Dermatophytosis in Domestic Animals (Santoro)

Question 1

Dermatophytes

Answer 1

“Ringworm”. Fungi that infect keratinized tissues (skin, hair, claws/hooves, feathers, quills)

Question 2

Dermatophyte species affecting the dog & cat

Answer 2

• Microsporum canis (reservoir: cats)
• Microsporum gypseum (reservoir: soil)
• Trichophyton mentagrophytes (reservoir: rodents, rabbits, pocket pets)
• Microsporum persicolor

Question 3

Predisposing factors for dermatophytosis

Answer 3

• Decr. grooming
• Microtrauma
• Excessive hydration/maceration
• Warm, humid
• Lack of sun exposure
• Strong cell-mediated immunity

Question 4

Predilections for dermatophytosis

Answer 4

• White Persians and Himalayans
• Terriers
• Young animals
• Sick & emaciated animals

Question 5

Clinical signs of dermatophytosis in dogs & cats

Answer 5

• Cutaneous signs
  
  • extremely variable
  • absent to moderate pruritis
  • erythema/alopecia
  • crusting/scaling/pustules
  • miliary dermatitis (cats)
  • dermal nodules/plaques
  • muzzle & feet most affected

Question 6

Clinical signs of dermatophytosis in horses

Answer 6

• Follicular pustules
• Variable-sized annular alopecic areas
• Severe scaling, crusing, pustules, ulcers, pruritis
• Saddle & tack regions
• Urticaria-like lesions

Question 7

Clinical signs of dermatophytosis in cattle

Answer 7

• Circular, alopecic areas
• Severe scaling, crusting, suppuration
• Pain and pruritis​ - variable

Question 8

Kerion

Answer 8

Well-circumscribed nodular mass

Question 9

Dermatophytosis diagnosis

Answer 9

• Hx & physical exam
• Wood’s lamp (black light)
• Trichogram (hair pluck)
• Fungal culture (ID macroconidia)
• Skin biopsy/histopath

Question 10

MacKenzie technique

Answer 10

• Useful for feline asymptomatic carriers of dermatophytosis
• Use hairs collected from brush or cut brush bristles and place them on the media

Question 11

Slide preperation

Answer 11

Use clear scotch tape to dab colony w/ sticky side. Place tape onto slide that already has a drop of stain on it.

Question 12

Principles for treatment of dermatophytosis

Answer 12

• Elimination of infection from host
• Prevention of further dissemination of infective spores
• Removal of infective spores already in environment

Question 13

Treatment of dermatophytes

Answer 13

• Healthy animals can self-cure in 12-17 wks if infective spores are removed from the environement
• Systemic, topical, and environmental therapy
• Treat all animals in contact

Question 14

Topical therapies for dermatophytosis

Answer 14

• Ketoconazole
• Miconazole
• Chlorohexidine
• Lime sulfur
• Clipping hair controversial
  
  • Removes contaminated hair
  • Creates microlesions

Question 15

Systemic therapies for dermatophytosis

Answer 15

• Ketoconazole
• Itraconazole
• Fluconazole
• Terbinafine
• Griseofulvin

Question 16

Griseofulvin (general info)

Answer 16

• Fungistatic
• Variable oral absorption
  
  • Incr. fatty meal
• Only effective against dermatophytes

Question 17

Griseofulvin side effects

Answer 17

• Vomiting
• Diarrhea
• Anorexia
• Bone marrow suppression
• Siamese, himalayans, abyssinians
• Monitor CBC, FIV, FeLV and other viruses
• Teratogenic

Question 18

Ketoconazole (general info)

Answer 18

• Fungistatic
• Good oral absorption
  
  • Incr. fatty meal
  • Decr. non-acid gastric environment

Question 19

Ketoconazole side effects

Answer 19

• Vomiting
• Diarrhea
• Anorexia
• Interfere w/ steroid synthesis
• Inhibit cytochrome P450
• Better tolerated in dogs than cats
• Contraindicated in pregnant animals

Question 20

Itraconazole (general info)

Answer 20

• Fungistatic (low) - fungicidal (high)
• Preferred for feline fungal infections
• Good oral absorption
  
  • Incr. fatty meal

Question 21

Itraconazole side effects

Answer 21

• Uncommon
• GI upset (rare)
• Hepatotoxicity (rare)
• Reversible, dose-dependent cutaneous vasculitis in dogs at higher doses
• Mild inhibition of cytochrome P450
• Not recommended in pregnant animals (teratogenicity, embriotoxicity)

Question 22

Fluconazole

Answer 22

• Fungistatic
• Broad antimycotic spectrum
• Side effects uncommon (GI upset)
• Mild inhibition of cytochrome P450
• Recommended for patients w/ hepatic dz

Question 23

Terbinafine

Answer 23

• Fungicidal
• Residual effect (accumulates in keratinized tissue)
• Vomiting & facial pruritis in cats
• Incr. liver enzymes
• NO inhibition of cytochrome P450

Question 24

Immunotherapy for dermatophytosis

Answer 24

• Killed M. canis vax
  
  • licensed for prevention and treatment of lesions, but not the dz
  • causes slightly decr. severity of initial infection
• Cattle
  
  • success in prophylactic or therapeutic use

Question 25

Environmental decontamination of dermatophytosis

Answer 25

• Swiffer/vacuum
• Detergent
• Bleach (1:10)
• Enilconazole
• Lime sulfur

Question 26

Duration of dermatophytosis therapy

Answer 26

• No growth on 2 sequential weekly cultures
• 2 negative cultures one month apart

Question 27

Onychomycosis

Answer 27

• Fungal infection of nail
• Prognosis for cure is guarded, will take several months (6-12+) if at all
• Itraconazole and terbinafine
• Onychectomy (declaw) may be indicated

Question 28

Large animal dermatophytosis therapy

Answer 28

• Infections usually self-limiting
• Topical (lime sulfur spray)
• Treat 2 wks past clinical cure
• Isolation
• Environmental decontamination
• Decr. crowding, incr. UV light exposure