, feathers and other keratin sources. They infect both humans and animals
• Zoophilic species are pathogens of animals; however, transmission from animals to humans does occur.
Dermatophytes

Dermatophytes grow best in warm and humid environments and are, therefore, more common in tropical and subtropical regions
• Microsporum - infections on skin and hair
• Epidermophyton - infections on skin and nails
• Trichophyton - infections on skin, hair, and nails.
• Epidermophyton- E. floccosum
• Microsporum- M.canis
• M. gypseum
• Trichophyton-T. rubrum
• T. mentagrophytes
• T. verrucosum
• T.violaceum

Transmission

• Infection occurs by contact with arthrospores (asexual spores formed in the hyphae of the parasitic stage) or conidia (sexual or asexual spores formed in the “free living” environmental stage).
• Infection usually begins in a growing hair or the stratum corneum of the skin. Dermatophytes do not generally invade resting hairs, since the essential nutrients they need for growth are absent or limited. Hyphae spread in the hairs and keratinized skin, eventually developing infectious arthrospores.
• Transmission between hosts usually occurs by direct contact with a symptomatic or asymptomatic host, or direct or airborne contact with its hairs or skin scales. Infective spores in hair and dermal scales can remain viable for several months environment.
• Geophilic dermatophytes are usually acquired directly from the soil rather than from another host

Routes of •Close human contact
transmission •Sharing combs, brushes, towels
Animal-to-humancontact

what is Pathogenesis

• The ability of certain fungi to adhere to particular host arises from numerous mechanisms and host factors, including the ability to adapt to the human body.
• Natural infection is acquired by the deposition of viable arthrospores or hyphae on the surface of the susceptible individual. After the inoculation in the host skin, suitable conditions favor the infection to progress through the following stages:
• Adherence
• Penetration

Adherence & Penetration

• After overcoming obstacles (ultraviolet light, temperature, and moisture variation) and competing with the normal flora, the arthroconidia (infectious element) adhere to the keratinized tissue. The germination of arthroconidia and hyphal growth adherence proceeds radially in multiple directions.
• Dermatophytes have an arsenal of proteases aimed at the digestion of the keratin network into amino acids. Once established, the spores must germinate and penetrate the stratum corneum.
Tinea capitis

Tinea capitis, most often seen in children, is a dermatophyte infection of the hair and scalp. Tinea capitis begins with a small papule, which spreads to form scaly, irregular or well-demarcated areas of alopecia.

Both anthropophilic and zoophilic dermatophytes can cause tinea capitis. It is most often caused by the anthropophilic dermatophyte T. tonsurans. Most common agents: M.
audouinii, M. canis.

Other agents: M. ferrugineum, M. gypseum, M. nanum, M. persicolor, T. megninii, T. mentagrophytes, T. schoenleinii, T. soudanense, T. verrucosum, T. violaceum.

Tinea capitis is classified into endothrix, ectothrix, or favus, according to microscopic pattern of invasion.
Endothrix

In the endothrix form, hyphae grow down the follicle and penetrate the hair shaft, then grow completely within the hair shaft. Composed of fungal anthoconidia and hyphae without cuticle destruction. This form is caused predominantly by T. tonsurans and T. violaceum.

This produces relatively noninflammatory patches of alopecia with fine scale, classically studded with broken-off, swollen hair stubs, resulting in a ‘black dot’ appearance. The hair shaft is filled with fungal branches (hyphae) and spores (arthroconidia). Patches may be multiple

Ectothrix

In the ectothrix form, the hyphae invade the hair shaft at mid follicle. Afterwards, hyphae grow out of the follicle covering the hair surface. This form is caused by M. canis,
M. audouinii, Microsporum ferrugineum, and Trichophyton verrucosum
Typically it produces characteristic fine scaling with patchy circular alopecia, dull grey in color due to arthrospores coating the affected hairs. The fungal branches (hyphae) and spores (arthroconidia) cover the outside of the hair. Inflammation may be minimal with anthropophilic fungi (e.g. M. audouinii, M. ferrugineum); however, zoophilic or geophilic species (e.g. M. canis, M. gypseum) typically demonstrate more intense inflammatory response.

