Dermatophytosis Flashcards by Brittany Jermalovic

Dermatophytosis

Background

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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Dermatophytosis

Zoophilic

Primarily infected animals vs. man but still zoonotic

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

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Dermatophytosis

Geophilic

Inhabits soil
Decompose keratinaceous organic debri

M. gypseum

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Dermatophytosis

Anthropophillic

Primarily infects man rarely animals

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Clinical incidence of Dermatophytosis

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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Dermatophytosis

Transmission

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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Dermatophytosis

Pathophysiology

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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Dermatophytosis
Clinical Signs
M. canis

Well adapted species

Minimal inflammation with alopecia in cats

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

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Dermatophytosis
Clinical Signs
M. gypseum
T. mentagrophytes

Less well adapted species

More marked inflammation with alopecia

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Generalized Canine Dermatophytosis

Lesions

Papules
Pustules
Vesicles

Pruritus variable

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Dermatophytosis

Immunology

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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Canine dermatophytosis
Clinical signs (common)

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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Canine dermatophytosis

DfDx

Superficial pyoderma
Demodicosis

Remember this condition is rare in dogs

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Canine dermatophytosis

Other clinical signs

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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Canine dermatophytosis

Kerions caused by

M. gypseum
Trichophyton sp.

Geophilic!

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Canine dermatophytosis

Onychomycosis caused by

T. mentagrophytes

Feline dermatophytosis

Background

M. canis most common

Can become endemic in some catteries

Will be Wood’s lamp (+)

Feline dermatophytosis

Rules to live by

All long-haired cats have dermatophytosis until proven otherwise

All cats should be checked for dermatophytosis before being adopted

Feline dermatophytosis

Clinical signs

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

Feline dermatophytosis

DfDx

Pemphigus foliaceous

Dermatophytosis
Treatment
Topical

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

Dermatophytosis
Treatment
What to avoid

STEROID products

Also do not need an antifungal+antibacterial

Dermatophytosis

Multifocal-Generalized lesions

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

Dermatophytosis
Systemic Treatment
Length of Tx

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

Dermatophytosis Treatment Itraconazole

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

Dermatophytosis Treatment Terbinafine

Excellent! Inhibits squalene expoxidase (effects production of ergosterol) and disrupts fungal cell membrane Stores in adipose tissue Requires high dose; aggressive

Dermatophytosis Treatment Fluconazole

Poor efficacy against Dermatophytosis but may work Less side effects than azoles and terbinafine

Dermatophytosis Treatment Ketoconazole

Not considered effective Can cause liver toxicity Must be given on empty stomach; preferably right before a meal

Dermatophytosis | Environmental control

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

Dermatophytosis Diagnosis Wood's Lamp

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

Dermatophytosis Diagnosis Fungal culture (KNOW)

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

Dermatophytosis Fungal culture Media

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

Dermatophytosis | Fungal Culture Step 2

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)

Dermatophytosis | PCR

PCR negative on a treated cat = mycological cure Collect specimen via toothbrush