Fungal Causes of Skin Disease

Question 1

Types of fungi which cause skin disease

Answer 1

Commensals
* Malassezia
Transient contaminants
* Environmental saprophytes
* Sometimes dermatophytes
Active pathogens
* Dermatophytes

Question 2

How do fungi cause skin disease?

Answer 2

Mycoses
Superficial
Deep
Systemic
Hypersensitivity

Question 3

Dermatophytosis

Answer 3

‘Ringworm’
Caused by dermatophytic fungi
* Trichophyton spp.
* Microsporum spp.

Contagious
Zoonotic!

Question 4

Geophilic

Answer 4

Adapted for environment

Question 5

Zoophilic

Answer 5

Adapted for mammals
Most common source of animals disease

Question 6

Anthropophilic

Answer 6

Adapted for man

Question 7

Stages of dermatophytosis infections

Answer 7

1. Skin microtrauma and moisture
2. Inoculation and germination of infective arthrospores
3. Germ tubes penetrate start corneum
4. Growth of fungal hyphae
5. Lesions within 5-7 days

Question 8

What species is dermatophytosis common in?

Answer 8

Cow
Horse
Cat
Sometimes dog
Zoonotic to humans

Question 9

Clinical signs of dermatophytosis

Answer 9

Alopecia
Folliculitis
Patchy, multifocal, well-demarcated circular grey lesions
Scale and crust
Variable pruritus
Affects haired skin

Question 10

Uncommon presentation of dermatophytosis

Answer 10

Furunculosis
Fungal Kerion
Pseudomycetoma
Onychomycosis

Question 11

Furunculosis

Answer 11

Deep infection of hair follicle
Rupture of follicle wall
Accumulation of purulent material and necrotic tissue

Looks similar to deep pyoderma

Question 12

Fungal Kerion

Answer 12

○ Nodular inflammatory mass due to inoculation of fungus into dermis
○ Especially hunting/working dogs

Question 13

Pseudomycetoma

Answer 13

○ Subcutaneous/deep mycosis
○ Nodular granulomas
○ +/- ulceration and draining tracts with grains

Question 14

Onychomycosis

Answer 14

Claw disease

Question 15

How to diagnose dermatophytosis

Answer 15

Direct examination of hair/scales
Wood’s lamp
Fungal culture
Fungal PCR
Skin biopsy - if deep infections suspected

Question 16

Direct examination of hair/scales

Answer 16

○ 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

Question 17

Wood’s Lamp

Answer 17

Microsporum spp. only
Will fluoresce
UV spectrum light

Question 18

Fungal culture

Answer 18

McKenzie toothbrush technique
Can’t distinguish between carriage and disease
-ve if no growth after 14 days

Question 19

Fungal PCR

Answer 19

Very sensitive
Faster than culture
Samples only from lesions
Can’t distinguish between carriage and disease

Question 20

Malassezia Infection Pathogenesis

Answer 20

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

Question 21

Clinical presentation of malassezia dermatitis in dogs

Answer 21

Erythema
Grease
Scale
Crust
Chronic changes (lichenification, hyperpigmentation)
Often malodourous
Focal/multifocal/generalised
Diffuse/well-demarcated
Erythro-ceruminous otitis

Question 22

Commonly affected areas of malassezia dermatitis

Answer 22

Ears
Lips
Muzzle
Interdigital skin
Flexor surfaces/medial aspects of limbs
Ventral neck/body
Axillae
Perineum
Also paronychia (claw fold infection)

Question 23

Clinical presentation of malassezia dermatitis in cats

Answer 23

○ Pruritus more variable
○ Otitis
○ Acne
○ Paronychia
○ Secondary to certain systemic diseases