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Dermatophytosis Flashcards

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1
Q

What is dermatophytosis? Is it a parasite?

A
  • Cutaneous fungal infection

- NO

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2
Q

Where do dermatophyte invade?

A
  • Keratinized structures

- e.g. hair, horns, nails, feathers, cornified epithelium

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3
Q

What should happen with dermatophytosis in healthy animals?

A
  • It should resolve on its own

- This depends on the immune status of the host

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4
Q

Is dermatophytosis zoonotic?

A
  • YES
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5
Q

What are the three classifications of dermatophytosis?

A
  • Zoophilic
  • Geophilic
  • Anthropophilic
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6
Q

Meaning of zoophilic

A
  • Primarily infect animals vs man BUT can be zoonotic
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7
Q

Zoophilic ringworm

A
  • Microsporum canis
  • Trichophyton equinum
  • T. mentagrophytes
  • T. verrucosum
  • M. nanum
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8
Q

Geophilic meaning

A
  • Inhabits soil

- Decompose keratinaceus organic debris

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9
Q

Examples of geophilic fungi

A
  • M. gypseum
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10
Q

Which categories of dermatophyte do veterinarians deal with?

A
  • Geophilic and zoophilic primarily
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11
Q

Anthropophilic meaning

A
  • Primarily infect man and rarely animals
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12
Q

WHat is an arthrospore?

A
  • Infective portion of the organism that causes infection
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13
Q

How does the arthrospore form?

A
  • Forms by segmentation and fragmentation of hyphae
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14
Q

Where does the arthrospore adhere?

A
  • Keratin!
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15
Q

What are the two types of infection for dermatophytosis?

A
  • Ectothrix

- Endothrix

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16
Q

Ectothrix definition

A
  • Infection produced outside the hair shaft
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17
Q

Endothrix definition

A
  • Produced inside the hair shift
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18
Q

Which type of infection is primarily anthropophilic?

A
  • Endothrix
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19
Q

Clinical incidence of dermatophytosis in dogs vs cats

A
  • Common in cats

- Uncommon in dogs

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20
Q

Which genera are responsible for 99% of clinical cases?

A
  • Microsporum and Trichophyton
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21
Q

Which regions have dermatophytosis most commonly?

A
  • Warm, humid, tropical areas
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22
Q

Conditions where dermatophytosis flourishes?

A
  • Poor housing conditions (puppy mills, catteries, pet shops, shelters)
  • Warm, humid tropical areas
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23
Q

What can increase likelihood that a dog has a dermatophytosis infection?

A
  • Infected cat exposure
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24
Q

Risk factors for dermatophytosis

A
  • Young animals

- Immune suppression

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25
Q

Transmission of dermatophytosis

A
  • Direct cnontact with infected host, fomite, or contaminated environment
  • Animal to man and man to animal transmission is possible
  • Airborne transmission is believed to occur
  • Ectoparasites (fleas, cheyletiella) especially in catteries and multiple animal households
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26
Q

Reservoirs of infection for dermatophytosis

A
  • Cats and rodents

- Asymptomatic carriers

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27
Q

What structures of the epidermis must the dermatophyte invade?

A
  • Keratin of stratum corneum and/or hair
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28
Q

What type of hair does dermatophytosis prefer?

A
  • Anagen hairs (growth phase)

- Growing hairs contain carbohydrates, nitrogenous substances, and nucleoprotein derivatives in addition to keratin

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29
Q

Physical barriers to infection

A
  • Hair

- Stratum corneum

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30
Q

Pathophysiology of dermatophytosis

A
  1. Invades keratin of stratum corneum and/or hair
  2. Only grows in anagen (growing) hairs
  3. Fungi grow downward to just above the hair bulb
  4. The hair shaft is weakened and breaks
  5. Induces hair to enter telogen, and the infection resolves in that hair. By this time, it has spread to a neighboring hair.
  6. Inflammation expels fungus from the hair and infection spreads peripherally
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31
Q

Incubation for dermatophytosis

A

4-30 days

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32
Q

What determines the clinical signs associated with dermatophytosis?

A
  • The host’s response to fungus
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33
Q

Well adapted species of dermatophyte

A
  • M. canis
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34
Q

Less well adapted species of dermatophyte

A
  • M. gypseum, T. mentagrophytes
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35
Q

Clinical signs with well adapted species of dermatophyte in cats vs dogs vs humans

A
  • Minimal inflammation with alopecia in cats

- More marked inflammation (e.g. ring like lesion) in dogs and humans

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36
Q

Clinical signs with less well adapted species of dermatophyte in cats vs dogs vs humans

A
  • More marked inflammation with alopecia in dogs, cats, and humans
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37
Q

What immunologic factors are at play with dermatophytosis?

