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Dermatology > Dermatophytosis > Flashcards

Dermatophytosis Flashcards

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Dermatology Board Prep flashcards
1
Q

Dermatophytosis

Background

A

Cutaneous fungal infection

Dermatophyte invades keratinized strutures (hair, horned, nails, feathers, epithelium) causing superficial fungal infection

Self-limiting disease; may take months to resolve though

Zoontoic!

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2
Q

Dermatophytosis

Zoophilic

A

Primarily infected animals vs. man but still zoonotic

Microsporum canis
Trichophyton equinum
T. mentagrophytes
T. verrcosum
M. nanum
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3
Q

Dermatophytosis

Geophilic

A

Inhabits soil
Decompose keratinaceous organic debri

M. gypseum

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4
Q

Dermatophytosis

Anthropophillic

A

Primarily infects man rarely animals

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5
Q

Clinical incidence of Dermatophytosis

A

Common in cats
Uncommon in dogs in which they get it from cats

Microsporum and Trichophyton are main culprits

Usually in poor sanitation and overcrowded conditions

Younger and immunosuppressed animals

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6
Q

Dermatophytosis

Transmission

A

Direct contact with infected host, fomite (combs, clippers), or environment

Can remain viable for years

Asymptomatic carriers (cats and rodents) can serve as reservoir

Ectoparasites can transmit it especially in catteries and multipet housholds

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7
Q

Dermatophytosis

Pathophysiology

A

Must invade keratin of stratum corneum and/or hair

Grows in anagen hairs; grows downward just have hair bulb (must get into hair follicle)
Hair shaft weakened and breaks
Spreads to neighboring hair
Induces hair to enter telogen; infection resolves in that hair
Inflammation expels fungus from hair and infection spreads peripherally

Incubation: 4-30 days

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8
Q

Dermatophytosis
Clinical Signs
M. canis

A

Well adapted species

Minimal inflammation with alopecia in cats

Marked inflammation (ring-like lesion) in dogs and humans

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9
Q

Dermatophytosis
Clinical Signs
M. gypseum
T. mentagrophytes

A

Less well adapted species

More marked inflammation with alopecia

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10
Q

Generalized Canine Dermatophytosis

Lesions

A

Papules
Pustules
Vesicles

Pruritus variable

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11
Q

Dermatophytosis

Immunology

A

Cell-mediated = MOST important

No correlation between circulating antibodies and protection

Sebum and serum produced in/on skin has fungistatic properties

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12
Q 
Canine dermatophytosis
Clinical signs (common)
A

Variable

Circular patch of alopecia characterized by broken stubby hair, scaling, and mild erythema

Broken stubby hairs that spread peripherally

Focal, multifocal, generalized (immune suppression)

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13
Q

Canine dermatophytosis

DfDx

A

Superficial pyoderma
Demodicosis

Remember this condition is rare in dogs

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14
Q

Canine dermatophytosis

Other clinical signs

A

Kerions; dermatophyte furunculosis
Nodular dermal reaction with ulceration and draining tracts
Extreme inflammatory reaction or hypersensitivity to dermal location of fungus

Onychomycosis
infection of keratin at nailbed
Get abnormal nail growth; brittle nails
Tx for 9-12 months

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15
Q

Canine dermatophytosis

Kerions caused by

A

M. gypseum
Trichophyton sp.

Geophilic!

