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Dermatology > Dermatophytosis > Flashcards

Dermatophytosis Flashcards

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Dermatology Board Prep flashcards
1
Q

What are the most common dermatophytes that affect dogs and cats?

A
  • Microsporum canis
  • Microsporum gypseum
  • Trichophyton mentagrophytes
  • Microsporum persicolor
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2
Q

What are the most common dermatophytes that affect horses?

A
  • Trichophyton equinum
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3
Q

What are the most common dermatophytes that affect cattle?

A
  • Trichophyton verrucosum
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4
Q

What are the most common dermatophytes that affect pigs?

A

Microsporum nanum

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5
Q

What is the reservoir for Microsporum canis?

A

cats

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6
Q

What is the reservoir for Microsporum gypseum?

A

soil

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7
Q

What is the reservoir for T. mentagrophytes?

A

rodents, rabbits, pocket pets

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8
Q

What are the predisposing factors for dermatophytosis?

A
  • lack/decreased grooming
  • presence of microtrauma
  • excessive hydration/maceration
  • warm temp and humidity
  • lack of sun exposure
  • strong cell-mediated immunity
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9
Q

What are the breed and age predispositions in dogs and cats for dermatophytosis?

A
  • Breeds:
    • white Persians and Himalayan
      • asymptomatic carriers
    • terriers
  • Age:
    • young animals are predisposed
    • sick and emaciated animals are predisposed
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10
Q

What are the cutaneous signs of dermatophytosis in dogs and cats?

A
  • Extremely variable
    • always included in differentials for cats
  • absent to moderate pruritus
  • erythema/alopecia
  • crusting/scaling/pustules
  • miliary dermatitis (cats)
  • dermal nodules/plaques
  • muzzle and feet most affected
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11
Q

What are the cutaneous signs of dermatophytosis in horses?

A
  • most common dermatophyte = T. equinum
  • direct and indirect transmission
    • infected tack and grooming equipment
  • follicular pustules
  • variable sized annular alopecic areas
  • severe scaling, crusting, pustules, ulcers, pruritus
  • saddle and tack regions
  • urticaria-like lesions
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12
Q

What are the cutaneous signs of dermatophytosis in cattle?

A
  • Most comomon dermatophy = T. verrucosum
  • most common in confined cattle
  • circular, alopecic areas
  • severe scaling, crusting, and suppuration
  • pain and pruritus - variable
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13
Q

Describe kerion

A

a well-circumscribed nodular mass

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14
Q

What are your differentials for dermatophytosis?

A
  • parasitic dz
  • allergies
  • pemphigus foliaceus
  • keratinization defects
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15
Q

Describe the Wood’s lamp diagnostic test

A
  • positive in 50% of M. canis/equinum strains
    • Tryptophan metabolites
  • good screening test
  • NON-specific!
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16
Q

How do you diagnose dermatophytosis?

A
  • Clinical approach: hx and PE
  • Diagnostics:
    • Wood’s lamp
    • Trichogram (hair pluck)
    • Fungal culture
    • Skin biopsy/histopathology
17
Q

Describe the Trichogram diagnostic test

A
  • mineral oil
  • KOH/NaOH preparation
  • microscope setting
    • low condenser
    • low light
    • low objective
18
Q

How should you store fungal cultures and how often should you check them?

A
  • upside-down
  • in the dark
  • room temp: 30 degrees C
  • check daily
19
Q

What is the MacKenzie technique?

A
  • useful for feline asymptomatic carriers
  • use collected hairs from bristles or cut bristles and place them onto media
20
Q

What stains should you use for tape preps?

A
  • Lactophenol Cotton Blue
  • Polychromatic Multiple Stain
21
Q

What are three important principles in treatment of both small and large animal infections?

A
  • elimination of infection from host
  • prevention of further dissemination of infective spores
    • spores can survive up to 18 mo
  • removal of infective spores already in the environment

*healthy animals can self-cure in 12-17 wks

22
Q

What are you therapeutic options for dermatophytosis?

A
  • systemic tx
  • topical tx
  • environmental tx

treat ALL in contact with animals!

23
Q

What are options for topical therapy?

A
  • Ketoconazole
  • Miconazole
  • Chlorhexidine
  • Lyme sulfur
24
Q

How often should rinses be performed for dermatophytosis treatment?

A

twice weekly

  • lime sulfur dips
  • enilconazole
    • ^ these two dry hair coat
  • accelerated hydrogen peroxide rinse
25
Q

What are examples of systemic therapy for dermatophytoses?