A
  • Young vs old individuals
  • Serum and sebum are fungistatic
  • CMI is most important
  • No correlation between circulating antibodies and protection
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38
Q

What type of immunity is most protective with dermatophytosis?

A
  • Cell-mediated immunity
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39
Q

What is the classic lesion of canine dermatophytosis?

A
  • Circular patch of alopecia characterized by broken stubby hair, scaling, and mild erythema
  • Appears to be spreading outward, often with central healing
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40
Q

Clinical signs of canine dermatophytosis

A
  • Often quite variable

- Can be focal, multifocal, or generalized

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41
Q

What should you look for with generalized dermatophytosis?

A
  • Look for underlying immune suppression
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42
Q

Lesions possible with dermatophytosis

A
  • Papules
  • Pustules
  • Vesicles
  • These are increased degrees of inflammation
  • Classic lesion is circular patch of alopecia characterized by broken stubby hair, scaling, and mild erythema
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43
Q

Major differentials for dermatophytosis

A
  • Pyoderma

- Demodicosis

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44
Q

Dermatophytosis - normally pruritic?

A
  • Not usually
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45
Q

What are two other clinical presentations possible with dermatophytosis?

A
  • Kerions

- Onychomycosis

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46
Q

What is a kerion?

A

Nodular dermal reaction with ulceration and draining tracts caused by a fungi

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47
Q

Which species of fungi usually cause kerions?

A
  • M. gypseum or Trichophyton sp.

- Often from putting their nose in a hole

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48
Q

What is the pathophysiology of fungal kerions?

A
  • Extreme inflammatory reaction or hypersensitivity to dermal location of fungus
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49
Q

Locations of fungal kerions?

A
  • Face/muzzle/legs
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50
Q

Differentials for fungal kerion

A
  • Histiocytoma
  • Deep pyoderma
  • Neoplasia
  • Demodicosis
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51
Q

What is onychomycosis?

A
  • Infection of keratin at the nailbed
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52
Q

Clinical signs of onychomycosis?

A
  • Abnormal nail growth and brittle nails
  • Usually asymmetric
  • Usually skin is affected too
53
Q

Species that causes onychomycosis?

A
  • T. mentagrophytes
54
Q

How common is onychomycosis?

A
  • Pretty uncommon to rare
55
Q

How long is treatment for onychomycosis in general?

A
  • 9-12 months
56
Q

What is the most common species for feline dermatophytosis?

A
  • Microsporum canis (>95%)
57
Q

Feline dermatophytosis - where can it become endemic?

A
  • Catteries and shelters
58
Q

What are Dr. Mel’s rules for feline dermatophytosis?

A
  • All long-haired cats have dermatophytosis until proven otherwise
  • All cats SHOULD be checked for dermatophytosis before being adopted into a household
59
Q

Clinical signs for dermatophytosis in cats

A
  • Patches of alopecia, crusting, scaling, especially face and ears
  • Miliary dermatitis (erythematous crusts throughout the coat)
  • Asymptomatic carriers (in infected catteries, only kittens may be clinically affected)
  • Comedomes, symmetrical alopecia, ear margin alopecia, hyperpigmentation, paronychia
  • Nodules, kerions
60
Q

Is dermatophytosis usually pruritic in cats?

A
  • No
61
Q

What should you think with generalized form of dermatophytosis?

A
  • Think FeLV/FIV and ruling that out
62
Q

4 Reasons to treat dermatophytosis in cats even though it can spontaneously resolve?

A
  1. Zoonotic disease
  2. Decrease spread to other animals
  3. Decrease environmental contamination
  4. Speed recovery from infection
63
Q

Treatment for a single lesion/kerion (IN DOGS ONLY)

A
  1. Spot tx with topical antifungal creams
  2. Apply 1-2 times a day
  3. DO NOT USE COMBO STEROID PRODUCTS
  4. WHole-body treatment with topical dip can be helpful to treat subclinical areas
64
Q

Examples of antifungals for topical treatment in dogs?

A
  • Miconazole, clotrimazole, terbinafine
65
Q

Can you spot treat cats?

A
  • NO, never do it
66
Q

Treatment for multifiocal to generalized lesions

A
  1. Consider clipping hair coat (debatable but do it in long-haired cats)
  2. Treat entire body 2 times per week
  3. May need systemic treatment
  4. He typically combines entire body treatment with systemic treatment
  5. Long haired cats cannot usually be cured with topical therapy alone
67
Q

Examples of dips that can be used for multifocal to generalized dermatophytosis? Which is best?

