Fungal Causes of Skin Disease Flashcards
Types of fungi which cause skin disease
Commensals
* Malassezia
Transient contaminants
* Environmental saprophytes
* Sometimes dermatophytes
Active pathogens
* Dermatophytes
How do fungi cause skin disease?
Mycoses
Superficial
Deep
Systemic
Hypersensitivity
Dermatophytosis
‘Ringworm’
Caused by dermatophytic fungi
* Trichophyton spp.
* Microsporum spp.
Contagious
Zoonotic!
Geophilic
Adapted for environment
Zoophilic
Adapted for mammals
Most common source of animals disease
Anthropophilic
Adapted for man
Stages of dermatophytosis infections
- Skin microtrauma and moisture
- Inoculation and germination of infective arthrospores
- Germ tubes penetrate start corneum
- Growth of fungal hyphae
- Lesions within 5-7 days
What species is dermatophytosis common in?
Cow
Horse
Cat
Sometimes dog
Zoonotic to humans
Clinical signs of dermatophytosis
Alopecia
Folliculitis
Patchy, multifocal, well-demarcated circular grey lesions
Scale and crust
Variable pruritus
Affects haired skin
Uncommon presentation of dermatophytosis
Furunculosis
Fungal Kerion
Pseudomycetoma
Onychomycosis
Furunculosis
Deep infection of hair follicle
Rupture of follicle wall
Accumulation of purulent material and necrotic tissue
Looks similar to deep pyoderma
Fungal Kerion
○ Nodular inflammatory mass due to inoculation of fungus into dermis
○ Especially hunting/working dogs
Pseudomycetoma
○ Subcutaneous/deep mycosis
○ Nodular granulomas
○ +/- ulceration and draining tracts with grains
Onychomycosis
Claw disease
How to diagnose dermatophytosis
Direct examination of hair/scales
Wood’s lamp
Fungal culture
Fungal PCR
Skin biopsy - if deep infections suspected
Direct examination of hair/scales
○ Gentle skin scrape/pluck hair from lesion margin
○ Select with Wood’s lamp if possible
○ Place in liquid paraffin on microscope slide, add coverslip
Infected hairs look distorted/paler/wider
Arthrospores seen around hair
+/- Hyphae within hair shaft
Wood’s Lamp
Microsporum spp. only
Will fluoresce
UV spectrum light
Fungal culture
McKenzie toothbrush technique
Can’t distinguish between carriage and disease
-ve if no growth after 14 days
Fungal PCR
Very sensitive
Faster than culture
Samples only from lesions
Can’t distinguish between carriage and disease
Malassezia Infection Pathogenesis
Malassezia is a fungi present in normal skin microbiome
Infections is caused by dysbiosis
Shift to more pathogenic strains
Almost ALWAYS a secondary infections
Not contagious
Clinical presentation of malassezia dermatitis in dogs
Erythema
Grease
Scale
Crust
Chronic changes (lichenification, hyperpigmentation)
Often malodourous
Focal/multifocal/generalised
Diffuse/well-demarcated
Erythro-ceruminous otitis
Commonly affected areas of malassezia dermatitis
Ears
Lips
Muzzle
Interdigital skin
Flexor surfaces/medial aspects of limbs
Ventral neck/body
Axillae
Perineum
Also paronychia (claw fold infection)
Clinical presentation of malassezia dermatitis in cats
○ Pruritus more variable
○ Otitis
○ Acne
○ Paronychia
○ Secondary to certain systemic diseases
