34 – Dermatophytes (ringworm)

Question 1

Microbiological characteristics

Answer 1

• Septate fungi
• Microsporum: boat shaped macroconidia
• Trichophyton: cigar shaped macroconidia
• Utilize keratin for growth
• Relatively slow growing
• Biocontainment level 2

Question 2

Answer 2

• Microsporum: boat shaped macroconidia

Question 3

Answer 3

• Trichophyton: cigar shaped macroconidia

Question 4

Natural host or habitat

Answer 4

• Can be described as geophilic or zoophilic
• Transmission depends on species
• Direct contact with infected hair, or contaminated environment
• Fleas from infected animals can serve as mechanical vectors
• *infectious dose is unknown (thought to be >100 spores)

Question 5

Geophilic

Answer 5

• Free living saprophytes in soil

Question 6

Zoophiles

Answer 6

• Adapted to survival in host skin

Question 7

Virulence factors:

Answer 7

1. Infective arthrospores germinate following adherence to keratinized structure
2. Trauma, moisture and maceration of skin facilitates infection
3. Keratin hydrolyzing ability allows invasion of skin, hair and feathers
4. Incubation period is 1-3 weeks
5. Host inflammatory response leads to lesions
   a. Round lesion: ‘ringworm’
   b. Alopecic
6. Clinical disease more common in warm humid climates

Question 8

Ringworm lesions in dogs (usually M. canis)

Answer 8

• Foci of alopecia
• Follicular papules
• Scales, crusts
• Lesions may have central area of pigmentation
• May have similar appearance as deep pyoderma
• *pruritus is VARIABLE
• *can be GENERALIZED (over large portions of body)

Question 9

Ringworm wide spectrum of clinical presentation in cats (usually M. canis)

Answer 9

• Mimic other dermatological conditions
• *Inapparent, silent infection
• Focal or multi-focal
• May or may not have scaling
• May or may not be pruritic
• Erythema and scaling of outer pinna=common presentations
• *granulomatous dermatitis is also possible (poor prognosis)

Question 10

Ringworm in kittens

Answer 10

• Erythema and scaling
  o Muzzle, ears, face, forelegs=most common sites

Question 11

Ringworm ‘treatment’ in dogs and cats

Answer 11

• Generally SELF-LIMITED INFECTION
• KEY=clip hair coat (prevent contamination of environment)
• Topical therapy possible
  o Whole body shampooing/dips most effective
• Systemic therapy: anti-fungals
• Decontaminate environment

Question 12

Decontaminating environment with dogs and cats with ringworm

Answer 12

• Can persist for long times
• Remove soft pet specific surfaces (beds, blankets, etc.)
• Purchase a new vacuum which can then be discarded
• Bleach disinfection of non-porous surfaces

Question 13

What is the most common species in horse ringworm?

Answer 13

• Trichophyton equinum
  o Infections typically superficially

Question 14

Where do lesions in horses with ringworm normally occur?

Answer 14

• Axilla or rump
• Then later spread to head and limbs

Question 15

Horse ringworm lesions

Answer 15

• Typically superficially
• 1. Begin as reddened, raised areas
• 2. After ~7 days hair falls out
• 3. Becomes scabby and crusty
• 4. Hair re-growth begins in 24-30 days

Question 16

What is the most common species of ringworm in cattle?

Answer 16

• Tichophyton verrucosum

Question 17

Cattle ringworm lesions

Answer 17

• Most commonly on head/neck
• Heavy grey crusts over lesions
• Alopecic spots develop
• NOT typically pruritic

Question 18

Ringworm is common in humans

Answer 18

• Presentation depends on site of infection
• Can occur at variety of body sites

Question 19

What are the risk factors for humans to get ringworm?

Answer 19

• Use of public showers
• Contact sports (ex. wrestling)
• Tight shoes
• Excessive sweating
• Some animal contact

Question 20

How to prevent ringworm in humans?

Answer 20

• Keep skin clean and dry
• Wear shoes that let your feed breath
• Don’t walk barefoot in public lockers or showers
• Don’t share towels
• Hand hygiene after playing with animals
• Shower immediately after sports
• Change socks and underwear daily

Question 21

Sample collection and handling

Answer 21

• PLUCK hair from lesions
• Scabs from edge of lesion
• Brushings
• Possible biopsies

Question 22

Why pluck hair from lesions?

Answer 22

• Fungi more likely at base in hair
• Preferentially pluck damaged looking hair

Question 23

How do you collecting brushings?

Answer 23

• Using a toothbrush
• Brush hair coat 2-3 minutes if unsure if/where exactly lesions are
• Gently brush lesions if visible

Question 24

Lab ID

Answer 24

• Woods lamp fluorescence (50% M. canis glows under UV)
• KOH wet mount of hairs, nails or scabs
  o Make fungal elements more apparent
• Fungal cultures: dermatophyte test media
• Histology

Question 25

Zoonotic/interspecies transmission

Answer 25

• Always consider it ZOONOTIC
• Children, elderly, transplant and cancer patients: at risk of more severe disease
• 50% of people in household with infected cats develop lesions
• Cats can carry T. rubrum (agent of athlete’s foot): transmission suspected
• *transmission b/w cats and agricultural animals

Question 26

Treatment options

Answer 26

• Most are self-limiting
• Different for the species

Question 27

Treatment options: dogs and cats

Answer 27

• 3 pronged approach
  o Environmental decontamination
  o Topical therapy (enilconazole)
  o Systemic therapy: azoles, terbinafine

Question 28

Treatment options: horses

Answer 28

• Shampoos

Question 29

Treatment options: cattle and small ruminants

Answer 29

• Enilconazole rinses