Dermatophytosis Flashcards
1
Q
What is dermatophytosis? Is it a parasite?
A
- Cutaneous fungal infection
- NO
2
Q
Where do dermatophyte invade?
A
- Keratinized structures
- e.g. hair, horns, nails, feathers, cornified epithelium
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
4
Q
Is dermatophytosis zoonotic?
A
- YES
5
Q
What are the three classifications of dermatophytosis?
A
- Zoophilic
- Geophilic
- Anthropophilic
6
Q
Meaning of zoophilic
A
- Primarily infect animals vs man BUT can be zoonotic
7
Q
Zoophilic ringworm
A
- Microsporum canis
- Trichophyton equinum
- T. mentagrophytes
- T. verrucosum
- M. nanum
8
Q
Geophilic meaning
A
- Inhabits soil
- Decompose keratinaceus organic debris
9
Q
Examples of geophilic fungi
A
- M. gypseum
10
Q
Which categories of dermatophyte do veterinarians deal with?
A
- Geophilic and zoophilic primarily
11
Q
Anthropophilic meaning
A
- Primarily infect man and rarely animals
12
Q
WHat is an arthrospore?
A
- Infective portion of the organism that causes infection
13
Q
How does the arthrospore form?
A
- Forms by segmentation and fragmentation of hyphae
14
Q
Where does the arthrospore adhere?
A
- Keratin!
15
Q
What are the two types of infection for dermatophytosis?
A
- Ectothrix
- Endothrix
16
Q
Ectothrix definition
A
- Infection produced outside the hair shaft
17
Q
Endothrix definition
A
- Produced inside the hair shift
18
Q
Which type of infection is primarily anthropophilic?
A
- Endothrix
19
Q
Clinical incidence of dermatophytosis in dogs vs cats
A
- Common in cats
- Uncommon in dogs
20
Q
Which genera are responsible for 99% of clinical cases?
A
- Microsporum and Trichophyton
21
Q
Which regions have dermatophytosis most commonly?
A
- Warm, humid, tropical areas
22
Q
Conditions where dermatophytosis flourishes?
A
- Poor housing conditions (puppy mills, catteries, pet shops, shelters)
- Warm, humid tropical areas
23
Q
What can increase likelihood that a dog has a dermatophytosis infection?
A
- Infected cat exposure
24
Q
Risk factors for dermatophytosis
A
- Young animals
- Immune suppression
25
Transmission of dermatophytosis
- 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
26
Reservoirs of infection for dermatophytosis
- Cats and rodents
| - Asymptomatic carriers
27
What structures of the epidermis must the dermatophyte invade?
- Keratin of stratum corneum and/or hair
28
What type of hair does dermatophytosis prefer?
- Anagen hairs (growth phase)
| - Growing hairs contain carbohydrates, nitrogenous substances, and nucleoprotein derivatives in addition to keratin
29
Physical barriers to infection
- Hair
| - Stratum corneum
30
Pathophysiology of dermatophytosis
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
31
Incubation for dermatophytosis
4-30 days
32
What determines the clinical signs associated with dermatophytosis?
- The host's response to fungus
33
Well adapted species of dermatophyte
- M. canis
34
Less well adapted species of dermatophyte
- M. gypseum, T. mentagrophytes
35
Clinical signs with well adapted species of dermatophyte in cats vs dogs vs humans
- Minimal inflammation with alopecia in cats
| - More marked inflammation (e.g. ring like lesion) in dogs and humans
36
Clinical signs with less well adapted species of dermatophyte in cats vs dogs vs humans
- More marked inflammation with alopecia in dogs, cats, and humans
37
What immunologic factors are at play with dermatophytosis?
- Young vs old individuals
- Serum and sebum are fungistatic
- CMI is most important
- No correlation between circulating antibodies and protection
38
What type of immunity is most protective with dermatophytosis?
- Cell-mediated immunity
39
What is the classic lesion of canine dermatophytosis?
- Circular patch of alopecia characterized by broken stubby hair, scaling, and mild erythema
- Appears to be spreading outward, often with central healing
40
Clinical signs of canine dermatophytosis
- Often quite variable
| - Can be focal, multifocal, or generalized
41
What should you look for with generalized dermatophytosis?
- Look for underlying immune suppression
42
Lesions possible with dermatophytosis
- 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
43
Major differentials for dermatophytosis
- Pyoderma
| - Demodicosis
44
Dermatophytosis - normally pruritic?
