Dermatophytes

Question 1

Dermatophytes

Answer 1

-septate fungi
-use keratin to grow
-relatively slow growing
-biocontainment level 2

Question 2

Microsporum vs Trichophyton

Answer 2

Microsporum- boat shaped macroconidia
3-5days growth

Trichophyton- cigar shaped macroconidia
7-14 days growth

Question 3

Appearance of microsporum canis

Answer 3

-boat shaped

Question 4

Appearance of Trichophyton

Answer 4

-cigar shaped macroconidia

Question 5

Host and habitat

Answer 5

1. geophilic- free living saprophytes in soil
   eg. M. gypsum
2. zoophilic- adapted to survival in host skin
   eg. microsporum canis (cats), Trichophyton verrucosum (cattle)

Question 6

Transmission of dermatophytes

Answer 6

-depends on species (animal to animal, animal to human, human to human)

-from direct contact with infected hair or contaminated environment

-fleas as mechanical vectors

Question 7

Infectious doses

Answer 7

unknown
-but thought to be more than 100 spores

Question 8

Virulence Steps

Answer 8

1. Infective arthrospores germinate following adherence to keratinized structures
2. trauma, moisture, maceration of skin facilitated infection
3. Keratin hydrolyzing ability allows invasion of skin, hair, feathers
4. incubation period is 1-3weeks
5. Host inflammation= lesions (ring worm and alopecic)
6. clinical disease more common in warm humid climates

Question 9

Species affecting dogs

Answer 9

-M canis
T. netagrophytes
T. gypsum

Question 10

Species affecting cats

Answer 10

M canis (90% of infections)

Question 11

Species affecting horses

Answer 11

T. equinum

Question 12

Species affecting cattle

Answer 12

T. verrucosum

Question 13

Species affecting pigs

Answer 13

M nanu

T. mentagrophytes

Question 14

Clinical signs of ringworm in dogs

Answer 14

-foci or alopecia
-follicular papules
-scales, crusts
-lesions may have central area of pigmentation
-may be similar to deep pyoderma
-pruritus variable

**lesions can be generalized over large portions of body and if so are likely linked to underlying disease

Question 15

Clinical signs of ringworm in cats

Answer 15

-mimic other dermatological conditions
-inapparent silent infection
-focal or multi focal
-sometimes scaling
-sometimes pruritic
-erythema and scaling of outer pinna (COMMON)

-granulomatous dermatitis also possible= ulcerated nodules; generalized infectoins
Poor prognosis

Question 16

Specific signs of ringworm in kittens

Answer 16

-erythema and scaling on muzzle, ears, face, forelegs

Question 17

Treatment for ringworm in dogs and cats

Answer 17

-generally self limiting
-clip hair to prevent additional contamination to environment
-topical therapy (shampoos, dips)
-systemic therapy
-clean environment (remove soft bedding, new vaccuum, bleach)

Question 18

Ringworm in horses

Answer 18

-commonly caused by Trichophyton equinum

-typically on axilla or rump, and then to head and limbs
-red raised areas
-hair falls out after 7 days
-scabby and crusty
-hair regrows 24-30days

Question 19

Ringworm in cattle

Answer 19

-usually caused by Trichophyton verrucosum

-lesions on head/neck
-heavy grey crusts over lesions
-alopecic spots
-not typically pruritic

Question 20

Ringworm in people

Answer 20

-presentation depends on site of infection; can occur at a variety of body sites

Risk factors: public showers, contact sports, tight shoes, excessive sweating, animal contact

Question 21

control of ringworm in people

Answer 21

-keep skin dry and clean
-wear shoes that let your feet dry
-dont share towels
-dont walk barefoot
-hand hygiene after animals
-shower after sports
-change socks and underwear daily

Question 22

Sample collection and handling

Answer 22

1. pluck hair from lesions (fungi likely at base of hair; use damaged looking hair)
2. scabs from edge of lesion
3. brushings (brush hair with toothbrush)
4. biopsies

Question 23

Lab ID

Answer 23

-Woods lamp fluorescence (only 50% will fluoresce so not guaranteed)

-KOH wet mounts of hairs, nails, scabs
*base degrades host tissues making fungus more apparent

-Fungal cultures- Dermatophyte test media

-Histology

Question 24

Zoonoses

Answer 24

-Ringworm always considered zoonotic
-children, elderly, transplant and cancer patients are more at risk
-50% of people in cat households develop lesions
-cats can carry T. rubrum (athletes foot)
-Transmission: cats and agricultural animals

Question 25

Treatment options

Answer 25

-usually self limiting

-Dogs/Cats: environmental decontamination, topical therapy enilconazole), systemic therapy (azoles, terbinafine, griseofulvin)

-horses: shampoos

-cattle and small ruminants: enliconazole rinses