Fungal Disease Lecture Notes PDF

Organization of Fungal Disease Lec.3 Mycoses fall into three categories 1- Cutaneous mycoses: Microsporum, Trichophyton and Epidermophyton 2- Subcutaneous mycoses: Sporothrix schenkii 3- Systemic mycosis: Cryptococcus neoformans Coccidioides immitis Histoplasma capsulatum Candida spp. Aspergillus sp...

Organization of Fungal Disease Lec.3 Mycoses fall into three categories 1- Cutaneous mycoses: Microsporum, Trichophyton and Epidermophyton 2- Subcutaneous mycoses: Sporothrix schenkii 3- Systemic mycosis: Cryptococcus neoformans Coccidioides immitis Histoplasma capsulatum Candida spp. Aspergillus spp. Cutaneous Fungal Infections Dermatophytoses Dermatophytosis - "ringworm" disease of the nails, hair, and/or stratum corneum of the skin caused by fungi called dermatophytes. Dermatomycosis - more general name for any skin disease caused by a fungus. Dermatophytoses Infections were previously called ringworms because they resemble a worm lying below the surface of the skin, and by the Romans ‘tinea' (which means small insect larvae) dermatophytes :molds producing keratinase use keratin as a nutrient source and thus colonize only dead layers of skin, nails, and hair No living tissues are infected Dermatophytoses are among the most prevalent fungal infections in the world ▪Dermatophytoses :The infections are caused by a group of fungi called Dermatophytes (a group of about 40 related fungi that belong to three genera: Microsporum - infections on skin and hair (not the cause of TINEA UNGUIUM) Epidermophyton - infections on skin and nails (not the cause of TINEA CAPITIS) Trichophyton - infections on skin, hair, and nails. Dermatophtyes are classified into three groups Anthropophilic(keratin-utilizing on hosts – humans) Fungi of humans that are transmitted by human contact or infected objects Zoophilic(keratin-utilizing on hosts – living animals) Fungi of animals that are transmitted by contact with animals or their products Geophilic (keratin-utilizing soil saprophytes)soil fungi that are transmitted to humans via exposure to soil or dusty animals Some anthropophilic species are geographically restricted, but others are globally distributed, such as: Epidermophyton floccosum Trichophyton mentagrophytes Trichophyton rubrum Trichophyton tonsurans The most common geophilic species causing human infections is Microsporum gypseum. The most common zoophilic species are: - Microsporum canis (dogs and cats) - Microsporum gallinae (fowl) -Microsporum nanum (pig) - Trichophyton equinum (horses) - Trichophyton verrucosum (cattle) Major sources of ringworm infection Schools, military camps, prisons. Warm damp areas (e.g., tropics, moisture accumulation in clothing and shoes). Animals (e.g., dogs, cats, cattle, poultry, etc.). Microsporum species ▪ Microsporum spp. infect only hair and skin, but not nail ▪ They form many multicellular macroconidia with rough walls, and few microconidia ▪ M. canis forms a colony with a white cottony surface, macrocoinidia usually is curved or hooked tips, contains 8-15 celled macroconidia ▪ M. gypseum produces a tan, powdery colony and abundant thin-walled, 4-6 celled macroconidia Microsporum M. canis M. nanum M. audouinii M. gypseum M. cookei Trichophyton species ▪ They form few macroconidia and many microconidia, they infect the skin, hair and nail, they infect endothrix and ectothrix ▪ The typical colony of T. rubrum has a white, cottony surface and a deep red, non-diffusible pigment when viewed from the reverse side of the colony ▪ T. tonsurans produces a flat, powdery colony and a reddish-brown colony when observed from the reverse side. T. mentagrophytes T. rubrum T. rubrum T. verrucosum T. tonsurans Epidermophyton species ▪ Epidermophyton floccosum, which is the only pathogen in this genus, produces only macroconidia, which are smooth-walled, 2-4 celled, and formed in groups of two or three ▪Shape of macroconidia is a distinguishing characteristic - clavate macroconidia. ▪ The colonies are flat and give a tan to olive-green color ▪E. floccosum infects the skin and the nails but not the hair. E. floccosum Epidermophyton E. floccosum Clinical manifestations of ringworm infections are called different names on basis of location of infection sites A single species is able to cause more than one type of clinical infection tinea capitis - ringworm infection of the