Grey patchy alopecia

Favus

The hyphae grow parallel to the hair shaft in favus form then degenerate, leaving long tunnels within the hair shaft. Favus form is caused by Trichophyton schoenleinii and is characterized by yellow crust around the hair shafts and can result in permanent scarring alopecia
The favic type of infection is caused by the anthropophilic dermatophyte T. schoenleinii. The affected hairs are less damaged than in the other types, and may continue to grow to considerable lengths. Air spaces in the hair shafts are characteristic and fungal hyphae form large clusters at the base of hairs where they enter the follicle at the level of the epidermis.
The main clinical manifestations of favus are the formation of crusted, inflamed patches on the scalp, with permanent hair loss due to follicular scarring. ❑The scalp itches
The crusts (scutula) develop around the follicular openings and can fuse to cover large areas of the scalp.
Favus characterised by yellow cup-shaped crusts (scutula) that group together in patches like a piece of honeycomb.

Clinical features

The clinical appearance of ringworm of the scalp is variable, depending on the type of hair invasion, the level of host resistance and the degree of inflammatory host response.
Most affected patients are children 6 months to 10–12 years of age. Tinea capitis can sometimes occur in adults and in this case is usually caused by anthropophilic fungi.
The pattern varies from a few, broken-off hairs with little scaling, detectable only on careful inspection, to a severe, painful, inflammatory mass or kerion covering most of the scalp. Itching is variable. In all types, the characteristic features are partial hair loss with some degree of inflammation.
Kerion- a painful, inflammatory mass in which those hairs that remain are loose. Follicles also discharge pus. It may mimic a bacterial folliculitis or an abscess of the scalp.

• Inflammatory mass (kerion) covering most of the scalp
Tinea Pedis

Tinea pedis (Athlete’s foot) is an infection of the foot, characterized by fissures, scales and maceration in the toe web, or scaling of the soles and lateral surfaces of the feet. Erythema, vesicles, pustules and bullae may also be present. It is usually caused by anthropophilic dermatophytes. Most common agents*: T. rubrum, T. mentagrophytes var interdigitale, E. floccosum. Other agents: M. persicolor, T. raubitschekii, T. violaceum.
There are four presentations of tinea pedis, namely interdigital tinea pedis, frequently referred to as athlete’s foot, moccasin (chronic hyperkeratotic) tinea pedis, inflammatory or vesicular tinea pedis, and ulcerative tinea pedis.

Interdigital tinea pedis

• T. rubrum is the most common agent followed by anthropophilic T. interdigitale
• This type of tinea pedis usually presents with interdigital erythema, scaling, maceration and fissuring.
• The lesions can be found between the fourth and fifth toes. The dorsal surface of the foot is generally unaffected, but adjacent plantar areas may be involved The lesions can be found between the fourth and fifth toes. The dorsal surface of the foot is generally unaffected, but adjacent plantar areas may be involved
• Complications: Hyperkeratosis, leukokeratosis or erosions
• Symptoms: Itching, burning and malodour

Moccasin (chronic hyperkeratotic) tinea pedis

Primarily caused by T. rubrum, the infection typically presents with chronic plantar erythema ranging from slight scaling to diffuse hyperkeratosis
The infection pattern typically presents with dry hyperkeratotic scaling, which primarily affects the entire plantar surface. It then extends to the lateral foot. On the dorsal foot surface, the foot is usually clear.
Complications: Due to the constant scratching of the feet, Tinea manuum (fungal infection of the hands) may develop as a result.
Symptoms: The condition may be asymptomatic but may also present with mild erythema, thick hyperkeratotic scales with fissures, moderate-tosevere pruritus, and painful fissures while walking

Inflammatory or vesicular tinea pedis

• Anthropophilic T. interdigitale is the primary causative agent.
• The observed characteristics of vesicular tinea pedis include hard, tense vesicles, bullae and pustules on the in-step or mid-anterior plantar surface of the foot
• The bullae appear in round, polycyclic, herpes-like or gradually spreading clusters with an erythematous base and are localised to the arches of the feet, sides of the feet, toes and sub-digital creases. New vesicles develop on the periphery, with fissures often appearing in the cleft and sub-digital creases.
• Complications: Cellulitis, adenopathy and lymphangitis
• Symptoms: Severe itching accompanied by burning and pain. The intensity of inflammation varies amongst individuals and may make walking difficult.
Ulcerative tinea pedis
Most commonly caused by Anthropophilic T. interdigitale, this form of tinea pedis usually presents with rapidly spreading vesiculopustular lesions, ulcers and erosions. Bacterial infections are usually present as a secondary infection.
This clinical form usually begins in the third and fourth interdigital spaces. It then spreads to the lateral dorsum and the plantar surface. In severe cases, it may even extend to large areas whereby the entire sole can even be sloughed.

