5 Dermatomycoses Flashcards
Which species are considered cutaneous fungi?
Malassezia furfur
Hortaea werneckii
How are dermatophytes different from cutaneous fungi?
Pathogenic fungi
Require keratin for growth (hair, nails, skin)
Do not infect mucosal surfaces
Secrete keratinase (allows for inhabiting keratinized regions of the body)
Important genera of dermatophytes
Epidermophyton
Microsporum
Trichophyton
What makes dermatophytes morphologically identifiable?
Hyphae and arthoconidia can be visualized in dead keratinized tissue
How do you culture dermatophytes for diagnosis?
If onychomycosis, culture material under nails
Sabouraud agar at room temp for 1-3 weeks
DERMATOPHYTES TEST MEDIUM (DTM) allows for early detection
How does Dermatophytes test medium work?
Selective (cyclohexamide and abx) and differential (color change based on fermentation of sugars)
Dermatophytes utilize nitrogenous compounds preferentially over carbs
Change in pH (alkaline) —> red color change
What is the infective stage of dermatophyte?
Arthroconidium - can be visualized microscopically in 10% KOH wet mount
How is the morphology of Trichophytin different?
Galactomannan peptide
Crude antigen of dermatophytes
• CHO component-intermediate response
• Peptide component-delayed response
How does 10% KOH work?
Digests human tissue, leaves fungal components intact
What classification of dermatophyte:
Animal pathogens that may be transmitted to people
Zoophilic
What classification of dermatophyte:
Human transmission
Antrophophilic
What classification of dermatophyte:
Transmitted through soil to people
Geophilic
Usually invade non-viable keratinized tissue
What are the favored habitats for dermatophytes?
Moist areas of the body
What parts of the world will you find dermatophyte infections?
Worldwide, but most prevalent in the tropics
What are arthrospores?
Fragment hyphal elements in hair, nails, outer skin
Also see infections by microconidia, macroconidia, and sexual spores
How do dermatophyte infections typically present in people?
Lesions are inflamed at edges, with a central clearing zone
Hair loss with itching, but not debilitating
Predisposing factors for dermatophytosis?
Nail trauma, HIV, DM, immunosuppressive meds
Risk factors for dermatophytosis
Communal bathing facilities, immunocompromised status, Cushing syndrome (increased cortisol interferes with inflammation) and some contact sports (ie wrestling)
Disseminated disease from dermatophytes is possible in …
HIV patients
Typically T. mentagrophytes and M. canis
What are the different fungal elements you might see on KOH?
Arthrospores (arthroconidia) - the infectious element, survives in environment
Microconidia
Macroconidia (usually multicellular)
What is Dermatophytid?
“Id reaction”
Allergic dermal reaction to fungal antigens occurring in areas devoid of organisms
Most common in Tinea pedis
Sometimes a result of excessive treatments or pruritis
How is dermatophytid treated?
As an allergy
Corticosteroids (systemic or topical)
Wet compresses
Antihistamines (systemic or topical)
How do you treat dermatophyte infections?
Antifungal agents
• Azole creams (miconazole, clotrimazole)
• Systemic antifungals (terbinafine, itraconazole)
Laser and removal of the infected tissue (ie nail)
How do azoles and terbinafine work in treating fungal infections?
Interfere with sterol synthesis in the cytoplasmic membrane of the fungus
Control measures to prevent dermatophyte infection
Good personal hygiene
Keep skin as dry as possible
Spores are shed on skin and hair (regular housecleaning important)
Spores are generally susceptible to common disinfectants, chlorine bleach, and detergents
What are the clinically relevant species of Trichophytons?
T. tonsurans
T. rubrum
T. mentagrophytes**
How are trichophytons distinguishable from other dermatophytes?
Not often fluorescent
All make pencil-shaped macroconidia with thin walls
Produce hyphae (spindle shaped), microconidia, macroconidia
Most common of cause of tinea capitis
Microsporum canis
Can also be due to T. mentagrophytes or T. tonsurans
What makes microsporum species identifiable?
