Dermatology - Dermatophytosis Flashcards
What is dermatophytosis also known as?
Ringworm - Dr. Noxon said don’t call it that
What etiologic agents cause dermatophytosis?
Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes, Epidermophyton and other related organisms
All etiologic agents of dermatophytosis are zoophilic, except what?
M. gypseum
How is dermatophytosis transmitted?
by contact with infected animals, soil, or through fomites
What age of animals is more commonly affected by dermatophytosis?
younger animals
What are the predisposing factors of dermatophytosis?
poor nutrition, improper sanitation, immunosuppressive diseases, or use of glucocorticoids, and genetic factors
What is the pathogenesis of dermatophytosis?
- Dermatophytes invade and grow in non-viable keratinized tissue
- Grow only in hairs in anagen, weakening the hair shaft and causing it to break
- Incubation period of an average of 2 weeks
- Growing fungus advances down the hair follicle and releases metabolic by-products to incite an inflammatory reaction (folliculitus
- Type IV hypersensitivity reaction follows
- Fungus moves to a follicle nearby (outwards) creating a circular lesion
What are the classical lesions associated with dermatophytosis?
circular areas of alopecia, patchy alopecia with broken and brittle hair, erythema, hyperkeratinization and crusting, nodular hyperkeratotic erythematous lesions, mild-moderate pruritus may be reported
What classical lesions are associated with chronic dermatophytosis?
hyperpigmentation
Where are lesions due to dermatophytosis more frequently located?
the head, ears, and extremities
What do lesions of dermatophytosis caused by Trichophyton present as?
pustular eruptions
What may lesions may onchomycosis cause?
disortion and easily broken claws
What are pseudomycetomas?
deep dermal or subcutaneous infections by dermatophytes
How do pseudomycetomas present?
as nodules and draining lesions, that histologically are pyogranulomatous to granulomatous panniculitus
What is the causitive agent of pseudomycetomas in cats?
M. canis
What is the recommended treatment for pseudomycetomas?
surgical excision of the lesion and systemic antifungal therapy
What are the methods of diagnosis for dermatophytosis?
Clinical appearance, Wood’s light examination, trichogram, fungal culture, and/or skin biopsy
What differential diagnoses should be considered when considering dermatophytosis?
scaling disorders such as familial seborrhea, superficial pyoderma, demodicosis, hypothyroidism, and bacterial hypersensitivity
True or False: Wood’s light examination is a confirmatory test.
False, it is only a screening test
What should be examined when doing a Wood’s light examination?
the base of the plucked hairs
Which fungi that causes dermatophytosis is the only one that flouresces?
M. canis
What is a trichogram?
microscopic exam of hair and scrapings
Trichograms are an excellent screening test, ___ specificity, _____ sensitivity.
high, moderate
What is the most definitive diagnostic test for dermatophytosis?
a fungal culture
What samples should be used for a fungal culture?
broken hairs, crusts or scales, and/or individual hairs that fluoresce under the Wood’s light
Can you use alcohol on areas that you want to take a sample from for a fungal culture?
yes, it can cut down on contaminants
What is the MacKenzie Brush technique?
It is a technique that can be used to identify carrier animals - it employs a sterile toothbrush to comb the hair coat of the animal, the bristles are then imbedded or shaken over agar for culture
What is the standard fungal culture media?
Sabouraud’s dextrose agar
What should you be wary of when using dermatophyte test media?
Color change is not diagnostic - you should not base the diagnosis of the organism soley on the color change
How do M. canis colonies appear?
as white, fluffy coloniess
How do M. gypseum colonies appear?
generally cinnamon-buff in color with some white growth on the periphery
How do Trichophyton species colonies appear?
Produce a flat thallus that have a cream to yellowish-buff powdery surface
How does M. canis appear microscopically?
the macroconidiae have terminal knobs and usually have greater than 6 compartments
How does M. gypseum appear microscopically?
the macroconidiae have no knobs and up to 6 compartments
How does Trichophyton appear microscopically?
the macroconidiae are club-shaped and often hyphae are spiral shaped
What does histopathology from skin biopsies in dermatophytosis patients look like?
it shows folliculitis, furunculosis, keratinization abnormalities of the epidermis, fungal elements in keratinized layers
What therapies can be used to treat dermatophytosis?
