Derm 6 - fungal

Question 1

Mycoses are divided into 3 categories:

Answer 1

superficial, subcutaneous, systemic

Question 2

superficial, subcutaneous, systemic
- which tissues are involved in each category

Answer 2

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

Question 3

superficial mycoses

Answer 3

• Dermatophytosis
• Malassezia Dermatitis
• Candidiasis

Question 4

subcutaneous mycoses

Answer 4

• Sporotrichosis
• Dermatophytic pseudomycetoma
• Eumycotic Mycetoma
• Phaeohyphomycosis
• Pythiosis
• Lagenidiosis
• Zygomycosis

Question 5

systemic / deep mycoses

Answer 5

• Cryptococcosis
• Blastomycosis
• Coccidiomycosis
• Histoplasmosis

Question 6

Dermatophytosis
- affects who?
- transmission

Answer 6

• 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

Question 7

Dermatophytosis most common isolates, and how they are transmitted, defining characteristics

Answer 7

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

Question 8

dermatophytosis transmission - general and M. canis

Answer 8

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

Question 9

dermatophytosis pathogenesis

Answer 9

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

Question 10

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?

Answer 10

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

Question 11

ringworm carrier breeds for cats and dogs

Answer 11

o Persians and Himalayans can be asymptomatic carries
o Yorkshire Terriers are the “Persians of the dog world” when it comes to ringworm

Question 12

dermatophytosis in dogs
- lesion appearance:

Answer 12

• 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

Question 13

dermatophytosis in dogs breed dyspositions

Answer 13

 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

Question 14

dermatophytosis in cats
- mostly what species of fungus?
- clinical signs?
- who more commonly gets clinical signs?

Answer 14

 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

Question 15

dermatophytic pseudomycetoma in cats - what is this? what fingus and what type of cats?

Answer 15

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

Question 16

what is wood’s lamp? what is its use?

Answer 16

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

Question 17

dermatophytosis diagnosis options

Answer 17

• Wood’s lamp
• Direct microscopic exam
• Fungal Culture
• Histopathology
• PCR

Question 18

drawbacks of PCR for fungal diagnosis

Answer 18

– 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.

Question 19

dermatophytosis treatment length, and elements (3)

Answer 19

 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

Question 20

when do cats need systemic vs topical therapy for dermatophytosis?

Answer 20

 all cats should receive systemic and topical therapy

Question 21

when should dogs receive systemic vs topical therapy for dermatophytosis?

Answer 21

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

Question 22

topical treatments for dermatophytosis
- what should we do, and why?

Answer 22

• 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
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• 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

Question 23

systemic treatment options for dermatophytosis?
- which is drug of choice for cats?
> something we should not do with this drug?

Answer 23

• Itraconazole
  > DO NOT USE COMPOUNDED ITRACONAZOLE as they typically have poor bioavailability
• fluconazole
  > less effective vs itraconazole
• terbafine

Question 24

environmental control of dermatophytosis - primary aim

Answer 24

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)

Question 25

is environmental contamination alone often enough to cause dermatophyte infection?

Answer 25

contact with a contaminated environment alone in the absence of concurrent microtrauma is an exceedingly rare source of infection in both people and animals