cause disease by parasitism, invasion (dissemination), allergic diseases, toxicoxes (ie mushrooms)
eukaryotic; no chloroplasts
Þ not plants
cell wall of chitin - very strong substance; also in insect exoskeletons and lobster/crab shells; possible anti-fungal target
ergosterol
in cell membrane (instead of cholesterol); main target of anti-fungals
yeasts
: round; reproduction via budding; slimy appearance
molds
: hyphae (long, threadlike filaments); fluffy or granular appearance
Dermatophytes
cutaneous mycoses (invade stratum corneum, nails, hair); also known as ringworm
anthrophilic
(human-human transfer - most common; no inflammation); geophilic (soil-human - mild inflammation); zoophilic (animal-human - extensive inflammation)
features of tineas: scaly, annular (ring-shaped); erythematous patches; pruritic; no response to topical steroids
Microsporum canis
: zoophilic spread; mostly via cats/dogs
Trichophyton tonsurans
: anthrophilic spread; most common cause of tinea capitis in US
Trichophyton rubrum
: most common infection
tinea capitis
: T. tonsurans most common; also M. canis outside US (cat/dog vector); tinea barbae infects male beard
more common in children and Af. American, Hispanic populations
hair loss (alopecia) and cervical lymph node enlargement are common presentations
Kerion (a type of inflammation): edematous, crusting, scaly, well-circumscribed (resembles bacterial furunculosis)
Black dot type (endothrix invasion): hair breaks off at scalp, leaves black dots
treatment: griseofulvin ~8 wks until hair grows back
tinea pedis
(athlete’s foot): T. rubrum (most common), T. tonsurans; tinea manuum is similar but pertains to hands
presents as moccasin, inflammatory, interdigital, or ulcerative types; scaly, red, dry; infection rare before puberty
tinea cruris
(jock itch): T. rubrum (most common), T. tonsurans
scaly rash in bilateral proximal medial thighs and groin; scrotum, penis, vulva rarely involved
more common in males
candida infection is similar; candida may have satellite pustules and may affect scrotum
tinea corporis
(ringworm): T. rubrum most common; also M. canis (more inflammatory); tinea facei - ringworm on face
annular, scaly, pruritic, red patch with distinctive border; infects trunk, back, and extremities
usually treatable with topical drugs (non-responsive to topical steroids)
tinea unguium
: (infection of nail): T. rubrum (most common), T. tonsurans
onchomycosis: general term for fungal infection of finger and toe nails
most often begins with distal nail and progresses proximally; nail becomes thick and scaly
proximal white onchomycoses
begins at cuticle (sign of possible HIV infection)
Superficial Mycoses
– invades only the outer layers of the hair, skin, nails
tinea (pityriasis) versicolor
: yeast, not dermatophyte, so not true tinea
slightly scaling macules; hypo or hyper pigmented spots; generally affects trunk, neck, upper arms
more common in hot humid climates or season; most common in mature ages localizing near sebaceous glands
hypo pigmented spots will not tan due to ‘sunscreen’ produced by the organism
round budding cells and hyphae give ‘spaghetti and meatballs’ appearance under microscope
treatable with topical or oral drugs (azole class); however, high rate of recurrence
tinea (pityriasis) nigra
: not dermatophyte, so not true tinea
asymptomatic, nummular, macular brown/black patches on palms or soles; often mistaken for melanoma
infection most often from soil in southwest/coastal states; most common in teens and females more than males
topical treatment with an antifungal agent in the imidazole class is generally effective
piedra
: superficial mycosis of hair shaft; Treatment: cutting or shaving hairs
comes in white (genital/facial area) and black (scalp/facial area) piedra (from unrelated organisms)
candida
: yeast - affects mouth, skin folds, vagina
Candida albicans: most often affects mouth - thrush; may present whitish and slimy
cutaneous candidiasis: most often affects skin folds; moist red lesions; may have satellite pustules
risk – DM, obesity, pregnant, systemic antibiotics/steroids; may become invasive in immunocompromised patient
Diagnosis
KOH exam
: scrape edge of lesion Þ add 1-2 drops of KOH to scrapings on a glass slide to dissolve eukaryotic material Þ pass once through flame to accelerate process Þ observe via microscope under low power
Wood’s light exam: UV light; some species of Microsporum fluoresce yellow-greenish; diagnositc for tinea capitis
culture can distinguish dermatophytes via colony morpholgy; biopsy rarely necessary
Treatment
– anti-fungals
Griseofulvin
: nuclear target; kills dermatophytes; not yeast
oral drug used when topicals are ineffective (main indications: capitis; immunocompromised patient; anychomycoses)
Azoles
(ketoconazole; fluconazole; itracanazole): targets ergosterol synthesis; kills dermatophytes and yeast
oral or topical; ketoconazole comes in both flavors
Terbinafine
(allylamine family): targets ergosterol systhesis in cell membrane; kills dermatophytes; not yeast