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Dermatology > Fungal Diseases > Flashcards

Fungal Diseases Flashcards

0
Q

Aetiology of dermatophytosis?

A
  • spp of interest differ geographically and depending on host
    > UK microsporum canis 90% feline, 60% canine
    > Trichophyton mentogrophytes 30% canine
    > T. verrucosum cattle and sheep
    > T. equiinum and M. equinum horses
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1
Q

What is dermatophytosis? What is this commonly called?

A
  • ringworm
  • ZOONOTIC
  • infection of hair, nail or stratum corneum by fungus of genera..
    > micropsorum
    > trichopython
    > epidermophyton
  • digest keratinous tissues not living tissues
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2
Q

Pathogenesis of dermatophytosis?

A

-contact with infected animals, soil or fomites
- commonest source for dogs is infected cats
- trichophyton spp. wild rodent carriers
- M. canis spores remain viable for >1yr
> skin invasion by adherance of arthrospores to stratum corneum
> spores germinate, hyphae invade stratum corneum
> penetrate hair shafts in anagen
- do not invade mitotically active hair matrix
> invasion of keratinised tissues, production of fungal enzymes -> inflammaotry response
> resolution of diseasse within 1-3months
> chronic disease results if animals immunosuppressed

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3
Q

Historical features of dermatophytosis?

A
  • progressive skin disease
  • spread initially from point focus
  • hx contact with wild rodents and cats
  • hx of disease on farmn
  • owner lesions
  • degree of pruritis variable
  • < 1 year
  • long haired cats prediosposed
  • jack russells predisposed to trichopyton
  • yorkshire terriers predisposed to m. canis infection
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4
Q

Clinical signs of dermatophytosis in dogs?

A
  • highly variable
  • localised disease
  • ringworm lesions most common (focal area alopecia and scaling, expands and heals centrally)
  • may be multiple lesions but be aware most comon cause of multiple lesions is bacterial infectio
  • OR localised folliculitis and furunculitis well demarcated (ddx autoimmune disease)
  • OR local/generalisd scaling +- erythematous margin, healing area smooth and shiny
  • OR oncomycosis (nail infection) +- paronychia (nail fold infection)
  • OR kerion (nodular, deep suppurant inflam lesions)
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5
Q

Clinical signs of dermatophytosis in cats?

A
  • any of dogs presentations
  • most commonly irregular, patchy alopecia +- scaling
  • OR ulcerating nodules with granulomatous perifolliculitis (dermatophytic pseudomycetoma in Persians)
  • OR papulocrustuous eruption (miliary dermatitis)
  • OR recurrent chin acne
  • OR clinically normal carriers
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6
Q

Clinical signs of dermatophytosis in horses?

A
  • patches of scale and hairloss esp. in contact with tack
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7
Q

Clinical signs of dermatophytosis in cattel

A

focal patches thick grey scales or crust with alopecia, especially on head

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9
Q

Diagnostic techniques for dermatophytosis?

A

> microscopy
fluorescence microscopy (calcafluor white binds to dermatophyte cell walls but need UV microscope ; rare)
woods lamp exam (HAIRS fluoresce in 50% of cases, cannot be dismissed if negative as many dermatophytes DO NOT FLUORESCE)
culture (Sabarauds dextrose agar, aerobic, 4 weeks - flat white colonies adn red colour change)
Biopsy (demonstrate fungal hyphal invasion of skin biopsy specimens - definitive dx)

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10
Q

Should dermatophytois be treated?

A
  • cases are self limiting BUT zoonotic potential -> ALWAYS TX.
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11
Q

Tx dermatophytosis in smallies

A

> clip hair
systemic antifungals
- azoles (itraconazole, LIC cats one week on/one off)
- griseofulvin no longer LIC (teratogenic, haem effects, tx would be -> 2 weeks after cure)
topical antifungals (do not penetrate hair so unlikely to shorten disease BUT v environmental contamination)
- Enilconazole [Imaverol] (LIC dogs, q3d; fatal idiosyncratic reactions in cats)
- miconazole + chlorhexidine [Malaseb shampoo] (LIC cats, good dogs too)

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12
Q

Tx dermatophytosis in large animals

A
  • topical tx with enilconazole or Malaseb
  • disinfect tack
  • Boviliv Ringvac in cattle preventative vax
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13
Q

Which species is most commonly affected by m. pachydermatis? What yeast is this?

A
  • dogs

- malassezia

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14
Q

What is m. pachydermatis?

A
  • monopolar budding yeast
  • commensal of skin and mucosa healthy dogs (and cats a bit)
  • pathogenic levels ofen associated with ^ pathogenic staph
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15
Q

Pathogenesis of m. pachydermatis?

A
  • liberates enzymes and metabolites -> cutaneous inflammation
  • hypersensitivity to pathogen may be seen
  • concurrent skin disease found in > half cases (eg. atopic dermatitis and 1* keratinisation defects)
  • basset hounds, cocker spaniels and westies predisposed
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16
Q

Clinical signs of malassezia dermatitis?

A
  • complication or mimicing of allergic skin disease and scaling/crusting disorders
  • highly pruritic and refrctory to abx, steroids and parasiticidals
  • erythema (+- alopecia and scaling)
  • greasy exudate in folded areas
  • hyperpigmentation and lichenification if chronic
  • ventral neck, interdigital skin, axillae and groin
  • concurrent erythematous otitis externa and ceruminous discharge common
    > frenzied facial pruritis = uncommon manifestation, collapse when face is stroked (ddx neuro)
17
Q

Diagnosing malassezia dermatitis?

A
  • ^ m. pachydermatis on lesions
  • clinical response to antifungals
  • mycological response to antifungals
    > tape strip, direct smear, culture, biopsy? low sensitivity
    > cytology
    > culture
18
Q

Tx malasezzia dermatitis

A
  • v bacterial and yeast counts
  • ID and tx correct underlying factors
  • Malaseb shampoo q3d or until controlled then v
  • selenium sulphide, ketoconazole/chlorhex shampoos
  • Enilconazole rinse (Imaverol)
    > systmeic tx with ketoconazole/itraconazole = efficient but $$$ and not LIC, potential hepatotoxicity
19
Q

Which yeast also causes superficial dermatitis but is more of a problem in humans than dogs?

A
  • Candida

malasezia and dermatophytoisis also superficial

20
Q

Do any fungi affect deeper layers of skin?

A
  • subcutaneous and systemic mycoses affect the deeper layers
  • rare/absent in the UK
    > cryptococcus neoformans may be seen in cats (nodular granulomatous + resp lesions)
    > histoplasmosis, blastomycosis and coccioidomycosis systemic mycoses seen in USA
    > sporotrichosis transmissable to man
  • sparophytic fungi induce granulomatous inflammation if traumatically implanted into the skin -> “Mycetoma”

Dermatology (25 decks)

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