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16
Q

Canine dermatophytosis

Onychomycosis caused by

A

T. mentagrophytes

17
Q

Feline dermatophytosis

Background

A

M. canis most common

Can become endemic in some catteries

Will be Wood’s lamp (+)

18
Q

Feline dermatophytosis

Rules to live by

A

All long-haired cats have dermatophytosis until proven otherwise

All cats should be checked for dermatophytosis before being adopted

19
Q

Feline dermatophytosis

Clinical signs

A

Patches of alopecia, crusting, scaling

Face and ears but can be focal, multifocal, or generalized

Miliary dermatitis (erythematous crusts throughout the coat)

Usually not pruritic

Asymptomatic carriers most common

20
Q

Feline dermatophytosis

DfDx

A

Pemphigus foliaceous

21
Q

Dermatophytosis
Treatment
Topical

A

Single lesion/kerion
Spot treatment with topical antifungal creams or lotions (do NOT spot treat cats)

Miconazole, clotrimazole, terbinafine

1-2x daily

Whole body treatment with topical dip is helpful to treat subclinical areas of infection

22
Q

Dermatophytosis
Treatment
What to avoid

A

STEROID products

Also do not need an antifungal+antibacterial

23
Q

Dermatophytosis

Multifocal-Generalized lesions

A

Clip hair coat(gently do not cut skin)

Treat entire body 2x/week:
Lime sulfur dip 
Enilconazole (horses, not cats)
Ketoconazole or miconazole shampoos (not most effective)
Place e-collar after dip

Can also put on systemic treatment

24
Q

Dermatophytosis
Systemic Treatment
Length of Tx

A

Multiple lesions, cats, or immunosuppressed patients

Clinical and mycological cure (clinical comes before mycological)

2 consecutive negative fungal cultures, one week apart (negative PCR results)

May take 6 weeks or more

25
Q

Dermatophytosis
Treatment
Itraconazole

A

Excellent!

Avoid compounded fomula

Accumulates well in adipose tissue and sebaceous glands

Low dose = fungi static
High dose = fungicidal

Can treat every other week PO

Can effect CYP450

26
Q

Dermatophytosis
Treatment
Terbinafine

A

Excellent!

Inhibits squalene expoxidase (effects production of ergosterol) and disrupts fungal cell membrane

Stores in adipose tissue

Requires high dose; aggressive

27
Q

Dermatophytosis
Treatment
Fluconazole

A

Poor efficacy against Dermatophytosis but may work

Less side effects than azoles and terbinafine

28
Q

Dermatophytosis
Treatment
Ketoconazole

A

Not considered effective

Can cause liver toxicity

Must be given on empty stomach; preferably right before a meal

29
Q

Dermatophytosis

Environmental control

A

Thoroughly wash, dust, vacuum, scrub, and disinfect all surfaces, drapes, and other objects (challenging)

Must use bleach products (daily with 10 minutes of contact time)

Washing bedding with hot water and bleach

Change air filters and clean vents

Infected animal must be quarantined for 15 days at least

30
Q

Dermatophytosis
Diagnosis
Wood’s Lamp

A

Wood’s lamp = screening test
NOT a blacklight

Will only detect M. canis

False positives:
Medication on hair
Scales/crusts or scales/crusts on hairs

NOT a definitive diagnosis

31
Q

Dermatophytosis
Diagnosis
Fungal culture (KNOW)

A

Detects presence or absence of fungal spores on hair coat

Definitive diagnosis can be obtained; can know species

Can take 1-3 weeks; positive growth can generally be seen within 1-2 weeks

Collect sample via toothbrush; brush entire cat with toothbrush use sterile hemostats to transfer the hair

Can also pluck hairs or scrape periphery of active lesion

Note: during treatment should be doing weekly fungal cultures

32
Q

Dermatophytosis
Fungal culture
Media

A

Dermatophyte Test Media (DTM)

Will turn red at first evidence of colony growth
Can take up to 3 weeks

Colonies are white-tan

Recommends plates rather than the small jars

33
Q

Dermatophytosis

Fungal Culture Step 2

A

Stained slide prep

Take expected colony from DTM and examine it; use acetate tape to pick it up

Stain: lactophenol cotton blue

Looking for: macroconidia (only found on culture plates not on animals)

34
Q

Dermatophytosis

PCR

A

PCR negative on a treated cat = mycological cure

Collect specimen via toothbrush

Dermatology (13 decks)

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