Dermatophytes PDF

# Dermatophytes Dr. Rubaiya Binte Kabir M.Phil : Part - 1 ## General Characteristics - Dermatophytes are cutaneous fungi which infect only the keratinized tissues by liberating keratinase enzyme which helps them to invade into keratinized tissue like stratum corneum layer of skin, hair and na...

# Dermatophytes Dr. Rubaiya Binte Kabir M.Phil : Part - 1 ## General Characteristics - Dermatophytes are cutaneous fungi which infect only the keratinized tissues by liberating keratinase enzyme which helps them to invade into keratinized tissue like stratum corneum layer of skin, hair and nail. - It is a group of about 40 related fungi that belong to three genra: - Microsporum - Trichophyton - Epidermophyton. - They are restricted to non-viable skin because most are unable to grow at 37°C or in the presence of serum. - Many species have particular keratinase, elastase and other enzymes which make them host specific. - Several are capable of sexual reproduction - produce ascospore. Thus belongs to genus Arthroderma. ## Ascospore (sexual spores) - A microscopic image of an ascospore with 8 spored asci and ascospores. ## In skin, they produce hyaline, septate, branching hyphae, or chains of arthoconidia. - A microscopic image of arthroconidia, an asexual form. - E. floccosum is the only pathogen in this genus which produces macroconidia. ## Other characteristics - They are highly contagious and frequently transmitted by exposure to shed skin scale, nails, hairs containing hyphae and conidia. - They remain viable for long periods on fomites. ## Classification - According to shape and site of infection: - **Microsporum**: spindle shaped; infect skin and hair. - M. canis - M. gypseum - M. gallinae - M. nanum. - **Trichophyton**: pencil shaped; infect skin, nail, hair. - T. rubrum - T. tonsurans - T. mentagrophytes. - **Epidermophyton**: club shaped; infect skin and nail. - E. floccosum. - According to habitat: - **Antropophilic**: habitat in human body. - some Trichophyton species - E. floccosum. - **Geophilic**: usually habitat in soil. - M. gypseum. - **Zoophilic**: usually habitat in animal. - M. canis (dogs and cats) - M. gallinae (fowl) - M. nanum (pigs) - T. equinum (horses) - T. verrucosum (cattle). ## Immunity - Trichophytid reaction: trichophytin is a crude antigen preparation that can be used to detect immediate or delayed type hypersensitivity. - chronic, noninflammatory dermatophyte infection - poor cell medicated immune response to dermatophyte antigen. - Immediate type hypersensitivity with elevated IgE. - Allergic reaction - dermatophytid (usually vesicle and often in hand) - Trichophytid reaction : markedly positive - A photo of a hand with a dermatophytid reaction. ## Clinical findings - Dermatophytosis is classified according to site of involvement: - **Tinea capitis**: infection in scalp and hair. - **Tinea barbae**: infection in beard area. - **Tinea corporis**: infection in the trunk. - **Tinea cruris (jock itch)**: infection in groin/ inguinal region. - **Tinea manum**: infection in hand. - **Tinea unguium (onychomycosis)**: infection in nail - **Tinea pedis (athlete's foot)**: infection in foot. ## Tinea Capitis - Dermatophytosis or ringworm of the scalp and hair is called Tinea capitis. - Caused by Trichophyton or Microsporum. - **Pathogenesis**: - Hyphal invasion of the skin of scalp - Subsequent spread down the keratinized wall of hair follicle - Infection begins just above hair follicle, grow downwards on noninvolving area as the hair grows upwards. - Production of dull grey, circular patches of alopecia, scaling and itching. ## As the hair grows out of the follicle - 1. **Microsporum**: Hypae produce chain of spores forming sheath around the hair shaft - ectothrix. 2. **Trichophyton**: hypae produce spores within the hair shaft - endothrix. - Hair become weakened; typically break easily at the follicle opening. - A diagram of hair shafts with ectothrix and endothrix. 3. **Zoophilic species**: induce combined inflammatory and hypersensitivity reaction - kerion. - A photo of a scalp with a kerion. 