Fungal Skin Diseases Flashcards
1
Q
What causes Dermatophytosis? (ringworm)
A
- Common Isolates:
- Microsporum canis
- Microsporum gypseum
- Trichophyton mentagrophytes
- Dermatophytes grow in the keratinized tissue of skin, hair or nails
- invade hair follicles and hair shafts. Enzymes enable the fungus to penetrate the hair and grow within the shaft
- Infect hair that is in the anagen stage
- Fungus advances toward the hair bulb and toxins produced in the stratum corneum incite cutaneous inflammation
- if the infected hair stops growing, fungal growth stops
- invade hair follicles and hair shafts. Enzymes enable the fungus to penetrate the hair and grow within the shaft
- Incubation 1-3 weeks
2
Q
What are the clinical signs of dermatophytosis?
A
- Lesions - circular patches of alopecia w/ scale (variable)
- On head, pinnae and extremitis
- Broken hairs
- Folliculitis, furunculosis (papules, crusts)
- Kerion - exudative fungal nodule uncommon in dogs
- Pruritus - absent or mild
- Cats may have minimal inflammatory response
- Onychomycosis - Rare
- Dermatophytic pseudomycetomas
- cutaneous to subcutaneous nodules of fungal aggregates, amorphous material and granulomatous inflammation
- uncommon - Persian cats
- cutaneous to subcutaneous nodules of fungal aggregates, amorphous material and granulomatous inflammation
3
Q
How is Dermatophytosis Diagnosed?
A
- Wood’s light
- bright, apple-green fluorescence of hair shafts
- scale and debris on skin is usually yellow/gold
- Microscopic examination of hair
- visualize fungal hyphae (clear, wavy lines in hair shaft)
- Arthrospores (fragmented pieces of hyphae that appear as tiny, clear “dots” on hair shafts)
- 10%KOH may enhance visibility of fungal elements
- Fungal culture
- Most reliable
- Sample broken hairs - hairs that appear to fluoresce
- pluck with hemostate or collect w/ toothbrush
- Media :
- Sabouraud’s dextrose agar
- Dermatophyte test medium (DTM)
- like Sabourauds +antimicrobials and pH indicator (phenol red)
- Others
- Biopsy
- usually not as sensitive as culture
- more useful with nodular manifestations
- PCR
- can be positive w/out active infection
- Rule out other causes
4
Q
What is the DTM technique for testing for Dermatophytosis
A
- Embed sample into media
- Cap loosely and store in the dark, room temp, 30% humidity
- Check daily for growth and media color change
- Pathogenic fungi first use protein in the media and produce alkaline metabolites that turn media red
- Non-pathogenic fungi usually use carbohydrates first and proteins later
- media turns red but 1-2 weeks after apparent growth
- Red color w/ simultaneous colony growth = Positive
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5
Q
What is the treatment for Dermatophytosis? (Broad terms)
A
- Systemic (not always necessary)
- Topical (Always)
- Continued until 2-3 negative cultures (weekly)
- or continue treatment for 2-4wks after resolution of clinical signs if not culturing
- Environmental decontamination
6
Q
What are the systemic treatment options for Dermatophytosis
A
- Itraconazole
- teratogenic
- 5-10mg PO q24h
- Terbinafine
- Potentially teratogenic
- 30-40 mg/kg PO q24h
- Ketoconazole
- inhibits P-450 enzymes & P-glycoprotein
- may be ineffective for M. canis
- Cats - hepatotoxicity and GI signs
- Teratogenic
- 5-10 mg/kg PO q12-24h
- Fluconazole - poor efficacy
- Griseofulvin - NO - bone marrow sppression
- Lufenuron - not actually effective
7
Q
What topical treatments are done for Dermatophytosis
A
- Total body clip
- Lime sulfur dips
- Miconazole/Ketoconazole w/chlorhexidine rinses/shampoos
- Whole body treatment 1-2x weekly
- Antifungal creams, lotions, rinses may be used for spot treatment of isolated, focal lesions
8
Q
What causes Malasseziasis?
A
-
Malassezia pachydermatis (and other species of yeasts)
- Normal flora of skin and ear canal
- Commensal of anals sacs and mucosal srfaces
- Yeast become pathogenic under certain circumstances
- lowered host defense, change in microclimate, allergic dermatitis, seborrhea, pyoderma, etc
9
Q
What are the clinical signs of Malasseziasis
A
- Erythema, scaling, alopecia, lichenification, hyperpigmentation, odor (musty)
- red-brown discoloration of nails if affected
- Greasy/tacky feeling skin
- Yeast Dermatitis - ventral neck, axillae, ventral abdomen, feet & nails, skin folds
- Yeast otitis - ear canals
- Usually very pruritic
10
Q
How is Malasseziasis diagnosed
A
- Cytology - best
- Biopsy may not show yeast
- Culture
- Response to antifungal treatment
11
Q
What is the treatment for Malasseziasis dermatitis?
A
- Topical therapy - may be effective alone
- Miconazole
- Ketoconazole
- clotrimazole
- chlorhexidine (≥3%)
- acetic acid-based products
- Systemic Antifungals
- Ketoconazole
- itraconazole
- fluconazole
- terbinafine
- Pulse dosing of Systemic antifungals and maintenance topical therapy may be necessary to prevent recurrent dermatitis
12
Q
What is the treatment for Malasseziasis otitis?
A
- Clean ear canal
- Topical anti-yeast otic preparations
- Systemic antifungals - rarely needed
13
Q
What are the Subcutaneous Mycoses?
A
- Pythiosis
- Sporotrichosis
14
Q
What are the Systemic Mycoses?
A
- Blastomycosis
- Coccidioidomycosis
- Cryptococcosis
- Histoplasmosis
15
Q
Everything about pythiosis
A
- Etiopathogenesis
- aquatic, fungus-like water mold Pythium insidiosum
- Motile zoospores are infective
- Wound contamination - infested water
- Uncommon - dogs
- Rare - cats
- aquatic, fungus-like water mold Pythium insidiosum
- Clinical Signs:
- large, nonhealing, ulcerative granulomas on the limbs, ventrum or muzzle
- GI disease mor frequent
- Dx:
- Cytology & histopathology (biopsy)
- CUlture
- Serology (ELISA) - antibodies
- Tx:
- Wide surgical excision and possible limb amputation
- Antifungal therapy often unrewarding
- Pythium vaccine - curative in some cases
