Dermatophytes: Fungal Infections

• Dermatophyte infections are caused by a class of fungi that invade and degrade keratinized tissues like hair, skin, and nails
• Dermatophytes belong to the Ascomycota phylum, Eurotiomycetes class, Onygenales order, and Arthrodermataceae family
• The seven accepted genera of dermatophytes are Trichophyton, Epidermophyton, Nannizzia, Paraphyton, Lophophyton, Microsporum, and Arthroderma

Categories of Dermatophytes

• Anthropophilic dermatophytes are mainly found in humans and are very rarely transmitted to animals
• Geophilic species live in soil, they are associated with decomposing hair, feathers and infect both humans and animals
• Zoophilic species are animal pathogens that can be transmitted from animals to humans

Anthropophilic Dermatophytes

• Dermatophytes that preferentially infect humans are classified as anthropophilic
• Approximately 10 dermatophyte species in the Trichophyton and Epidermophyton genera are considered anthropophilic
• Trichophyton rubrum, Trichophyton interdigitale, and Epidermophyton floccosum cause the majority of infections

Zoophilic Dermatophytes

• Zoophilic dermatophyte species evolved to live on non-human animals
• Infections in humans are mostly caused by M. canis, T. mentagrophytes, and T. verrucosum
• Cats are the primary host for M. canis

Geophilic Dermatophytes

• Geophilic dermatophytes mainly reside in soil and keratinous debris shed from animals, and rarely cause infections
• Nannizzia gypsea (Microsporum gypseum) is the most common species to cause infection in humans and animals

Routes of Transmission

• Human-to-human transmission occurs through close contact or sharing personal items like combs and towels

Transmission Details

• Transmission of infection occurs through arthrospores and conidia.
• Arthrospores form in the hyphae of the parasitic stage
• Conidia can be sexual or asexual spores formed in the "free living" environmental stage
• Infection usually begins in growing hair or the stratum corneum of the skin
• Dermatophytes generally do not invade resting hairs because they require essential nutrients for growth
• Hyphae spread and develop infectious arthrospores
• Transmission typically occurs from direct contact with a symptomatic or asymptomatic host, or airborne contact with hair or skin scales
• Infective spores in hair and dermal scales can remain viable for several months

Initiation of Dermatophyte Infections

• Dermatophytes are free-living, but can cause infections in humans/animals under certain conditions
• Dermatophytes are molds that are septate, hyaline, and filamentous
• Dermatophytes produce spores (conidia) and comprise mainly of mycelium

Initiation Process

• Arthroconidia adheres to the epidermis within 2-6 hours of contact, initiating germination in the stratum corneum
• Germinating arthroconidia develop germ tubes to penetrate the epidermis
• As the dermatophytes degrade keratin, the pH at the infection site becomes more basic, encouraging fungal proteases
• Fungal hyphae continues to grow and begin producing arthroconidia within 7 days of infection, enabling spread

Pathogenesis - Adherence

• Dermatophytes produce asexual spores called arthroconidia, which attach to tissue surfaces
• Trichophyton rubrum uses carbohydrate-specific adhesions on the spore surface to adhere to epithelial cells
• T. mentagrophytes develops fibrillar projections that connect fungal arthroconidia to keratinocytes
• Arthroconidium germinates into hypha to penetrate the stratum corneum in 2-6 hours

Pathogenesis - Penetration

• Dermatophytes need to obtain nutrients for survival after adherence
• Complex compounds are degraded via secreted enzymes such as proteases, lipases, elastases, collagenases, phosphatases, and esterases
• Keratinases degrade the keratin present in the host tissues into oligopeptides or amino acids
• Proteolytic enzymes degrade the proteins of the skin, aiding in the penetration of the stratum corneum

Types of Dermatophytosis

• Tinea capitis: Ringworm infection of the head, scalp, eyebrows, and eyelashes
• Tinea pedis: Ringworm infection of the foot also known as Athlete's foot
• Tinea cruris: Ringworm infection of the groin (jock itch)
• Tinea barbae: Ringworm infection of the beard
• Tinea corporis: Ringworm infection of the body (smooth skin)
• Tinea manuum: Ringworm infection of the hands
• Tinea unguium: Ringworm infection of the nails
• Tinea faciei: Infection of the face

