Flashcards in Fungal Diseases Deck (20)
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What is dermatophytosis? What is this commonly called?
- 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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Aetiology of dermatophytosis?
- 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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Pathogenesis of dermatophytosis?
-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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Historical features of dermatophytosis?
- 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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Clinical signs of dermatophytosis in dogs?
- 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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Clinical signs of dermatophytosis in cats?
- 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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Clinical signs of dermatophytosis in horses?
- patches of scale and hairloss esp. in contact with tack
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Clinical signs of dermatophytosis in cattel
focal patches thick grey scales or crust with alopecia, especially on head
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Diagnostic techniques for dermatophytosis?
> 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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Should dermatophytois be treated?
- cases are self limiting BUT zoonotic potential -> ALWAYS TX.
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Tx dermatophytosis in smallies
> 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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Tx dermatophytosis in large animals
- topical tx with enilconazole or Malaseb
- disinfect tack
- Boviliv Ringvac in cattle preventative vax
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Which species is most commonly affected by m. pachydermatis? What yeast is this?
- dogs
- malassezia
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What is m. pachydermatis?
- 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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Pathogenesis of m. pachydermatis?
- 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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Clinical signs of malassezia dermatitis?
- 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)
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Diagnosing malassezia dermatitis?
- ^ m. pachydermatis on lesions
- clinical response to antifungals
- mycological response to antifungals
> tape strip, direct smear, culture, biopsy? low sensitivity
> cytology
> culture
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Tx malasezzia dermatitis
- 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
Which yeast also causes superficial dermatitis but is more of a problem in humans than dogs?
- Candida
(malasezia and dermatophytoisis also superficial)
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