Superficial fungal infections Flashcards
What are Dermatophytes?
Moulds. Superficial and cutaneous infections. Like keratin (skin, nails, hair).
Genera of dermatophytes
Trichophyton, microsporum, epidermophyton
Other agents that could be part of superficial infection DDX
Staphylococcus aureus, Streptococcus pyogenes; Endemic fungi like Histoplasma, Blastomyces, and Coccidioides; Parasitic or viral rash; Allergy and other non-infectious etiologies
Tinea - what’s it mean?
Latin for worm, refers to the lesions (no worms involved). Tania is genus for tapeworm
Tinea classification
Tinea capitis - head. Tinea corporis – trunk. Tinea cruris - groin. Tinea pedis - feet. Tinea unguium – nails. This is not genus-species setup
Sources of dermatophytes
Human, animal, soil
Pathogenesis of dermatophytes
Enter via skin breaks (groin and toes prone due to use, moisture). Bind keratinocytes and invade with keratinases, germinate and infect. Usually restricted by temp (prefer 30C).
Pathogenesis of dermatophyte in skin infection
Spread through stratum corneum. Growth outward in centrifugal pattern (ring). Viable fungi are at margin or leading edge. No viable organisms in centre of lesions
Pathogenesis of dermatophyte in nail infection
Invasion of lateral or superficial nail plates. Spreads throughout nail
Pathogenesis of dermatophyte in hair
Ectothrix (infects outside of hair shaft) and Endothrix (infects inside of hair shaft)
Acute and chronic dermatophyte infection
Acute has inflammatory lesions due to immune system, sometimes pustules (often from non human), Chronic is less severe and is usually human-human
Tinea capitis
Scalp ringworm, Hair shafts infected. M. canis, M. audouinii. Often from dogs and cats. Children predisposed (Poor hygiene, prolonged moist skin). Scaling of scalp, hair loss, itching. Quite transmissible. Resembles dandruff
Tinea corporis
Aka Ringworm on body; trunk and legs. Trichophyton spp. Most lesions have prominent edge + pustules. Centre of lesion less inflammed and scaly. Uncommon in temperate climates.
Tinea pedis
aka Athlete’s foot. Interdigital spaces between toes, soles. Itching, erythema, scaling. Causes: E. floccosum, T. mentagrophytes. Poor hygiene, sports, wet occupation, Gym class and teenagers
Tinea cruris
aka Jock itch. Causes: T. rubrum, E. floccosum. Scaling and irritation of groin, rash migrates to inner thigh, pustules uncommon. Disease of young men. Anthropophilic (ie human-human) (military and institutionalized)
Tinea unguium
Nail infections, Aka – onychomycosis. Causes: T. rubrum, Candida spp (a yeast!). Nail invasion leads to thickening and discolouration (White, yellow, or brown)
Micro diagnosis of dermaophyte disease
Skin/nail scraping, hair stubs. Look under direct microscopy, fungal culture
Tinea versicolour
Superficial infection caused by yeast. Not related to poor hygeine, mostly cosmetic. Malassezia sp. (Lipophilic yeast that colonizes normal skin, Most adults colonized, Not a dermatophyte). Lesions on Trunk and limbs, Hypo- or hyperpigmented skin patches. Versicolor – variable changes in skin pigmentation. May be macular. Scaling is mild. Not in nail bed or hair
Opportunistic infections of Malassezia
Catheter-related fungemia, Neonates, Inntavenous lipids for parenteral nutrition (High triglyceride content). More serious, not just limited to superficial
Sporotrichosis
Thermally dimorphic fungus. Yeast at 37ºC and mould at 25ºC!! Not restricted geographically like ‘Endemics’. Subcutaneous infection, Deep, ulcerated skin lesions; can track up lymphatic tract; Rarely invade deeper tissues.
DDX of tracking skin lesions
Nocardia (bac in dirt), Atypical mycobacteria (M. marinum - often in fish tanks), Leishmania species (in middle east)
Pathogenesis of sporothrix
Thorn, barb, pine needle injury introduces Conidia (from mould phase). Localized infection (several days). Fungal spread along lymphatic channels (Chain of nodular lesions). Lesions are suppurating granulomas: Hystiocytes and giant cells (Surrounded by neutrophils, lymphocytes, and plasma cells)
