Dermatophytosis Flashcards
What are the most common dermatophytes that affect dogs and cats?
- Microsporum canis
- Microsporum gypseum
- Trichophyton mentagrophytes
- Microsporum persicolor
What are the most common dermatophytes that affect horses?
- Trichophyton equinum
What are the most common dermatophytes that affect cattle?
- Trichophyton verrucosum
What are the most common dermatophytes that affect pigs?
Microsporum nanum
What is the reservoir for Microsporum canis?
cats
What is the reservoir for Microsporum gypseum?
soil
What is the reservoir for T. mentagrophytes?
rodents, rabbits, pocket pets
What are the predisposing factors for dermatophytosis?
- lack/decreased grooming
- presence of microtrauma
- excessive hydration/maceration
- warm temp and humidity
- lack of sun exposure
- strong cell-mediated immunity
What are the breed and age predispositions in dogs and cats for dermatophytosis?
- Breeds:
- white Persians and Himalayan
- asymptomatic carriers
- terriers
- white Persians and Himalayan
- Age:
- young animals are predisposed
- sick and emaciated animals are predisposed
What are the cutaneous signs of dermatophytosis in dogs and cats?
- 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
What are the cutaneous signs of dermatophytosis in horses?
- 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
What are the cutaneous signs of dermatophytosis in cattle?
- Most comomon dermatophy = T. verrucosum
- most common in confined cattle
- circular, alopecic areas
- severe scaling, crusting, and suppuration
- pain and pruritus - variable
Describe kerion
a well-circumscribed nodular mass
What are your differentials for dermatophytosis?
- parasitic dz
- allergies
- pemphigus foliaceus
- keratinization defects
Describe the Wood’s lamp diagnostic test
- positive in 50% of M. canis/equinum strains
- Tryptophan metabolites
- good screening test
- NON-specific!
How do you diagnose dermatophytosis?
- Clinical approach: hx and PE
- Diagnostics:
- Wood’s lamp
- Trichogram (hair pluck)
- Fungal culture
- Skin biopsy/histopathology
Describe the Trichogram diagnostic test
- mineral oil
- KOH/NaOH preparation
- microscope setting
- low condenser
- low light
- low objective
How should you store fungal cultures and how often should you check them?
- upside-down
- in the dark
- room temp: 30 degrees C
- check daily
What is the MacKenzie technique?
- useful for feline asymptomatic carriers
- use collected hairs from bristles or cut bristles and place them onto media
What stains should you use for tape preps?
- Lactophenol Cotton Blue
- Polychromatic Multiple Stain
What are three important principles in treatment of both small and large animal infections?
- 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
What are you therapeutic options for dermatophytosis?
- systemic tx
- topical tx
- environmental tx
treat ALL in contact with animals!
What are options for topical therapy?
- Ketoconazole
- Miconazole
- Chlorhexidine
- Lyme sulfur
How often should rinses be performed for dermatophytosis treatment?
twice weekly
- lime sulfur dips
- enilconazole
- ^ these two dry hair coat
- accelerated hydrogen peroxide rinse
What are examples of systemic therapy for dermatophytoses?
- Ketoconazole
- Itraconazole
- Fluconazole
- Terbinafine
- Griseofulvin
Describe griseofulvin
- fungistatic
- very cheap
- variable oral absorption
- incr fatty meal
- particle size
- microsize and ultramicrosize
- presence of polyethylene glycol
- only effective against dermatophytes
What are the side effects of griseofulvin?
- vomiting
- diarrhea
- anorexia
- bone marrow suppression
- Siameses, Himalayans, and Abyssinians
- Monitor CBC, FIV, FeLV and other viruses
- teratogenic
Describe ketoconazole
- 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.
What are the side effects of ketoconazole?
- 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
Describe itraconazole
- 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
- residual effect
- formultions:
- capsules
- oral suspension
What are the side effects of itraconazole?
- 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
Describe fluconazole
- 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
Describe terbinafine
- Allylamine derivative
- inhibits squalene epoxidase and prevent ergosterol synthesis
- fungicidal
- inhibits squalene epoxidase and prevent ergosterol synthesis
- residual effect
- accumulates in keratinized tissues
- very few side effects
- vomiting and facial pruritus (cats)
- incr liver enzymes
- no inhibition of cytochrome P450
Describe immunotherapy for dermatophytoses
- 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
Describe environmental decontamination for dermatophytoses
- 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
Describe the triple cleaning technique
- 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!
For what duration should your therapy last for dermatophytoses?
- 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
-
finalized after 14d
- 2 neg cultures 1 mo apart
What is the treatment for onychomycosis?
- 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
Describe dermatophytoses therapies for large animals
- 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