A
  • Lime sulfur***
  • Enilconazole
  • Ketoconazole or miconazole containing shampoos
68
Q

What is Dr. Mel’s treatment for all animals with multifocal to generalized dermatophytosis and ESPECIALLY CATS?

A

Topical treatment with systemic treatment

69
Q

Features of rinses

A
  • Treat entire surface area
  • Minimizes rubbing of skin
  • Treatment can dry on the skin
70
Q

Why shouldn’t you use shampoos for treating dermatophytosis?

A
  • Little residual activity
  • Washing and rinsing could macerate skin
  • Spread of spores increased
71
Q

Frequency of:

  1. Lime sulfur dip
  2. Enilconazole
  3. Miconazole shampoos
A
  • Twice weekly
72
Q

Lime sulfur dip characteristics

A
  • Rotten eggs
  • Effective topical
  • Fungicidal on contact
  • Safe in newborn kittens and puppies
  • Non-toxic
  • Let “room air” dry
  • E-collar
73
Q

Enilconazole - who licensed for?

A
  • Dogs and horses

- Effective for cats

74
Q

Side effects of enilconazole

A
  • GI
  • Hypersalivation
  • Muscle weakness
  • Mildly elevated ALT
  • Death (Anecdotal)
  • Use e-collar!
75
Q

Miconazole shampoos

A
  • Synergism with chlorhexidine

- Can also be an effective treatment

76
Q

Systemic treatments - who gets?

A
  • Multi-focal to generalized lesions
  • Cats
  • Cases of immune-suppression
77
Q

How long to treat for dermatophytosis systemically?

A
  • Treat until you have BOTH a clinical cure and mycological cure
  • Can take a minimum of 6 weeks
78
Q

Which happens first: clinical or mycological cure?

A
  • Clinical cure happens first
79
Q

What is a mycological cure?

A
  • 2 consecutive negtive fungal cultures, 1 week apart

- OR negative PCR

80
Q

What do our antifungal treatments tend to target?

A
  • Ergosterol and squalene
81
Q

MOA of azoles

A
  • Diffuse through cell membrane of fungal organism
  • Block 14-alpha-demethylase
  • Blocking ergosterol synthesis, which is required for cell walls
  • Toxic sterols in the cell membrane
82
Q

Azoles - what important enzyme do they impact?

A
  • Affect mammalian cytochrome p450 and can lead to increased to decreased concentrations of other drugs
83
Q

Itraconazole - good or bad treatment for dermatophytosis?

A
  • Excellent
84
Q

Where does itraconazole accumulate?

A
  • Adipose tissue and sebaceous glands
85
Q

Itraconazole compounding

A
  • Avoid
86
Q

Accepted itraconazole protocol in cats

A
  • 5mg/kg PO alternating weeks
87
Q

Terbinafine - good or bad treatment for dermatophytosis?

A
  • Excellent
88
Q

Price of terbinafine?

A
  • Quite inexpensive
89
Q

Terbinafine MOA

A
  • Inhibits squalene epoxidase and disrupts fungal cell membrane
  • Squalene is a precursor for ergosterol
90
Q

Does terbinafine impact cytochrome p450?

A
  • NO
91
Q

Where does terbinafine store?

A
  • Adipose tissue
92
Q

Side effects of terbinafine?

A
  • Increases in ALT, ALP, and GI upset
93
Q

Fluconazole - is it a good treatment or not for dermatophytosis?

A
  • Said to have poor efficacy against dermatophytosis in the literature but more recent studies and anecdotally is believed to be an effective treatment
  • I don’t think he really recommends it
94
Q

Side effects of fluconazole compared to others

A
  • Overall better side effect profile than azoles and terbinafine
95
Q

Fluconazole MOA?

A
  • Inhibits ergosterol and disrupts fungal cell membrane
96
Q

Is absorption of fluconazole impacted by antacids?

A
  • No
97
Q

Is ketoconazole an effective treatment for dermatophytosis?

A
  • No
98
Q

Where does ketoconazole accumulate?

A
  • Adipose tissue
99
Q

Administration instructions for ketoconazole?

A
  • Dissolved by gastric aciditiy and should be given on an empty stomach
100
Q

Ketoconazole side effects

A
  • Interferes with endogenous cortisol synthesis in dogs and humans
  • Higher risk for side effects
101
Q

Where is ketoconazole metabolized?

A
  • Liver by cytochrome p450
102
Q

Ketoconazole MOA

A
  • inhibits ergosterol and disrupts fungal cell membrane
103
Q

Is griseofulvin recommended or not and why?

