Fungal Skin Diseases Flashcards
If an infection is classed as superficial which skin layers does it affect?
Just the stratum corneum
If an infection is subcutaneous which skin layers does it affect?
Visible layers of the skin
Which skin layers do deep infection affect?
Internal organs > skin
What is dermatophytosis?
Infection of the hair, claw or stratum corneum with a fungus of the genera Microsporum/Trichophyton/Epidermophyton
How are dermatophytes classified?
Based on ecology
Zoophilic = higher animals (M.canis, T.mentagrophytes)
Geophilic = soil (M. gypseum)
Anthropophilic = human (T. rubrum, E. floccosum)
What is the aetiology of dermatophytosis?
Varies with hose species and geography
Species primarily affecting cats = M. canis
Species primarily affecting cattle = T. verrucosum
Species infecting horses = T. equinum, M. gypseum, M. canis
Main species affecting dogs = M. canis, T. mentag
What is the epidemiology of dermatophytosis?
Young animals are predisposed
High incidence of M. canis in Yorkshire Terriers and of sylvatic dermatophytosis in Jack Russels
Long haired cats are predisposed
No seasonal variation in incidence in the UK
What is the pathogenesis of dermatophytosis?
Contact with affected hair or squame Adherence of conidia to corneocytes Germination of spore Invasion between or through corneocytes of stratum corneum or hair Host inflammatory/immunological response
How can dermatophytosis present?
Circular/annular lesions with scaling, crusts, erythema or alopecia
Diffuse scaling
Nodules/uceration
Asymptomatic carriers
What does sylvatic dermatophytosis often present as in dogs?
Folliculitis or furunculosis
How is dermatophytosis diagnosed?
Skin scrapings/hair plucks
Wood’s Lamp (only Microsporum)
Fungal culture
Skin biopsies
How do you use Wood’s Lamp?
Darkened room, lamp warmed up
Shine lamp over haircoat
Apple-green fluorescence of hair
50% of M canis strains induce fluorescence
What is the procedure for getting a sample for culture of dermatophytosis?
Select broken hairs/scales/crusts
Pluck hairs and pull off scales with forceps and or scrap with a dry blade
Place in a universal container or envelope
Submit to laboratory
How is dermatophytosis cultured?
Sabourauds dextrose agar with cycloheximide and chloramphenicol
Incubate at 26C for up to 4 weeks
Assess colonies and microscopic features
Ideally used a reputable mycology laboratory
What is a dermatophyte test medium?
SDA plus phenol red indicator and as dermatophytes utilise protein they produce alkaline metabolites resulting in red colour
Early colour change plus white colony suggests a dermatophyte is present