Tinea Capitis

• Tinea capitis is a dermatophyte infection of the hair and scalp that begins with a small papule
• It typically spreads to form scaly, irregular/well-demarcated areas of alopecia and is most often seen in children
• T. tonsurans is the most common anthropophilic dermatophyte
• Both anthropophilic and zoophilic dermatophytes can cause it

Tinea Capitis - Endothrix

• In the endothrix form, hyphae grow down the follicle and penetrate the hair shaft, then grow completely within
• Composed of fungal arthroconidia and hyphae without cuticle destruction, often caused by T. tonsurans and T. violaceum
• Scalp produces relatively noninflammatory alopecia patches with fine scale
• Hair is classically studded with broken-off, swollen hair stubs, resulting in a 'black dot' appearance.

Tinea Capitis - Ectothrix

• Hyphae invade the hair shaft at mid follicle and grow out of the follicle, covering the hair surface
• Caused by M. canis, M. audouinii, Microsporum ferrugineum, and Trichophyton verrucosum
• Produces fine scaling with patchy circular alopecia, and dull grey coloring from arthrospores on affected hairs
• May be minimal inflammation with anthropophilic fungi, zoophilic and geophilic species demonstrate a more intense inflammatory response

Tinea Capitis - Favus

• Hyphae grow parallel to the hair shaft then degenerate, leaving tunnels
• Caused by Trichophyton schoenleinii and is characterized by yellow crust around the hair shafts, which can result in permanent scarring alopecia
• Infections are caused by the anthropophilic dermatophyte T. schoenleinii
• Hairs are less damaged and continue to grow longer while air spaces become characteristics, and fungal hyphae form large clusters
• The main manifestation is crusted, inflamed patches, scalp itching, and crusts (scutula) that develop around the scalp

Tinea Capitis - Clinical Features

• Clinical appearance and ringworm are variable
• Clinical appearance is dependent on the type of hair invasion, host resistance, and degree of inflammatory host response
• Most affected patients are children aged 6 months to 12 years, sometimes occurring in adults, in which case it is caused by anthropophilic fungi
• Patterns vary, but characteristics feature hair loss with some degree of inflammation

Tinea Pedis

• Tinea pedis (athlete's foot) shows fissures, scales/maceration in the toe web, and the soles/lateral are scaled
• Erythema, vesicles, pustules, and bullae may also be present
• Anthropophilic dermatophytes commonly cause tinea pedis, most commonly: T. rubrum, T. mentagrophytes var interdigitale, and E. floccosum

Tinea Pedis Presentations

• Interdigital tinea pedis (athlete’s foot)
• Moccasin (chronic hyperkeratotic) tinea pedis
• Inflammatory or vesicular tinea pedis
• Ulcerative tinea pedis

Tinea Pedis - Interdigital

• T. rubrum is the most common agent
• Presents with erythema, scaling, maceration, and fissuring

Tinea Pedis - Moccasin

• Caused primarily by T. rubrum
• Symptoms: chronic plantar erythema, dry hyperkeratotic scaling, mild erythema, thick hyperkeratotic scales with fissures, moderate-to-severe pruritus, and walking fissures.
• Infection pattern typically presents with dry scaling
• Lateral extends to the foot

Tinea Pedis - Inflammatory and Vesicular

• Anthropophilic T. interdigitale agent that presents tense vesicles, bullae and pustules on the in-step/mid-anterior plantar surface
• The Bullae present as round, polycyclic, herpes-like, spreading clusters with an erythematous base that may lead to Cellulitis
• The most common symptom is severe itching and intense burning with inflammation, and pain

Tinea Pedis -Ulcerative

• Anthropophilic T. interdigitale commonly causes it with rapidly spreading lesions, ulcers, and erosions that may induce bacterial infections
• Clinical forms start in the third and fourth interdigital spaces then spread to the lateral dorsum with erythema, scaling, maceration, and fissuring
• Ulcers are a common sign of this disease, and may feel varying degres of itchiness

