Clinical Mycology Lec 3 PDF

Lec (3) Dermatophytosis Dr. Wifag Rabih INTRODUCTION Dermatophytosis is a common contagious disease ( Infectious disease caused by fungi known as dermatophytes. Generally called ringworm infections and tinea. Dermatophytes belong to Deuteromycetes class. Dermatophytes: a group of organisms that can...

Lec (3) Dermatophytosis Dr. Wifag Rabih INTRODUCTION Dermatophytosis is a common contagious disease ( Infectious disease caused by fungi known as dermatophytes. Generally called ringworm infections and tinea. Dermatophytes belong to Deuteromycetes class. Dermatophytes: a group of organisms that can break down 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. The most important dermatophytes that cause infection in humans are classified into: 1- Trichophyton: infection on skin, hair, and nail. 2- Microsporum: Infection on skin and hair 3- Epidermophyton: Infection on skin and nail The dermatophytes based on their natural habitat and host preferences can be classified into: Anthropophilic: Associated with human Only person-to-person transmission through contaminated objects (Fallen hair, combs, hat, ….) 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 dead organic substances They occasionally cause infection in humans and animals Examples: Microsporum gypseum and Trichophyton ajelloi Clinical features Dermatophytes usually grow only on keratinized skin and its appendages and do not penetrate the living tissue. The skin infections caused by dermatophytes are chronic infections of the skin often found in the warm humid area of the body. Symptoms and signs vary by site of infection. Typical ringworm lesions are circular, dry, erythematous, scaly, and itchy which have inflamed borders containing papules and vesicles surrounding a clear area or relatively normal skin These lesions are associated with variable degrees of scaling and inflammation Nails are thickened, deformed, friable, discolored, and subungual debris accumulation. Dermatophytid reaction(Id) In some infected persons, hypersensitivity to fungus antigens may cause secondary eruptions such as vesicles on the finger This reaction is known as the dermatophytid (Identity ) reaction (Id) This reaction occurs as a result of a hypersensitivity response to circulating fungal antigens, and these lesions do not contain any fungal hyphae Dermatophytosis clinical classification Infection is named according to the anatomic location involved: A. Tinea barbae B. Tinea corporis C. Tinea capitis D. Tinea cruris (jock itch ) E. Tinea pedis (Athlete’s foot) F. Tinea manuum G. Tinea unguium Tinea capitis Also known as ringworm or herpes tonsurans infection. This infection of scalp hairs is caused by Microsporum and Trichophyton. It penetrates the hair cuticle and typically invades the hair shaft in one of three ways: Ectothrix infection: the dermatophyte grows within the hair follicle and covers the surface of the hair. Fungal spores are evident on the outside of the hair shaft and the cuticle is destroyed. M. canis is an ectothrix dermatophyte. Endothrix infection: the dermatophyte invades the hair shaft and grows within it. Fungal spores are retained inside the hair shaft, and the cuticle is not destroyed. T. tonsurans is an endothrix dermatophyte. Favus infection: a chronic dermatophyte infection caused by T. schoenleinii and characterized by clusters of hyphae at the base of the hairs, with air spaces in the hair shafts. Clinically there is yellow crusting around the hair shaft Tinea corporis This is a disease of the glabrous (Non-hairy) skin of the body and may result from the extension of infection from the scalp, groin, or beard. Characterized by erythematous scaly lesion, annular, sharply marginated plaques with raised borders which may be single, multiple, or confluent Tinea pedis This is the infection of the plantar aspect of the foot, toes, and interdigital web spaces It is frequently seen among individuals wearing shoes for long hours and is popularly known as Athlete’s 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 the infection becomes chronic, the sole becomes hyperkeratotic and is often covered with fine scales Tinea pedis Tinea Barbae Infection of beard and mustache area of the face with the invasion of coarse hairs Also called a barber’s itch There are erythematous patches on the face which show scaling Tinea Cruris Dermatophytics infection of the groin Involves perineum, scrotum, and perianal area and may spread to the inner third of buttock and occasionally to high The appearance of Tinea Cruris can be seen in other intertriginous areas such as the axilla and around the umbilicus of obese patients Tinea Cruris Tinea Manuum Dermatophyte infection of the skin of palmar of hands The most common clinical manifestation is diffuse hyperkeratosis of palms and fingers Tinea Unguim Dermatophyte infection of nail plates is largely a disease of adults. It begins under the leading free edge of the nail plate or along the lateral nail fold and may continue until the entire nail plate and nail bed are infected There is an accumulation of subungual debris is an opaque, chalky, or yellowish thickened nail Laboratory diagnosis Specimens Scrapings of skin and nail Short hair plucked from the scalp Scraping is taken from the edges of ringworm lesion Direct microscopic examination KOH wet mount 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) Wood’s lamp Culture Species identification is possible only by cultural examination Subouraud dextrose cycloheximide agar containing chloramphenicol and The plate was incubated aerobically at 25-30o c for up to 21 days Identification in the laboratory by 1. Macroscopic examination (characteristic of the fungal colonies) 2. Microscopic examination Trichophyton Microsporum canis Epidermophyton floccosum Treatment This is by using topical preparation (ointment or gels containing azoles( miconazole, clotrimazole, econazole) or terbinafine Oral preparation of griseofulvin, azole( Ketoconazole, itraconazole) or terbinafine Treatment