Dermatophytosis in domestic animals

Question 1

1. most imp dermatophyte spec in dogs and cats
2. recog host factors leading to dermatophytosis in dogs/cats
3. recognize broad spec clinical presentations, understand why this is overdiagnosed
4. 3 major diagnostic techniques, appreciate accuracy
5. proper collection of specimens and proper use and principles underlying DTM
6. list basic principles of treatment and management of dermatophytosis in small animals
7. choose the most useful treatment options and their side effects for dermatophytosis in small animals

Question 2

Most commonly isolated dermatophytes in domestic animals

Answer 2

1. Microsporum
2. Trichophyton

Question 3

Anamorphs

Answer 3

1. M. Canis
2. M. gypseum
3. M. persicolor
4. M. nanum
5. T. mentagrophytes

Question 4

Teleomorphs

Answer 4

1. Arthroderma otae
2. A. gypseum or A. incurvatum
3. A. persicolor
4. A. obtusum
5. A. vanbreuseghemii or A. benhamiae

Question 5

Geophilic dermatophytes

Answer 5

• normally inhabit soil
• decompose keratinous debris

Question 6

Anthropophilic dermatophytes

Answer 6

• preference for human tissue

Question 7

Zoophilic dermatophytes

Answer 7

• preference for animal tissue

Question 8

Clinical incidence of dermatophytosis

Answer 8

• true incidence unknown ( ~ 2% all skin infections in animals)
• 4-100% cats may act as fomites
• dermatophytosis mimics
  
  1. pyoderma
  2. allergic dermatitis
  3. parasitic dermatitis

Question 9

generalities of incidence of dermatophytosis

Answer 9

1. infections more common in warm, humid tropical geographic areas
2. infections more common when animals house in poor sanitary conditions or overcrowded
3. outbreaks in cattle may occur during fall and winter from close confinement

Question 10

Pathophysiology

Answer 10

• Transmission: direct contact, or airborn transmission, zoonotic and reverse
• Contaminated brushes, clippers, tack, furniture, etc…
• Long-haired and non-grooming animals may be more susceptible
• M. Canis spores may remian in env up to 18 mo
• Infective spores can adhere to keratinocytes, but not healthy intact skin
• Fungal hyphae grow downward on surface of anagen hairs
• Development of strong cell-mediated immune response for recovery/immunity

Question 11

Clinical signs of dermatophytosis

Answer 11

• follicular damage and subsequent inflammation
• marked to little inflammation
• Erythema and follicular papules and pustules secondary to epidermal and follicular inflammation
• Typical ring of alopecia with possible healing in the middle

Question 12

Kerion reactions

Answer 12

• more common with geophilic or other fungals species poorly adapted to host

Question 13

onychomycosis

Answer 13

• invasion of keratin and infection of the claw
• rare and may produce refractory or recurrent disease
• may lead to chronic nail fragility and deformity
• may be accompanied by
  
  • pododermatitis: severe inflammation of interdigital spaces
  • paronychia: severe inflammation of claw fold regions

Question 14

M. Canis and cats

Answer 14

• responsible for > 90% of feline infections
• endemic in catteries
• important zoonotic organisms
• Dermatiophytic pseudomycetomas subcutaneous nodules from inflammatory reaction to fungal hyphae w/in dermis

Question 15

M. Canis and dogs

Answer 15

• causes 70-80% of infections
• dermatophytes should be a differential for any papular, pustular dermatosis or comedones

Question 16

Diagnosis of dermatophytes

Answer 16

• Woods lamp examination: ultraviolet light
  
  • carrier cats not positive
  • M. canis only dermatophyte of veterinary imp that may produce fluorescence
  • should confirm with culture
• Direct exam of hairs and scale
  
  • not sensitive but can be specific
• Fungal culture
  
  • Only reliable method for diagnosing and identifying causative agent of dermatophyte infection