Derm 6 - fungal Flashcards
Mycoses are divided into 3 categories:
superficial, subcutaneous, systemic
superficial, subcutaneous, systemic
- which tissues are involved in each category
SUPERFICIAL:
- skin, hair, claws
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SUBCUTANEOUS:
- skin, subcutis
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SYSTEMIC/DEEP
- affect internal organs with hematogenous spread to skin
superficial mycoses
- Dermatophytosis
- Malassezia Dermatitis
- Candidiasis
subcutaneous mycoses
- Sporotrichosis
- Dermatophytic pseudomycetoma
- Eumycotic Mycetoma
- Phaeohyphomycosis
- Pythiosis
- Lagenidiosis
- Zygomycosis
systemic / deep mycoses
- Cryptococcosis
- Blastomycosis
- Coccidiomycosis
- Histoplasmosis
Dermatophytosis
- affects who?
- transmission
- Zoonosis - Client education important!
o Causes skin lesions that are treatable and curable. Contagious to humans and animals but the true rate
of transmission is unknown. Humans and animals with weakened immune systems are more compromised and should avoid contact (most common complication of Microsporum canis infection in immunocompromised people is prolonged treatment time)
o Ringworm can be transmitted by direct contact with infected hairs and skin scales from other humans or animals, in the environment, or on fomites such as bedding, crates, brushes and other grooming equipment
Dermatophytosis most common isolates, and how they are transmitted, defining characteristics
Microsporum canis:
most common in dogs and cats
well adapted to the cat
most likely to spread from cat to cat, cat to dog, cat to human
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Microsporum gypseum complex
contracted from soil
less contagious
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Trichophyton Mentagrophytes complex
contracted from rodents and their environments
proteolytic enzymes that can induce acantholysis, mimicking pemphigus foliaceus
dermatophytosis transmission - general and M. canis
o Contact with infected hair, scales, fungal elements on animals, environment (soil) or fomites
o M. canis cultured from dust, heating vents, furnace filters (arthrospores remain infectious for up to 18
months)
o M. canis cultured from on a cat may be infection (with clinical signs), asymptomatic carrier or
passive/mechanical carriage
o Mechanical disruption of stratum corneum may be important in facilitating penetration and invasion of anagen hair follicles
dermatophytosis pathogenesis
o Type IV hypersensitivity reaction
o Arthrospores infective and adhere strongly to keratin
o Trauma/mechanical disruption of skin facilitates penetration
o Fungal hyphae invade the hair follicle of anagen hairs and migrate downwards
o Fungal metabolic by-products incite an inflammatory reaction, inducing folliculitis which may lead to
furunculosis (rupture of the hair follicle)
o Spontaneous resolution occurs when hairs enter telogen (keratin production stops) or if inflammatory reaction
incited
Clinical course: Experimental models: Inoculate cats with M. canis:
- incubation period
- when are lesions enlarged?
- when do lesions resolve?
- how long after clinical resolution can we get a + test?
- how long for spontaneous resolution?
o 7-14 d incubation
o lesions enlarged 6-8wks
o lesions resolve 14-18 weeks
o toothbrush +ve 1-2 wks. after clinical resolution
o spontaneous resolution 2.5-3 months
ringworm carrier breeds for cats and dogs
o Persians and Himalayans can be asymptomatic carries
o Yorkshire Terriers are the “Persians of the dog world” when it comes to ringworm
dermatophytosis in dogs
- lesion appearance:
- lesions are very variable but can include:
Classic annular lesion
Patchy alopecia, erythema, scale, crust
Folliculitis and furunculosis (follicular papules and pustules)
Onychomycosis, pododermatitis (most often T. mentagrophytes)
Superficial neutrophilic pustules, sometimes with acantholysis
> Can mimic pemphigus foliaceus and pyoderma (most cases are T.mentagrophytes)
Symmetric nasal or facial folliculitis and furunculosis
Kerion: alopecic, dome-shaped exudative nodules
dermatophytosis in dogs breed dyspositions
Breed predisposition: Fox Terrier, Manchester Terrier, Bull Terrier
Yorkshire Terriers have a severe form of M.canis (most have concurrent disease causing reduced CMI response).
They can also be asymptomatic carriers
dermatophytosis in cats
- mostly what species of fungus?
- clinical signs?
- who more commonly gets clinical signs?