Fluorescence when examined with a wood’s lamp
Produce hyphae, microconidia, macroconidia (large, spindle shaped; multicellular; thick walled)
Name the area affected:
Tinea barbae
Beard
Name the area affected:
Tinea capitis
Scalp
Name the area affected:
Tinea corporis
Arm, leg, torso
Name the area affected:
Tinea cruris
Groin
Name the area affected:
Tinea manus
Hand
Name the area affected:
Tinea pedis
Foot
Name the area affected:
Tinea unguium
Nails
Tinea capitis is mostly a ________ disease
Childhood
Involves the hair and scalp
Endothrix ringworm infections are usually from…
Trichophyton
Ectothrix ringworm infections are usually from…
Microsporum
Black dot ringworm gets its appearance from…
Broken hair follicles
Infected hair can break off leading to alopecia
Intense inflammation, scarring and permanent alopecia can occur
Tinea capitis can be acquired from…
Kittens and puppies (zoonotic)
What is a good systemic treatment for tinea capitis?
Griseofulvin
Agents that cause tinea pedis?
E. floccosum, T. mentagrophytes, T. rubrum
Tinea pedis is characterized by …
Itching, peeling, and cracking of the skin, usually toe webs and soles
Most prevalent of all dermatophytoses
Tinea pedis
Predisposing factors for tinea corporis and tinea cruris?
Diabetes, obesity, excessive perspiration
Transmission can be either direct or indirect (contaminated objects like towels, clothing, bed linens)
What gender is more commonly affected by tinea corporis/cruris?
Men
Tinea unguium is another name for …
Onychomycosis (ringworm of the nail)
Finger and toenails become discolored and thick
May be mistaken for psoriasis
Tinea unguium is commonly caused by…
E. floccosum, T. mentgrophytes, T. rubrum
Tinea unguium usually has ______ involvement as well
Fungal (candida)
Preferred treatment for tinea unguium
Systemic antifungals better than topical agents
Most commonly encountered opportunistic mycoses worldwide
Candidiasis
Normal flora of the skin, mucous membranes that colonize mucosal surfaces soon after birth
Underlying causes of candidiasis
Absence of competing normal flora
Introduction to abnormal site
Pathologic change in microenvironment
Inborn or acquired immune defect
Use of broad-spectrum abx
What factor helps Candida albicans adhere the most?
Germ tube more adhesive than yeast cell
Not many virulence factors other than that
How is candida diagnosed?
Direct microscopic exam —> gram stained samples show large G(+) cells
Will also see yeast cells, pseudohyphae, and true hyphae
What kind of culture can you do for candida?
Chromagar (will show hyphae and pseudohyphae in addition to germ tubes)
Why is serology difficult for candida?
It’s normal flora
Many have had prior exposure
Low tigers of antibody
How do you treat candida?
Topical cream (miconazole) or oral fluconazole
Tinea versicolor is caused by…
Malassezia furfur (cutaneous fungi)
What does Malassezia furfur look like?
Microscopically: short, unbranched hyphae and somewhat spherical cells (SPAGHETTI AND MEATBALLS)***
Malassezia furfur has what growth factor?
Lipophilic
Requires fat to grow —> likes sebaceous glands
Who is more commonly affected by tinea versicolor?
Young adults
Occurs worldwide but more common in the tropics
What does a tinea versicolor infection look like?
Lesions occur as a macular patch of depigmented or hyperpigmented skin that may enlarge
Can lead to dandruff as well
Diagnosis of tinea versicolor is via…
Microscopic exam of skin scrapings in KOH
Treatment for tinea versicolor
Topical selenium sulfide, miconazole
Tinea nigra is a cutaneous fungi caused by …
Hortaea werneckii
What distinguishes Hortaea werneckii from other species?
Dimorphic species (can grow as yeast and/or mold)
Can grow in saturated salt solutions (extreme halotolerance)
How does tinea nigra present?
Brownish lesion (fungus produces melanin)
How do you diagnosis tinea nigra?
KOH and microscopy
Treatment for tinea nigra?
Tincture of iodine or azole creams