- Not usually
45
What are two other clinical presentations possible with dermatophytosis?
- Kerions
| - Onychomycosis
46
What is a kerion?
Nodular dermal reaction with ulceration and draining tracts caused by a fungi
47
Which species of fungi usually cause kerions?
- M. gypseum or Trichophyton sp.
| - Often from putting their nose in a hole
48
What is the pathophysiology of fungal kerions?
- Extreme inflammatory reaction or hypersensitivity to dermal location of fungus
49
Locations of fungal kerions?
- Face/muzzle/legs
50
Differentials for fungal kerion
- Histiocytoma
- Deep pyoderma
- Neoplasia
- Demodicosis
51
What is onychomycosis?
- Infection of keratin at the nailbed
52
Clinical signs of onychomycosis?
- Abnormal nail growth and brittle nails
- Usually asymmetric
- Usually skin is affected too
53
Species that causes onychomycosis?
- T. mentagrophytes
54
How common is onychomycosis?
- Pretty uncommon to rare
55
How long is treatment for onychomycosis in general?
- 9-12 months
56
What is the most common species for feline dermatophytosis?
- Microsporum canis (>95%)
57
Feline dermatophytosis - where can it become endemic?
- Catteries and shelters
58
What are Dr. Mel's rules for feline dermatophytosis?
- All long-haired cats have dermatophytosis until proven otherwise
- All cats SHOULD be checked for dermatophytosis before being adopted into a household
59
Clinical signs for dermatophytosis in cats
- 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
Is dermatophytosis usually pruritic in cats?
- No
61
What should you think with generalized form of dermatophytosis?
- Think FeLV/FIV and ruling that out
62
4 Reasons to treat dermatophytosis in cats even though it can spontaneously resolve?
1. Zoonotic disease
2. Decrease spread to other animals
3. Decrease environmental contamination
4. Speed recovery from infection
63
Treatment for a single lesion/kerion (IN DOGS ONLY)
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
Examples of antifungals for topical treatment in dogs?
- Miconazole, clotrimazole, terbinafine
65
Can you spot treat cats?
- NO, never do it
66
Treatment for multifiocal to generalized lesions
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
Examples of dips that can be used for multifocal to generalized dermatophytosis? Which is best?
- Lime sulfur***
- Enilconazole
- Ketoconazole or miconazole containing shampoos
68
What is Dr. Mel's treatment for all animals with multifocal to generalized dermatophytosis and ESPECIALLY CATS?
Topical treatment with systemic treatment
69
Features of rinses
- Treat entire surface area
- Minimizes rubbing of skin
- Treatment can dry on the skin
70
Why shouldn't you use shampoos for treating dermatophytosis?
- Little residual activity
- Washing and rinsing could macerate skin
- Spread of spores increased
71
Frequency of:
1. Lime sulfur dip
2. Enilconazole
3. Miconazole shampoos
- Twice weekly
72
Lime sulfur dip characteristics
- Rotten eggs
- Effective topical
- Fungicidal on contact
- Safe in newborn kittens and puppies
- Non-toxic
- Let "room air" dry
- E-collar
73
Enilconazole - who licensed for?
- Dogs and horses
| - Effective for cats
74
Side effects of enilconazole
- GI
- Hypersalivation
- Muscle weakness
- Mildly elevated ALT
- Death (Anecdotal)
- Use e-collar!
75
Miconazole shampoos
- Synergism with chlorhexidine
| - Can also be an effective treatment
76
Systemic treatments - who gets?
- Multi-focal to generalized lesions
- Cats
- Cases of immune-suppression
77
How long to treat for dermatophytosis systemically?
- Treat until you have BOTH a clinical cure and mycological cure
- Can take a minimum of 6 weeks
78
Which happens first: clinical or mycological cure?
- Clinical cure happens first
79
What is a mycological cure?
- 2 consecutive negtive fungal cultures, 1 week apart
| - OR negative PCR
80
What do our antifungal treatments tend to target?
- Ergosterol and squalene
81
MOA of azoles
- 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
Azoles - what important enzyme do they impact?
- Affect mammalian cytochrome p450 and can lead to increased to decreased concentrations of other drugs
83
Itraconazole - good or bad treatment for dermatophytosis?
- Excellent
84
Where does itraconazole accumulate?
- Adipose tissue and sebaceous glands
85
Itraconazole compounding
- Avoid
86
Accepted itraconazole protocol in cats
- 5mg/kg PO alternating weeks
87
Terbinafine - good or bad treatment for dermatophytosis?