A
  • No

- Teratogenic, panelukopenia in cats, GI upset, ataxia

104
Q

Is lufeneron recommended or not and why?

A
  • Chitin synthesis inhibitor

- Ineffective as a treatment and preventative

105
Q

Are antifungal vaccines recommended or not and why?

A
  • No - do not protect
106
Q

Why is environmental control important for dermatophytosis?

A
  • Environment is a source of infection and may be the reason for reinfection
107
Q

How do you effectively control environmental spread of dermatophytosis?

A
  • THoroughly wash, dust, vacuum, scrub, and disinfect all surfaces, drapes, and other objects
  • Steam cleaning doesn’t kill unless bleach is added (1 oz per gallon with 10 minutes of contact time)
  • Wash beds and blankets with hot water and bleach
  • Enilconazole is effective environmental spray (use every 2 weeks)
  • Change heating and airconditioning filters
  • Clean vents
  • Quarantine for at least 15 days during initial treatment phases of systemic therpay and whole body treatment
108
Q

Treatment of dermatophytosis in multiple cat households/catteries?

A
  • Fungal culture or PCR ALL cats or assume they are all positive
  • Isolate and segregate infected and uninfected cats
  • Treat all positive cats
109
Q

What type of test is Wood’s lamp?

A
  • Initial screening light
110
Q

What is a Wood’s lamp?

A
  • UV light filtered through cobalt or nickel filter
111
Q

Which species will fluoresce under Wood’s lamp?

A
  • M. canis
  • APproximately 30-70% of stains can fluoresce
  • Infected hairs turn apple green due to tryptophan metabolites on infected hairs
112
Q

Can you get false negatives and/or false positives with Wood’s lamp?

A

-yes to both

113
Q

What can cause false positives with a Wood’s lamp?**

A
  • Medication on hairs

- Scales/crusts or scales/crusts on hairs

114
Q

What is the gold standard test for diagnosis of dermatophytosis?

What does this test offer you in terms of a diagnosis?

A
  • Fungal culture
  • Reliable method to make definitive diagnosis
  • Helps ID species and dermatophyte and source of infection
115
Q

What does fungal culture detect?

A
  • Presence or absence of fungal spores on hair coat
116
Q

How long does fungal culture take?

A
  • 1-3 weeks

- Positive growth can generally be esen in 1-2 weeks but some species can take 3 weeks to grow

117
Q

Collection technique for fungal culture?

A
  • Mackenzie toothbrush technique***
  • Pluck hairs from periphery of active lesion
  • Scrape periphery of active lesion with sterile scalpel
118
Q

Mackenzie toothbrush technique

A
  • Brush entire cat with sterile toothbrush to collect hairs and spores (head to tail)
  • Touch toothbrush to media and also transfer hairs from toothbrush to media with hemostats
119
Q

What media is used for dermatophytosis?

What is the indicator?

A
  • Dermatophyte test media
  • Nutrient medium plus inhibitors of bacterial and saprophytic growth
  • Phenol red is pH indicator
120
Q

How to do a fungal culture?

A
  • Media turns red at the first evidence of colonization
  • Monitor daily for color change and colony growth
  • Usually the colony starts growing in 10-14 days
121
Q

Dermatophyte colony appearance vs saprophytic fungal appearance

A
  • Dermatophytes are white to light tan or buff

- Saprophytics produce a green to black (pigmented) color/colony growth

122
Q

Stained slide preparation

A
  • Examien all suspect colonies
  • To a microscope glass slide, add lactophenol cotton blue stain
  • Pickup surface of colony with clear acetate tape
  • Spread tape on glass slide
  • Examien for macroconidia
  • ID of a dermatophyte macronidia from a culture plate = definitive
123
Q

Where are dermatophyte macroconidia found?

A
  • Only on culture plates, not on animals
124
Q

PCR for dermatophyte - how sensitive?

A
  • Very sensitive
125
Q

PCR for dermatophyte - speciment collection?

A
  • Mackenzie toothbrush technique
126
Q

Turnaround time for dermatophyte PCR?

A
  • 2-3 days
127
Q

Specificity of PCR for dermatophytes

A
  • False positives can occur
  • Dead organisms from successfully treated infection?
  • Noninfected fomite carrier
128
Q

What does a negative PCR in a treated cat mean for dermatophytosis?

A
  • Mycological cure!
129
Q

SKin biopsy for fungal dermatophytosis?

A
  • Not a routine diagnostic tool!

Dermatophytes infect the hair follicle and can live there

  • Looks like folliculitis
  • This won’t tell you the species

Dermatology (15 decks)

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