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Small Animal Medicine II > Dermatophytosis > Flashcards

Dermatophytosis Flashcards

1
Q

What are 3 classifications of cutaneous fungal infections?

A
  1. dermatophytosis - superficial
  2. intermediate - opportunistic
  3. systemic - cutaneous manifestations of systemic infection
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2
Q

What are 4 steps to the pathogenesis of dermatophytosis?

A
  1. invasion of non-viable, keratinized tissue
  2. production of metabolic byproducts and toxins cause inflammation and hypersensitivities
  3. secondary folliculitis/furunculosis
  4. severe infection develops in immunocompromised hosts (on glucocorticoids)
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3
Q

How do most dermatophytes infecting animals deposit their spores?

A

ectothrix - place spores around the hair shaft

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4
Q

What are 5 risk factors for developing dermatophytosis?

A
  1. age - young, old
  2. immune status
  3. exposure to critical masses of arthrospores
  4. cutaneous trauma or increased hydration
  5. genetics
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5
Q

What are 3 clinical features of dermatophytosis?

A
  1. circular alopecic areas of erythema, crusts, scales, hyperpigmentation, nodules, or pustules
  2. brittle or broken hairs
  3. mild to moderate pruritus (cats > dogs)
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6
Q

Dermatophytosis, dog:

A
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7
Q

Dermatophytosis, cat:

A

more pruritic compared to dogs, but not at the level of flea bite allergies or scabies

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8
Q

Dermatophytosis:

A

scale, broken hair (seems stubbly)

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9
Q

Which species of dermatophytes has a unique presentation?

A

Nannizzia gypseum –> elevated nodules with deeper infection

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10
Q

Dermatophytosis:

A
  • nodular
  • draining tract from hair follicle = furunculosis
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11
Q

Trichophyton mentagrophytes:

A
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12
Q

Dermatophytosis:

A

draining tract = furunculosis

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13
Q

Dermatophytosis:

A
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14
Q

What are the 3 most common dermatophytes of dogs and cats?

A
  1. Microsporum canis - transmission from animal-to-animal
  2. Nannizzia gypseum - found in soil
  3. Trichophyton mentagrophytes - wildlife
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15
Q

What 5 fungal contaminants can be found on samples that may look like dermatophytosis?

A
  1. Aspergillus
  2. Alternaria
  3. Penicillium
  4. Rhizopus
  5. Mucor
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16
Q

What are 5 diagnostics used for dermatophytosis?

A
  1. Wood’s lamp
  2. trichogram + KOH preparation
  3. fungal culture WITH microscopic ID
  4. fungal PCR
  5. skin biopsy
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17
Q

What is a Wood’s lamp? What species of dermatophyte particularly fluoresces?

A

UV light with nickel oxide filter

M. canis fluoresces 50% of the time, depending on light, darkness of the room, and how long the light was on the organism –> SCREENING ONLY, may be positive with topical meds

18
Q

What technique is most commonly used for trichogram preparations for diagnosing dermatophytosis?

A

mineral oil + KOH to dissolve hair/bubbles and observe hyphae and spores

  • positive is positive
  • negative is equivocal
19
Q

Trichogram, dermatophytosis:

A

spores on shaft, hyphae surrounding

20
Q

Trichogram, dermatophytosis:

A

spores on shaft, hyphae make it difficult to appreciate border of hair

21
Q

What is considered the gold standard for diagnosing dermatophytosis? What is considered proper technique? What is an essential part?

A

fungal culture

  • avoid over-inoculation, which can lead to overgrowth
  • incubate at 25-30 C
  • growth by 3-7 days

microscopic confirmation - do not rely on color change of DTM agar or point of care tests

22
Q

Dermatophytes, DTM:

A

color change indicative of infection

  • do NOT rely on this, perform a microscopic examination
  • some saprophytes may be able to induce a color change
23
Q

What are the most common dermatophyte isolates?

A
  • Microsporum canis
  • Microsporum gypseum
  • Trichophyton mentagrophytes
24
Q

What are the most common saprophyte isolates?

A
  • Alternaria
  • Mucor
  • Penicillium
  • Aspergillus
  • Rhizopus
25
Q

What samples are required for fungal PCRs when diagnosing dermatophytosis? How is this test best interpreted?