Complications: Cellulitis, lymphangitis, fever and malaise
Symptoms: Ulcers, pain of varying degrees and itching

Dermatophytid - an "id" allergic reaction

• Allergic reactions are sometimes associated with tinea pedis and this reaction is called dermatophytid - "id" reaction. This occurs at a distant site from primary infection.
• An id reaction is a secondary immunologic host response that follows a primary eczematous process, such as tinea infection, especially tinea pedis. Clinically, patients present with widespread symmetrical eruptions of small, erythematous papules and vesicles often on the forearms and hands; however, they can occur anywhere on the body.
• The disorder usually appears acutely over a few days and the acute eruption may subside spontaneously in a few weeks if the primary dermatitis is treated.
• Clinical Features:
• The patient must have an identifiable primary dermatophyte infection
• The id reaction consists of erythematous eczematous papules or small plaques
• Id reactions are often but not always intensely pruritic
• Generally, id reactions have a tendency to be more severe near to the primary process and decrease in intensity with distance from the primary process, but there are exceptions. For example, patients with tinea pedis may have id reactions that consist of scaling of the palms, well away from the feet.
“id” reaction continued

The eruptions are typically itchy. They may appear as:

- Small, fluid-filled spots (on the hands or feet)
- Solid bumps
- Red, raised patches
- Deep, raised, bruise like areas on the shins
- Red, raised swellings (hives)

Clusters of papules on the back of the hand Clusters of papules on the knees
Tinea Corporis

Tinea corporis, or ringworm, occurs on the trunk, extremities and face. It is characterized by single or multiple scaly annular lesions with a slightly elevated, scaly and or erythematous edge, sharp margin and central clearing.
Follicular papules, pustules or vesicles may be found on the borders of the lesion. Lesions may be variably pruritic. Both zoophilic and anthropophilic dermatophytes are common in children, and on the neck and wrists of adults in contact with the child.
In other adults, tinea corporis is often the result of chronic infection with T. rubrum, an anthropophilic dermatophyte. In many people, untreated tinea corporis resolves within a few months, particularly if it is caused by a zoophilic or geophilic organism. Most common agents*: T. rubrum, M. canis, M. tonsurans, T. verrucosum. Other agents: E.
floccosum, M. audouinii, M. gypseum, M. nanum, M. persicolor, T. equinum, T. mentagrophytes, T. raubitschekii, T. schoenleinii, T. violaceum

Tinea cruris
Tinea cruris (‘jock itch’) is an extremely common superficial fungal infection of the groin and upper thighs. It is seen primarily in male adolescents and adults, and occurs less commonly in females. Tinea cruris is most symptomatic in hot, humid weather and is most frequently noted in obese individuals or those subject to vigorous physical activity and chafing. Tight-fitting clothing such as athletic supporters, jockey shorts, wet bathing suits, and panty hose may contribute to this condition as well.
The three most common dermatophytes to result in tinea cruris are E. floccosum, T. rubrum, and T. mentagrophytes.
Tinea cruris presents as erythematous plaques with an elevated border of scaling, pustules, or vesicles. It involves the intertriginous folds near the scrotum, the upper inner thighs and occasionally the perianal regions, buttocks and abdomen.

LABORATORY DIAGNOSIS

Required samples:
-Skin scrapping
-Nail Scraping -Hair plucking

Microscopy
Culture

Treatment

• Treatment consists of topical or systemic antifungal drugs with antidermatophyte activity.
• Most cutaneous dermatophyte infections limited to the epidermis can be managed with topical antifungal therapy. Example of an agent effective for dermatophyte infections include azoles which includes clotrimazole and ketoconazole.
• Oral treatment with agents such as itraconazole and fluconazole is used for extensive infections, infections that are refractory to topical therapy, or infections extending into follicles or the dermis (eg, tinea capitis, tinea barbae) or involving nails.
THE END