- Excellent
88
Price of terbinafine?
- Quite inexpensive
89
Terbinafine MOA
- Inhibits squalene epoxidase and disrupts fungal cell membrane
- Squalene is a precursor for ergosterol
90
Does terbinafine impact cytochrome p450?
- NO
91
Where does terbinafine store?
- Adipose tissue
92
Side effects of terbinafine?
- Increases in ALT, ALP, and GI upset
93
Fluconazole - is it a good treatment or not for dermatophytosis?
- 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
Side effects of fluconazole compared to others
- Overall better side effect profile than azoles and terbinafine
95
Fluconazole MOA?
- Inhibits ergosterol and disrupts fungal cell membrane
96
Is absorption of fluconazole impacted by antacids?
- No
97
Is ketoconazole an effective treatment for dermatophytosis?
- No
98
Where does ketoconazole accumulate?
- Adipose tissue
99
Administration instructions for ketoconazole?
- Dissolved by gastric aciditiy and should be given on an empty stomach
100
Ketoconazole side effects
- Interferes with endogenous cortisol synthesis in dogs and humans
- Higher risk for side effects
101
Where is ketoconazole metabolized?
- Liver by cytochrome p450
102
Ketoconazole MOA
- inhibits ergosterol and disrupts fungal cell membrane
103
Is griseofulvin recommended or not and why?
- No
| - Teratogenic, panelukopenia in cats, GI upset, ataxia
104
Is lufeneron recommended or not and why?
- Chitin synthesis inhibitor
| - Ineffective as a treatment and preventative
105
Are antifungal vaccines recommended or not and why?
- No - do not protect
106
Why is environmental control important for dermatophytosis?
- Environment is a source of infection and may be the reason for reinfection
107
How do you effectively control environmental spread of dermatophytosis?
- 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
Treatment of dermatophytosis in multiple cat households/catteries?
- Fungal culture or PCR ALL cats or assume they are all positive
- Isolate and segregate infected and uninfected cats
- Treat all positive cats
109
What type of test is Wood's lamp?
- Initial screening light
110
What is a Wood's lamp?
- UV light filtered through cobalt or nickel filter
111
Which species will fluoresce under Wood's lamp?
- M. canis
- APproximately 30-70% of stains can fluoresce
- Infected hairs turn apple green due to tryptophan metabolites on infected hairs
112
Can you get false negatives and/or false positives with Wood's lamp?
-yes to both
113
What can cause false positives with a Wood's lamp?**
- Medication on hairs
| - Scales/crusts or scales/crusts on hairs
114
What is the gold standard test for diagnosis of dermatophytosis?
What does this test offer you in terms of a diagnosis?
- Fungal culture
- Reliable method to make definitive diagnosis
- Helps ID species and dermatophyte and source of infection
115
What does fungal culture detect?
- Presence or absence of fungal spores on hair coat
116
How long does fungal culture take?
- 1-3 weeks
| - Positive growth can generally be esen in 1-2 weeks but some species can take 3 weeks to grow
117
Collection technique for fungal culture?
- Mackenzie toothbrush technique***
- Pluck hairs from periphery of active lesion
- Scrape periphery of active lesion with sterile scalpel
118
Mackenzie toothbrush technique
- 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
What media is used for dermatophytosis?
What is the indicator?
- Dermatophyte test media
- Nutrient medium plus inhibitors of bacterial and saprophytic growth
- Phenol red is pH indicator
120
How to do a fungal culture?
- 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
Dermatophyte colony appearance vs saprophytic fungal appearance
- Dermatophytes are white to light tan or buff
| - Saprophytics produce a green to black (pigmented) color/colony growth
122
Stained slide preparation
- 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
Where are dermatophyte macroconidia found?
- Only on culture plates, not on animals
124
PCR for dermatophyte - how sensitive?
- Very sensitive
125
PCR for dermatophyte - speciment collection?
- Mackenzie toothbrush technique
126
Turnaround time for dermatophyte PCR?
- 2-3 days
127
Specificity of PCR for dermatophytes
- False positives can occur
- Dead organisms from successfully treated infection?
- Noninfected fomite carrier
128
What does a negative PCR in a treated cat mean for dermatophytosis?
- Mycological cure!
129
SKin biopsy for fungal dermatophytosis?
- Not a routine diagnostic tool!
Dermatophytes infect the hair follicle and can live there
- Looks like folliculitis
- This won't tell you the species
