Dermatophytosis Flashcards
What is dermatophytosis? Is it a parasite?
- Cutaneous fungal infection
- NO
Where do dermatophyte invade?
- Keratinized structures
- e.g. hair, horns, nails, feathers, cornified epithelium
What should happen with dermatophytosis in healthy animals?
- It should resolve on its own
- This depends on the immune status of the host
Is dermatophytosis zoonotic?
- YES
What are the three classifications of dermatophytosis?
- Zoophilic
- Geophilic
- Anthropophilic
Meaning of zoophilic
- Primarily infect animals vs man BUT can be zoonotic
Zoophilic ringworm
- Microsporum canis
- Trichophyton equinum
- T. mentagrophytes
- T. verrucosum
- M. nanum
Geophilic meaning
- Inhabits soil
- Decompose keratinaceus organic debris
Examples of geophilic fungi
- M. gypseum
Which categories of dermatophyte do veterinarians deal with?
- Geophilic and zoophilic primarily
Anthropophilic meaning
- Primarily infect man and rarely animals
WHat is an arthrospore?
- Infective portion of the organism that causes infection
How does the arthrospore form?
- Forms by segmentation and fragmentation of hyphae
Where does the arthrospore adhere?
- Keratin!
What are the two types of infection for dermatophytosis?
- Ectothrix
- Endothrix
Ectothrix definition
- Infection produced outside the hair shaft
Endothrix definition
- Produced inside the hair shift
Which type of infection is primarily anthropophilic?
- Endothrix
Clinical incidence of dermatophytosis in dogs vs cats
- Common in cats
- Uncommon in dogs
Which genera are responsible for 99% of clinical cases?
- Microsporum and Trichophyton
Which regions have dermatophytosis most commonly?
- Warm, humid, tropical areas
Conditions where dermatophytosis flourishes?
- Poor housing conditions (puppy mills, catteries, pet shops, shelters)
- Warm, humid tropical areas
What can increase likelihood that a dog has a dermatophytosis infection?
- Infected cat exposure
Risk factors for dermatophytosis
- Young animals
- Immune suppression
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
Reservoirs of infection for dermatophytosis
- Cats and rodents
- Asymptomatic carriers
What structures of the epidermis must the dermatophyte invade?
- Keratin of stratum corneum and/or hair
What type of hair does dermatophytosis prefer?
- Anagen hairs (growth phase)
- Growing hairs contain carbohydrates, nitrogenous substances, and nucleoprotein derivatives in addition to keratin
Physical barriers to infection
- Hair
- Stratum corneum
Pathophysiology of dermatophytosis
- Invades keratin of stratum corneum and/or hair
- Only grows in anagen (growing) hairs
- Fungi grow downward to just above the hair bulb
- The hair shaft is weakened and breaks
- Induces hair to enter telogen, and the infection resolves in that hair. By this time, it has spread to a neighboring hair.
- Inflammation expels fungus from the hair and infection spreads peripherally
Incubation for dermatophytosis
4-30 days
What determines the clinical signs associated with dermatophytosis?
- The host’s response to fungus
Well adapted species of dermatophyte
- M. canis
Less well adapted species of dermatophyte
- M. gypseum, T. mentagrophytes
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
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
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
What type of immunity is most protective with dermatophytosis?
- Cell-mediated immunity
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
Clinical signs of canine dermatophytosis
- Often quite variable
- Can be focal, multifocal, or generalized
What should you look for with generalized dermatophytosis?
- Look for underlying immune suppression
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
Major differentials for dermatophytosis
- Pyoderma
- Demodicosis
Dermatophytosis - normally pruritic?
- Not usually
What are two other clinical presentations possible with dermatophytosis?
- Kerions
- Onychomycosis
What is a kerion?
Nodular dermal reaction with ulceration and draining tracts caused by a fungi
Which species of fungi usually cause kerions?
- M. gypseum or Trichophyton sp.
- Often from putting their nose in a hole
What is the pathophysiology of fungal kerions?
- Extreme inflammatory reaction or hypersensitivity to dermal location of fungus
Locations of fungal kerions?
- Face/muzzle/legs
Differentials for fungal kerion
- Histiocytoma
- Deep pyoderma
- Neoplasia
- Demodicosis
What is onychomycosis?
- Infection of keratin at the nailbed
Clinical signs of onychomycosis?
- Abnormal nail growth and brittle nails
- Usually asymmetric
- Usually skin is affected too
Species that causes onychomycosis?
- T. mentagrophytes
How common is onychomycosis?
- Pretty uncommon to rare
How long is treatment for onychomycosis in general?
- 9-12 months
What is the most common species for feline dermatophytosis?
- Microsporum canis (>95%)
Feline dermatophytosis - where can it become endemic?
- Catteries and shelters
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
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
Is dermatophytosis usually pruritic in cats?
- No
What should you think with generalized form of dermatophytosis?
- Think FeLV/FIV and ruling that out
4 Reasons to treat dermatophytosis in cats even though it can spontaneously resolve?
- Zoonotic disease
- Decrease spread to other animals
- Decrease environmental contamination
- Speed recovery from infection
Treatment for a single lesion/kerion (IN DOGS ONLY)
- Spot tx with topical antifungal creams
- Apply 1-2 times a day
- DO NOT USE COMBO STEROID PRODUCTS
- WHole-body treatment with topical dip can be helpful to treat subclinical areas
Examples of antifungals for topical treatment in dogs?