4. **Trochophyton schoenleinii**: acute inflammatory reaction of hair follicle leading to formation of scutula (crust) - favus. - A photo of a scalp with favus. ## Tinea Barbae - Highly inflammatory reaction resembling pyogenic infection. - A photo of a beard with Tinea Barbae. ## Tinea Corporis - Annular lesion of ringworm with a clearing, scaly center surrounded by a red advancing border that may be dry or vescicle. - A photo of a Tinea Corporis lesion. - **Pathogenesis**: - Fungal metabolites, enzymes, antigens diffuse through the viable layers of the epidermis - Erythema, vesicle formation, pruritus - Lesion expand centrifugally and active hyphal growth at periphery. - A photo of a lesion expanding centrifugally. ## Tinea Cruris - Mostly occurs in men. - Dry, itchy lesions often start at the scrotum and spread to the groin. ## Tinea Manus - Dry, scaly lesion may involve one or both hands, single finger, or two or more fingers. - A photo of a hand with Tinea Manus. ## Tinea Unguium / Onychomycosis - May affect toe nails or finger nails, but toe nail infection is particularly common which follows tinea pedis. - Caused by: Trichophyton and Epidermophyton. - **Risk factors**: - Diminished blood supply. - Humid, moist environment. - Perspiring heavily. - Bare foot in dump places. - DM, immunosuppression. -**Pathogenesis**: - With hyphal invasion - Nails become yellow, brittle, thickened and crumbly. - A photo of an infected toenail. ## Tinea Pedis / Athlete's foot - Chronic infection of toe webs. May be vesicle, ulcerative and moccasin types, hyperkeratosis of the sole. - Two photos of feet with Tinea Pedis. ## Coarse of disease - Itching between toes. - Development of small vesicles. - Rupture of vesicle and discharge of a thin fluid. - Skin of the toe webs become macerated and peels. - Cracks appear and secondary bacterial infection develops. - When become chronic, peeling and cracking are accompanied by pain and pruritus ## Laboratory diagnosis - **Sample**: - Skin scrapping. - Nail scrapping. - Hair plucking. - **Collection of samples**: - **Skin**: from the margin of the lesion, with the scalpel. - **Nail**: deeper part is collected and superficial part is discarded. - **Hair**: plucked by fine forceps. - **Wood's lamp test**: ectothrix of Microsporum species impart a greenish to silvery fluorescence when examined under Wood's light. - A photo of someone having a Wood's lamp test, with glowing infectious organisms. - **Microscopic examination**: - **KOH preparation of skin or nail**: branching hypae or chains of arthoconidia are seen. - A microscopic image of arthroconidia, KOH preparation. - **KOH preparation of hair**: ectothrix and endothrix are seen. - A microscopic image of ectothrix and endothrix. - **Culture**: - Incubation period : 1-3 weeks. - Incubation temparature : 25° С. - **Media used**: - Sabouraud's dextrose agar media. - Dermatophyte test media: Sabouraud's dextrose agar + cyclohexamide + chloramphenicol + phenol red. - Malt agar. - **Colony morphology**: - Various photos of different colonies in different media, for example T. rubrum, T.tonsurans, T. metagrophytes, Microsporum, Epidermophyton and Dermatophyte test media. - **Others**: - **PCR**: species specific identification. - **Nutritional test and growth at 37° C**. - **In vitro hair perforation**: placing an organism in a petri dish - water, yeast extract, hair. - An image of Trichophyton mentagrophytes with hair perforation. ## Treatment - Therapy consists of thorough removal of infected and dead epithelial structures and application of a topical antifungal drug.. 1. **Tinea capitis**: - oral Griseofulvin or terbinafin several weeks. - topical shampoo and miconazole cream several weeks. - alternative: itraconazole, ketokonazole. 2. **Others**: - oral itraconazole and terbinafine. - topical miconazole, tolnafate, clotrimazole 2-4 weeks. - troublesome cases: oral griseofulvin. 3. **Tinea unguium**: - orat itraconazole or terbinafine for months with surgical removal of the nail. - topical imidazole, luciconazole,.