90% M. canis
asymptomatic carriers common
lesions more common in kittens, long-haired/Persian cats
nonpruritic to markedly pruritic
face and pinna predisposed
irregular or annular areas of alopecia with or without scales
widespread alopecia with little inflammation
inflammatory folliculitis with alopecia, erythema, scale, crust, follicular papules
hyperpigmentation (often not seen with other feline dermatoses)
widespread exfoliative erythroderma
may be cause of any of reaction patterns:
> miliary dermatitis
> eosinophilic plaques
> eosinophilic ulcer
> symmetrical alopecia
recurring chin folliculitis
dermatitis of dorsal tail resembling “stud tail”
onychomycosis and kerions rare in cats
dermatophytic pseudomycetoma
o deeper dermal and/or subcutaneous infection
o most commonly M. canis
o reported only in Persian cats
o one or more subcutaneous ulcerated, fistulated nodules (1-8cm)
o +/- superficial dermatophyte lesions on other areas of body
o pathogenesis: unclear, possible direct invasion of dermal tissues by rupture of follicular structures
dermatophytic pseudomycetoma in cats - what is this? what fingus and what type of cats?
o deeper dermal and/or subcutaneous infection
o most commonly M. canis
o reported only in Persian cats
o one or more subcutaneous ulcerated, fistulated nodules (1-8cm)
o +/- superficial dermatophyte lesions on other areas of body
o pathogenesis: unclear, possible direct invasion of dermal tissues by rupture of follicular structures
what is wood’s lamp? what is its use?
Wood’s lamp:
M. canis fluoresces an apple green colour on the hair shafts. The part that fluoresces is a water soluble chemical metabolite called pteridine that is a result of the infection and not specifically associated with the spores or infective material themselves. It is usually present by 10-14 days post infection. As the hair continues to grow out in a treated cat, the fluorescence will move distally along the shaft. Woods lamp examination should be considered to be a screening test only and does not replace the need for culture but is helpful to decide which
hairs to collect for fungal culture
dermatophytosis diagnosis options
- Wood’s lamp
- Direct microscopic exam
- Fungal Culture
- Histopathology
- PCR
drawbacks of PCR for fungal diagnosis
– remember that a positive PCR can be a result of an active infection but can also be due to fomite
carriage or a nonviable organism in a successfully treated patient. It is also important to be sure that there are adequate quality control measures in the chosen laboratory.
dermatophytosis treatment length, and elements (3)
4-20 weeks of therapy
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3 elements of treatment:
a. topical therapy: faster improvement, reduces environmental contamination
b. systemic therapy:
reduces time to complete cure
all cats should receive systemic and topical therapy
dogs should require systemic and topical therapy if: multifocal lesions, long-haired,
immunocompromised, Trichophyton spp is cultured, multiple animal households, or if not
responding to topical therapy after 2-4 weeks
c. environmental control: reduces spread
when do cats need systemic vs topical therapy for dermatophytosis?
all cats should receive systemic and topical therapy
when should dogs receive systemic vs topical therapy for dermatophytosis?
dogs should require systemic and topical therapy if:
- multifocal lesions,
- long-haired,
- immunocompromised,
- Trichophyton spp is cultured,
- multiple animal households,
- or if not responding to topical therapy after 2-4 weeks
topical treatments for dermatophytosis
- what should we do, and why?
- clipping of hair coat
reduces fragile hairs that will break and spread spores
improves topical therapy penetration
shorthaired animals with <5 focal lesions should not be clipped
long haired cats or dogs with more than 5 focal lesions, generalized lesions, concurrent skin or
systemic disease should be clipped
#10 blade
may temporarily exacerbate lesions, avoid traumatizing skin
careful disposal of hairs/ disinfection of blade - twice weekly rinse or shampoo - miconazole + chlorhexidine (synergistic) shampoo
<><><><> - lime-sulfur 2% dips (not available commercially in Canada – would need to be compounded)
- enilconazole (Imaverol) therapy (not currently available)
> salivation, anorexia, weight loss, emesis, muscle weakness, increased ALT in cats- use e-collar till dries - spot treatment not recommended
systemic treatment options for dermatophytosis?
- which is drug of choice for cats?
> something we should not do with this drug?
- Itraconazole
> DO NOT USE COMPOUNDED ITRACONAZOLE as they typically have poor bioavailability - fluconazole
> less effective vs itraconazole - terbafine
environmental control of dermatophytosis - primary aim
to shorten the course of treatment by preventing/minimizing false positive fungal culture or PCR results due to fomite carriage of spores on the hair coat (false positive fungal culture results
> lead to prolonged systemic and/or topical therapy and excessive confinement of pets)
is environmental contamination alone often enough to cause dermatophyte infection?
contact with a contaminated environment alone in the absence of concurrent microtrauma is an exceedingly rare source of infection in both people and animals