- Miconazole, clotrimazole, terbinafine
Can you spot treat cats?
- NO, never do it
Treatment for multifiocal to generalized lesions
- Consider clipping hair coat (debatable but do it in long-haired cats)
- Treat entire body 2 times per week
- May need systemic treatment
- He typically combines entire body treatment with systemic treatment
- Long haired cats cannot usually be cured with topical therapy alone
Examples of dips that can be used for multifocal to generalized dermatophytosis? Which is best?
- Lime sulfur***
- Enilconazole
- Ketoconazole or miconazole containing shampoos
What is Dr. Mel’s treatment for all animals with multifocal to generalized dermatophytosis and ESPECIALLY CATS?
Topical treatment with systemic treatment
Features of rinses
- Treat entire surface area
- Minimizes rubbing of skin
- Treatment can dry on the skin
Why shouldn’t you use shampoos for treating dermatophytosis?
- Little residual activity
- Washing and rinsing could macerate skin
- Spread of spores increased
Frequency of:
- Lime sulfur dip
- Enilconazole
- Miconazole shampoos
- Twice weekly
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
Enilconazole - who licensed for?
- Dogs and horses
- Effective for cats
Side effects of enilconazole
- GI
- Hypersalivation
- Muscle weakness
- Mildly elevated ALT
- Death (Anecdotal)
- Use e-collar!
Miconazole shampoos
- Synergism with chlorhexidine
- Can also be an effective treatment
Systemic treatments - who gets?
- Multi-focal to generalized lesions
- Cats
- Cases of immune-suppression
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
Which happens first: clinical or mycological cure?
- Clinical cure happens first
What is a mycological cure?
- 2 consecutive negtive fungal cultures, 1 week apart
- OR negative PCR
What do our antifungal treatments tend to target?
- Ergosterol and squalene
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
Azoles - what important enzyme do they impact?
- Affect mammalian cytochrome p450 and can lead to increased to decreased concentrations of other drugs
Itraconazole - good or bad treatment for dermatophytosis?
- Excellent
Where does itraconazole accumulate?
- Adipose tissue and sebaceous glands
Itraconazole compounding
- Avoid
Accepted itraconazole protocol in cats
- 5mg/kg PO alternating weeks
Terbinafine - good or bad treatment for dermatophytosis?
- Excellent
Price of terbinafine?
- Quite inexpensive
Terbinafine MOA
- Inhibits squalene epoxidase and disrupts fungal cell membrane
- Squalene is a precursor for ergosterol
Does terbinafine impact cytochrome p450?
- NO
Where does terbinafine store?
- Adipose tissue
Side effects of terbinafine?
- Increases in ALT, ALP, and GI upset
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
Side effects of fluconazole compared to others
- Overall better side effect profile than azoles and terbinafine
Fluconazole MOA?
- Inhibits ergosterol and disrupts fungal cell membrane
Is absorption of fluconazole impacted by antacids?
- No
Is ketoconazole an effective treatment for dermatophytosis?
- No
Where does ketoconazole accumulate?
- Adipose tissue
Administration instructions for ketoconazole?
- Dissolved by gastric aciditiy and should be given on an empty stomach
Ketoconazole side effects
- Interferes with endogenous cortisol synthesis in dogs and humans
- Higher risk for side effects
Where is ketoconazole metabolized?
- Liver by cytochrome p450
Ketoconazole MOA
- inhibits ergosterol and disrupts fungal cell membrane
Is griseofulvin recommended or not and why?
- No
- Teratogenic, panelukopenia in cats, GI upset, ataxia
Is lufeneron recommended or not and why?
- Chitin synthesis inhibitor
- Ineffective as a treatment and preventative
Are antifungal vaccines recommended or not and why?
- No - do not protect
Why is environmental control important for dermatophytosis?
- Environment is a source of infection and may be the reason for reinfection
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
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
What type of test is Wood’s lamp?
- Initial screening light
What is a Wood’s lamp?
- UV light filtered through cobalt or nickel filter
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
Can you get false negatives and/or false positives with Wood’s lamp?
-yes to both
What can cause false positives with a Wood’s lamp?**
- Medication on hairs
- Scales/crusts or scales/crusts on hairs
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
What does fungal culture detect?
- Presence or absence of fungal spores on hair coat
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
Collection technique for fungal culture?
- Mackenzie toothbrush technique***
- Pluck hairs from periphery of active lesion
- Scrape periphery of active lesion with sterile scalpel
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
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
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
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
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
Where are dermatophyte macroconidia found?
- Only on culture plates, not on animals
PCR for dermatophyte - how sensitive?
- Very sensitive
PCR for dermatophyte - speciment collection?
- Mackenzie toothbrush technique
Turnaround time for dermatophyte PCR?
- 2-3 days
Specificity of PCR for dermatophytes
- False positives can occur
- Dead organisms from successfully treated infection?
- Noninfected fomite carrier
What does a negative PCR in a treated cat mean for dermatophytosis?
- Mycological cure!
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
