Fungal Infections of the Skin Flashcards
Dermatophytosis organisms
causes by dermatophytes. infect superficial keratinized structures (skin, hair, nails). three major genera, epidermophyton, trichophyton, microsporum. all transmit by direct contact except microsporum, which is by zoonosis from pets. all produce keratinases that allow invasion of the cornified cell layer
dermatophytosis pathogenesis
form chronic infections in warm, humid areas on body surface. named for affected body part. form inflamed circular border of papules/vesicles. transmitted by fomites or by autoinoculation from other body sites
dermatophytosis diagnosis
exam: itching, redness, tight/wet clothing. Scraping from skin/nail, treat with KOH, examine remains for spores/hyphae. culture on sabourauds agar, PPD with trichophytin, microsporum show fluorsecence under wood’s lamp
dermatophytosis treatment
topical antifungal cream: terbinafine, undecylenic acid, miconazole, tolnaftate. can use oral griseofulvin
tinea versicolor organisms and pathogenesis
overgrowth of normal flora Malassezia furfur or globosa. superficial skin infection only cosmetic. hypo/hyper pigmented areas with scaling/itching. family often has a history of infection
tinea versicolor diagnosis
skin scrapings, treat with KOH and stain with blue. look for mix of budding yeasts and short cigar butt hyphae. examination with wood’s lamp might show coppery-orange fluorescence
tinea versicolor treatment
topical selenium sulfide or azole for 2 weeks. can use oral azoles too
tinea nigra organisms and pathogenesis
organism is the werneckiis. spores in soil enter injury, germinate in the keratinized skin layers. generate a brown pigment. seen in southern coastal US.
tinea nigra diagnosis
brown spots, slight itch. treat skin scrapings with KOH, examine for thick septate, branching hyphae with dark pigment in their walls. culture on sabouraud’s agar. shiny black colonies in 1 week
tinea nigra treatment
topical keratolytic agen to break down infected skin and a topical azole
sporotrichosis organism
sporothrix schenckii. thermally dimorphic!! found on vegetation, often seen in gardeners of roses
sporotrichosis pathogenesis
thorn puncture. yeasts grow at site and form painless pustule or ulcer. suppurating subcutaneous nodules. symptoms wax and wane over the years. may progress to disseminated disease and meningitis if immunosuppressed. patients with COPD and long term corticosteroid use may develop pulmonary probs from inhaling spores
sporotrichosis diagnosis
painless pustule or ulcer. history of gardening, farming, etc. history of ineffective antibiotic treatment. AIDS patients may have nodules on whole body. tissue biopsy shows round or cigar shaped budding yeasts. culture shows hyphae with oval conidia in clusters at tip of slender conidiophores (daisy shaped)
sporotrichosis treatment and prevention
treat with itraconazole or other azoles. for more serious types, amphotericin B. wear gardening gloves to prevent
chromomycosis organism
chromoblastomycosis or dermititis verrucosa. caused by dermatiaceous fungi: fonsecaea, phialophora, cladosporium. found in soil in the tropics, conidia or hyphae are gray or black
chromomycosis pathogenesis
introduced into legs or feet with injury by wood splinters or thorns. gradually progressive subcutaneous disease. granulomas form as immune system attempts to contain. wartlike lesions spread from initial site over the years
chromomycosis diagnosis
history of farming or travel. wartlike dark lesions. crusting abscesses along lymphatics. black dots among lesions. KOH mount from skin scrapings show dark colored septate hyphae or conidia. biopsy shows round fungal cells inside leukocytes or giant cells. ELISA for some species
chromomycosis treatment and prevention
oral flucytosine and itraconazole. combine with local surgery. cryosurgery can be effective. topical application of heat from pocket warmers also helps reduce and reverse fungal growth over the months. wear shoes!!!
mycetoma organism
petriellidium or madurella. found in soil, enters in wounds. rare in the USA
mycetoma pathogenesis
replicating fungi form abscesses. pus containing compact colored granules forms and drains through the local sinuses. looks very similar to actinomycosis, forms in foor, lower leg, or hand rather than the face though. granulomatous inflammatory response in the deep dermis and subcutaneous tissue may extend to bone. after years of infection, initial painless nodule swells and bursts!!!!
mycetoma diagnosis
needle biopsy and culture. grains in the pus. Xray to see if bone is involved. differentiate from actinomycosis by staining. tissue gram stain to see fine gram positive branching filaments of actinomycetoma grain. silver or acid schiff stain to see larger hyphae of eumycetoma.
mycetoma treatment
first attempt antifungal therapy: admit for initial IV amphotericin B, add antibiotics for secondary infections and send home with oral azole. surgical excision of abscesses necessary usually
candidiasis organisms
candida albicans. large, yeastlike, oval with a single bud. may also appear as pseudohyphae or hyphae when invading tissues
candidiasis pathogenesis
adhesins for attachment, acid proteases and phospholipases for tissue invasion, phenotypic switching changes antigen expression and tissue affinity. syndromes range from trivial superficial to life threatening systemic. may involve any anatomical structure. difficult to diagnose as a pathogen since they re normal flora