A
  • Ketoconazole
  • Itraconazole
  • Fluconazole
  • Terbinafine
  • Griseofulvin
26
Q

Describe griseofulvin

A
  • fungistatic
  • very cheap
  • variable oral absorption
    • incr fatty meal
    • particle size
      • microsize and ultramicrosize
    • presence of polyethylene glycol
  • only effective against dermatophytes
27
Q

What are the side effects of griseofulvin?

A
  • vomiting
  • diarrhea
  • anorexia
  • bone marrow suppression
  • Siameses, Himalayans, and Abyssinians
  • Monitor CBC, FIV, FeLV and other viruses
  • teratogenic
28
Q

Describe ketoconazole

A
  • Fungistatic
    • Ergosterol synthesis in fungal cell wall
  • Good oral absorption
    • incr fatty meal
    • decr non-acid gastric environment
      • H2 antagonists
    • good efficacy against M. canis, T. mentagrophytes, and Malassezia spp.
29
Q

What are the side effects of ketoconazole?

A
  • vomiting, diarrhea, and anorexia
  • incr liver enzymes
  • interfer w/ steroid synthesis and inhibtion of cytochrome p450 enzymes
    • check for drug interactions
  • dogs: tolerate ketoconazole fairly well
  • cats: anorexia, even at lower dose
  • contraindicated in pregnant animals
30
Q

Describe itraconazole

A
  • fungistatic (low dose)/fungicidal (high dose)
  • preferred choice for feline fungal infections
  • good oral absorption
    • incr fatty meal
  • very expensive
    • residual effect
      • accumulation in keratinized tissues
  • formultions:
    • capsules
    • oral suspension
31
Q

What are the side effects of itraconazole?

A
  • uncommon
  • GI upset and hepatotoxicity (rarely)
  • reversible, dose-dependent cutaneous vasculitis in dogs at higher doses, anorexia
  • mild inhibition of the cytochrome p450
  • not rx in pregnant animals
    • potential for teratogenicity and embriotoxicity
32
Q

Describe fluconazole

A
  • Fungistatic
  • bis-triazole antifungal
  • expensive
  • broad antimycotic spectrum
  • side effects appear uncommon
    • GI upset
  • little hepatic metabolism
    • mild inhibition of the cytochrome p450
  • Rx in patients w/ hepatic dz
33
Q

Describe terbinafine

A
  • Allylamine derivative
    • inhibits squalene epoxidase and prevent ergosterol synthesis
      • fungicidal
  • residual effect
    • accumulates in keratinized tissues
  • very few side effects
    • vomiting and facial pruritus (cats)
    • incr liver enzymes
  • no inhibition of cytochrome P450
34
Q

Describe immunotherapy for dermatophytoses

A
  • Killed M. canis in cats licensed for prevention and treatment of lesions, but NOT the dz
  • NO efficacy in preventing or providing rapid cure when compared with untreated controls
    • slightly decr severity of initial infection compared w/ controls
  • large animals (cattle)
    • considerable success in prophylactic or therapeutic use
35
Q

Describe environmental decontamination for dermatophytoses

A
  • water and bleach
    • repeat the wash twice in a washing machine
  • any materials that cannot be effectively treated should be discarded
  • concentrated bleach and 1% formalin are 100% effective
    • ​toxicity
  • 1:10 to 1:100 bleach, 1:33 lime-sulfur, and 0.2% enilconazole
36
Q

Describe the triple cleaning technique

A
  • Mechanically removed spores and hairs
    • vacuuming and using Swiffer cloths
  • Wash and rinse surfaces 3x
    • detergent solution
  • Disinfect target areas w/ 1:10 bleach
    • Twice weekly using this protocol
    • Homes were culture negative after one to three cleanings!
37
Q

For what duration should your therapy last for dermatophytoses?

A
  • therapy should include: topical, systemic, and environmental tx
  • no growth on two sequential weekly cultures
    • ​finalized after 14d
      • suggested to keep the cultures for 21d
  • 2 neg cultures 1 mo apart
38
Q

What is the treatment for onychomycosis?

A
  • prognosis for cure is guarded and will take several months (6-12+) if at all
  • itraconazole and terbinafine are probably best agents for use
    • residual effect
  • onychectomy may be indicated for resistant/recalcitrant cases or financial concerns
39
Q

Describe dermatophytoses therapies for large animals

A
  • Infections usually self-limiting
  • treatment goals:
    • shorten course of dz
    • limit spread to other animals and humans
    • prevent dissemination into environment
  • good preventative medicine program is important part of tx
  • systemic tx = rarely indicated
  • topical tx: lime sulfur spray
  • treat 2 wks past clinical cure
  • separate infected animals
  • environmental decontamination
  • decr crowding, incr UV light exposure

Dermatology (13 decks)

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