A

10-20 hairs plucked and scraped from active borders of the lesion, aspirated purulent material, and claws

in combination with Wood’s lamp examination, hair examination, and culture/ID

26
Q

What is most commonly seen on biopsy/histopathology in cases of dermatophytosis?

A
  • folliculitis/furunculosis
  • organisms seen with PAS, silver, or Giemsa stains

poor sensitivity, high specificity

27
Q

What are the 2 objectives when treating dermatophytosis?

A
  1. shorten course of infection and reduce severity of lesions/discomfort
  2. reduce dissemination of infective materials (hair, scale) into the environment

decontaminate/treat pet and environment = reduced zoonotic risk

28
Q

What are the 2 purposes of total body clips in cases of dermatophytosis? What may occur?

A
  1. reduce infectivity (contagion)
  2. speeds recovery

environmental contamination –> avoid trauma, disinfect instruments

29
Q

What are the 2 methods of topical therapy in treating dermatophytosis?

A
  1. ADJUNCTIVE - lotions and cream for focal lesions, daily or EOD, work medication inward to reduce spread
  2. CONCURRENT - bathe pet weekly with Miconazole, Chlorhexidine, or Ketoconazole shampoos

NOT recommended as sole treatment

30
Q

What topicals can be used as the sole treatment of dermatophytosis?

A
  • Enilconazole rinse
  • Lime sulfur bath
  • Miconazole-Chlorhexidine baths

twice weekly

31
Q

What are 4 systemic therapy options for cases of dermatophytosis?

A
  1. Griseofulvin (4-8 weeks)
  2. Azoles - Ketoconazole, Itraconazole, Fluconazole (4-8 weeks) –> fungistatic
  3. Lufenuron
  4. Terbinafine
32
Q

What side effects are associated with Griseofulvin?

A
  • anorexia
  • GI disturbances - diarrhea
  • teratogenesis
  • bone marrow suppression - FIV+ cats
33
Q

What is the mechanism of action of azoles?

A

inhibit lanosterol-14alpha-demethylase (CYP-450) responsible for forming ergosterol

34
Q

What are 2 pharmacological characteristics to the mechanism of Ketoconazole? When is this medication best given?

A
  1. highly protein-bound - penetrates poorly into CNS, eyes, and prostate
  2. inhibits p-glycoprotein pump in GIT, liver, and brain

with a meal to increase absorption

35
Q

What side effects are associated with Ketoconazole use?

A
  • anorexia (cats)
  • diarrhea
  • increased hepatic enzyme concentrates
  • alopecia
36
Q

Which azole is considered the best for treating dermatophytosis? What side effects are associated?

A

Itraconazole for dogs AND cats–> $$, better absorption into skin

  • increased hepatic enzyme concentrations
  • vomiting
  • anorexia
  • AVOIDED in pregnant animals
37
Q

How does Fluconazole compare to the other azoles? What adverse effects are associated?

A

excellent penetration into CSF, eyes, and claws

  • increased hepatic enzymes
  • AVOIDED in pregnant animals
38
Q

How does Terbinafine compare to the other systemic antifungals used for treating dermatophytosis?

A
  • FUNGICIDAL - inhibits squalene epoxidase necessary for ergosterol synthesis
  • relatively few side effects - elevated ALT
39
Q

What are 5 recommendations for environmental decontamination in cases of dermatophytosis?

A
  1. launder bedding, carpet, etc.
  2. change furnace filters and heating ducts
  3. vacuum and dispose
  4. disinfectant sprays/cleansers - 1:10 bleach in non-porous surfaces
  5. foggers/smokers - Enilconazole in large, open areas
40
Q

What is a major consideration during the treatment of dermatophytosis?

A

it is contagious, infectious, and zoonotic

  • human infection is COMMON
  • lesions can be painful
  • therapy can be expensive and long
41
Q

What risk factors in humans are associated with dermatophytosis?

A
  • adoption from human societies and shelters
  • exposure to large number of animals - groomers, veterinarians, shelter workers
  • immunosuppression
42
Q

Overall, what are the systemic treatments of choice for dermatophytosis?

A
  • Terbinafine - fungicidal
  • Itraconazole

systemic treatment recommended with multiple lesions

Small Animal Medicine II (57 decks)

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