head, scalp, eyebrows, eyelashes tinea corporis - ringworm infection of the body (smooth skin) tinea cruris - ringworm infection of the groin (jock itch) tinea unguium - ringworm infection of the nails tinea barbae - ringworm infection of the beard tinea manuum - ringworm infection of the hand tinea pedis - ringworm infection of the foot (athlete's foot) Tinea pedis (athlete’s foot) ▪ It is the most prevalent of all dermatophytoses It usually occurs as a chronic infection between toes or toe webs - 4th and 5th toes are most common. Soreness and itching of any part of the foot and somtimes affect the sole leading to hyperkeratosis of the sole ▪ The infected area will be covered by white macerated tissues (releasing of clear fluid) accompanied by pain and pruritus, and the infected area is prone to secondary bacterial infection ▪ The main causative dermatophytes are: T. rubrum T. mentagrophyte E. floccosum Tinea pedis Tinea unguium (onychomycosis) ▪ It is a nail infection that may follow prolonged tinea pedis, with hyphal invasion the nails become yellow, brittle , thickened, and crumbly ▪ The main causative agents are: T. rubrum T. mentagrophyte E. floccosum Tinea unguium Tinea capitis ▪ Tinea capitis (black dot) is a widespread scalp infection in children caused by dermatophytes ▪ Some factors implicated in infection include poor personal hygiene, crowded living conditions, and low socioeconomic status ▪ It can be caused by any pathogenic dermatophyte except for Epidermophyton floccosum ▪In developing countries, the most common agent is Microsporum canis followed by Trichophyton tonsurans ▪ The infection produces dull gray, circular patches of alopecia, scaling, and itching. Tinea capitis Tinea barbae (barba’s itch) ▪ It involves the bearded region ▪ When a zoophilic dermatophyte is involved a highly inflammatory reaction may be seen resembling a pyogenic infection Tinea corporis ▪Produces concentric or ring-like lesions on skin, and in severe cases these are raised and may become inflamed. ▪ The dermatophye grows only within dead, keratinized tissue, but fungal metabolites, enzymes, and antigens diffuse through the viable layers of the epidermis to cause erythema, vesicle formation and pruritus ▪ The infection usually affects trunk, limbs and sometimes face ▪ The main causative agents are: M. canis T. mentagrophyte T. rubrum Tinea cruris (jock itch): When the infection occurs in the groin area, it is called Tinea cruris, or jock itch. Most of these infections involve males and present as dry, itchy lesions that often start on the scrotum and spread to the groin. Tinea Manus: It is ringworm of hands or fingers. Dry scaly lesions may involve one or both hands, single finger or more fingers. Tinea cruris Tinea manus Trichophytid reaction ▪ In the course of dermatophytosis, the patient may become hypersensitive to constituents or products of the fungus and develop allergic manifectations called dermatophytids (usually vesicles) anywhere on the body, most often on hand ▪ The trichophytin skin test is positive (crude antigen preparation that can be used to detect immediate or delayed type hypersensitivity to dermatophytic antigens) Dermatophytid Reaction Diagnostic laboratory tests - Specimens: Scrapings from both skin and the nails plus hairs plucked from involved areas Microsporum-infected hairs fluoresce under Wood’s light in a darkened room - Microscopic examination: Specimens are placed on a slide in a drop of 10-20% KOH : Branching hyphae or chains of spores are seen. In case of microsporum species a dense sheaths of spores around the hair (ectothrix) are seen. Ectothrix and Endothrix Arthroconidia on hair Fluorescing hair (under Wood's lamp) is seen in dogs and cats infected with some dermatophytes - Culture: Sabouraud’s agar specimen incubated on this medium for 1-3 weeks at room temperature. Species are identified on the basis of colonial morphology (growth rate, surface texture, and pigmentation). Microscopic morphology (macroconidia, microconidia). Treatment ▪ Therapy consists of good removal of infected and dead epithelial structures and application of a topical antifungal agent or antibiotics. ▪ To prevent reinfection, the area should be kept dry, and sources of infection such as an infected pet or shared bathing facilities should be avoided. Antifungal agents: Griseofulvin Miconazole Ketoconazole Terbinafine