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Flashcards in Fungal Diseases Deck (20)
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What is dermatophytosis? What is this commonly called?

- ringworm
- infection of hair, nail or stratum corneum by fungus of genera..
> micropsorum
> trichopython
> epidermophyton
- digest keratinous tissues not living tissues


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


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


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


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)


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


Clinical signs of dermatophytosis in horses?

- patches of scale and hairloss esp. in contact with tack


Clinical signs of dermatophytosis in cattel

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


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)


Should dermatophytois be treated?

- cases are self limiting BUT zoonotic potential -> ALWAYS TX.


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)


Tx dermatophytosis in large animals

- topical tx with enilconazole or Malaseb
- disinfect tack
- Boviliv Ringvac in cattle preventative vax


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

- dogs
- malassezia


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


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


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)


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


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


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

- Candida
(malasezia and dermatophytoisis also superficial)


Do any fungi affect deeper layers of skin?

- 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"