Decontamination of the pet, topical therapies, systemic therapies, and decontamination of the environment
What is the goal of decontamination of a pet with dermatophytosis?
it is done to reduce the number of spores and infective hyphae
How is a pet decontaminated from dermatophytosis?
The hair is clipped around the lesion and topical disinfectants are used
What is Dr. Noxon’s favorite topical disinfectant?
miconazole-chlorhexidine shampoo
What other topical disinfectants can be used for decontamination of pets with dermatophytosis?
2% lime sulfur, 2-4% chlorhexidine rinses or shampoos, enilconazole rinses or spray, povidine-iodine shampoos
How often should topical disinfectants be used?
weekly if it is the sole therapy, otherwise done initially and then every 7-10 days if possible
When is topical dermatophytosis therapy used?
only on isolated lesions
When is topical therapy best/most effective?
when it is used in conjunction with systemic therapy
When is topical therapy not recommended as the sole treatment?
for multi-focal or generalized dermatophytosis
What are some topical therapy commercial products?
Conofite, Tinavet, Tresaderm, and Imaverol (in Canada)
What systemic treatments can be used to treat dermatophytosis?
Griseofulvin, Azoles, and Terbinafine
What is the recommended dosage and treatment plan for Griseofulvin?
Dosage is 25-50mg/kg of regular formation once daily orally
What enhances Griseofulvin absorption?
a high fat meal
How long should be Griseofulvin be given?
It should be given for 2 weeks beyond clinical remission (4-8 weeks is standard)
What formulation of Griseofulvin reduces the dosage in half?
ultrafine, microsized form
What side effects are associated with griseofulvin toxicities?
anorexia, vomiting, diarrhea, pruritic dermatoses, leukopenia (more likely in FIV-positive cats), and the drug is highly teratogenic during the first half of gestation
What azoles can be used for dermatophytosis treatment?
Ketoconazole, itraconazole, and fluconazole
What is the recommended treatment plan for ketoconazole?
10-30 mg/kg, orally once daily for 30-60 days
What adverse effects are associate with ketoconazole?
anorexia, alopecia, and increased hepatic enzyme concentrations
How is the drug Itraxonazole available?
capsules or liquid suspension (in cats)
What is the recommended treatment for Itraconazole?
Give it orally at 5-10 mg/kg PO daily for 30-60 days
Is generic or brand name Itraconazole recommended?
brand name - Sporanox
What is the recommended dosage for fluconazole?
5-10 mg/kg - there is no clear dosage
Which azole is the drug of choice for treatment of dermatophytosis in cats?
Itraconazole (Sporanox)
What is the overall drug of choice for systemic treatment of dermatophytosis in dogs and cats?
Terbinafine (Lamisil or generics)
What is the recommended treatment plan for Terbinafine?
10-30 mg/kg, orally, once daily for 4-6 weeks
Just an fyi (flip the card)
Terbinafine is not labeled for use in dogs and cats, however it is the drug of choice in dogs and cats…..
True or False: It is possible to sterilize the environment to remove all spores and hyphae
False - It is virtually impossible, the goal is to reduce the burden of infective agents in the house
What is the protocol if an animal tests positive for dermatophytosis in a cattery or a kennel?
Separate the infected animal immediately, wear protective clothing, clean and decontaminate the environment, and consider treating all animals with lufenuron (70mg/kg monthly for dogs and 100 mg/kg monthly for cats)
How is onychomycosis (infection of the claw) diagnosed?
by removing part or all of the claw and culture
Which systemic antifungals should not be given during pregnancy?
Griseofulvin, itraconazole, and fluconazole
What saprophytes are commonly isolated in dermatophytosis cases?
Alternaria spp., Mucor spp., Penicillium spp., Aspergillus spp., and Rhizopus spp.