Treatment - Topical Antifungals

• Azoles: Clotrimazole, Miconazole
• Allylamines: Terbinafine, Naftifine
• Ciclopirox: Broad-spectrum antifungal
• Tolnaftate: Over-the-counter option
• Apply twice daily, with a duration of 2-4 weeks

Treatment - Oral Antifungals

• (For severe or resistant cases)
• Terbinafine (250 mg daily for 2-4 weeks)
• Itraconazole (200 mg daily for 1 week or 100 mg daily for 4 weeks)
• Fluconazole (150-200 mg weekly for 2-6 weeks)

Treatment - Adjunctive Measures

• Keep feet dry
• Avoid occlusive footwear
• Disinfect shoes and socks (antifungal sprays, UV shoe sanitizers)
• Use separate towels

Tinea Corporis (Ringworm)

• Ringworm occurs on the trunk, extremities, and face. It is defined by single or multiple scaly annular lesions, has variably pruritic borders and is caused by both zoophilic and anthropophilic dermatophytes
• More prevalent in children/adults that are in the neck or hands, often a result of chronic infections through T. rubrum
• Follicular papules, pustules, or vesicles can be found on the borders of the lesion and has a sharp margin

Tinea Corporis - Management

• Clotrimazole: 1% cream/ointment/solution applied topically twice daily
• Ketoconazole: 2% cream/shampoo/gel/foam applied once daily
• Miconazole: 2% cream/ointment/solution/lotion/powder applied twice daily
• Naftifine: 1% cream applied once daily or apply 1 to 2% gel twice daily
• Terbinafine: Apply this cream once or twice daily
• Oral therapy is necessary in widespread infections, terbinafine and itraconazole usually clear the condition in 2-3 weeks

Tinea Cruris (Jock Itch)

• Tinea cruris is an extremely common infection around the thigh, often seen in adolescents and males due to sensitivity around hot, humid weather and vigorous activites/chafing

• Tight-fitting clothing that athletes or swimmers wear may contribute to this condition

• Three common dematophytes that can result in this condition are E. floccosum, T. rubrum, and T. Mentagrophytes

• It presents elevated Erythematous plaques around the scrotum, and upper- inner thighs

• The redness scales with active margins

• Lesions of the disease can vary in colour and may cause redness

• Also present are lichenification and slight scaling

Allergic Reaction

• A patient with dermatophytois may become hypersensitive to components products, vesicles may develop and skin tests may positive

Dermatophytid - an "id" allergic reaction

• The allergic reactions are sometimes associated with with tinea pedis, occurring on distant locations
• Occurs as the effect causes a secondary immunologic host that causes the reaction, due to the sensitive nature
• Over a matter of weeks or days, the disorder may improve spontaneously, or erupt during primary dermatitis

Dermatophytid - Clinical Features

• The patient must have a dermatophyte infection to be identifed
• Contains a eczematous and pruritic id reaction
• Reactions are often and but decrease in intensity due to certain excemptions

Dermatophytid - Symptoms

• The eruptions are typically itchy and 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)

Specimens

• Consists of scrapings from the skin and nails plus hair from involved areas

Wood's Lamp for Diagnoses

• Tool uses ultraviolet light (wavelength ranges between 320-400 mm) to detect fluorescence from active dermatophyte infection
• The UV lights may flouresc M. canis, M. audouinii, M. ferrugineum,, N. gypsea, and Trichophyton schoenleinii

Microscopic Examination

• Clinical samples are enhanced with various stains
• Potassium hydroxide (KOH) detects presence of fungi, but cannot differentiate species
• Lactophenol cotton blue stains chitin in fungal cell walls to enhance structures

Diagnoses thru Culture:

• Considered “gold standard” for diagnosing dermatophytosis from a clinical sample grown
• Dextrose agar containing cycloheximide and chloramphenicol suppress mold and bacterial growth
• Species are determined via colonial morpholgy