Dermatophytosis Flashcards
What causes dermatophytosis? (3)
The main pathogens are dermatophytes:
* Microsporum canis (90% cases)
* Microsporum gypseum
* Trichophyton mentagrophytes
Dermatophytosis is a superficial mycosis that is caused by dermatophytes in the epidermal stratum corneum, nails, hairs.
What species or individuals get dermatophytosis?
Most mammals and birds can get it.
Persian cats, Jack Russels, Yorkshire terriers are predisposed.
More in young animals, immunosupressed animals, long-haired cats (asymptomatic).
Higher prevalence in warm and humid climates.
Pathogenesis of dermatophytosis.
Transmitted through direct contact, through environment.
M.Canis with spores attached to hair, M.gypseum
from soil. Trichophyton direct contact (rodents).
Spores survive in environment for a long time (up to two years).
Infection is predisposed through injuries, maceration, clipping micro injuries. The hair in anagen (active growth phase) are more predisposed.
Zoonosis!
Telogen: Resting phase
What helps to defend against dermatophytosis?
Desquamation so renewal of the epidermis. Dermatophytes attach to keratin so when its shed, so are the spores.
A Dry environment.
Telogen (resting phase) hair (less keratin is produced, dermatophytes need growing hair).
Sweat and sebaceous glands reduce dermatophytes.
What does dermatophytosis look like?
It’s often overdiagnosed in dogs and sometimes unnoticed in cats.
Pruritus is rarely seen (sometimes in cats, or if other diseases like allergy are present).
Dogs: alopecia, scales, crusts, papules, pustules. Rarely folliculitis, furunculosis, seborrhea, kerion (an abscess caused by fungal infection), onychomycosis (nail fungus). Usually on face, ear pinna, paws, tail.
Cats: alopecia, that can be scaly, comedones, erythema, miliary dermatitis (can cause pruritus), onychomycosis, acne.
Cats with dermatophytosis always need systemic treatment, dogs can manage with topical when it comes to dermatophytosis. Why?
mostly comes down to how the infection behaves in each species, their grooming habits, and the extent of the infection.
Cats more frequently get widespread or multifocal lesions — not just a small patch here and there. Topical alone often isn’t enough to tackle the whole problem.
Cats are fastidious groomers, and they can spread the spores all over their bodies during grooming. A systemic antifungal helps control the infection from the inside out.
Dogs often have ringworm in just a few spots, which can respond well to topical antifungals.
HYPOPIGMENTATION, SEASONAL FLANK ALOPECIA
might look like dermatophytosis but in this case is not
How is dermatophytosis diagnosed in dogs?
No gold standard! We can find spores, but not the disease.
- Anamnesis, clinical examination
- Wood’s lamp (only Microsporum canis glows under the lamp, the other spp. don’t)
- Skin scrape/trichogram
- DTM
- PCR
- Histopathology
Wood’s lamp
UV Lamp, let it warm for 5-10 min
Used to find infected hair in dermatophytosis Only M.
Canis and 50% cases will glow (up to 90%).
Can’t be used to rule out disease!
Infected hair must have apple green fluorescence!
Be critical about positive lesions - microscope, DTM.
Keratin will glow, crusts will glow, creams, shampoos may leave stains, fibers will glow and give false positives…
Skin scrape/trichogram for dermatophytosis.
If dermatophyte spores are found in microscopy, you can start treatment right away.
Use oil and cover slide. Infected hair are thicker, structure is lost. Spores look like globes. Neg results don’t rule out the disease!
PCR for dermatophytosis.
To find dermatophyte DNA (also dead DNA).
Is Quick!
Can be used to rule out the disease. Toothbrush with sample can be sent to the lab.
Not reliable.
Histopathology (biopsies) for dermatophytosis.
In case of atypical clinical presentation, nodules.
Needs specific staining.
Can be used to diagnose infection on an animal.
Can’t be used to identify species.
How is dermatophytosis txed?
It may self-resolve in 3 months.
In dogs: Topical treatment
* enilconazole
* 2-4% clorhexidine
* clorhexidine + miconazoel shampoo
* antifungal creams like terbinafin, clotrimazole etc.
In cats: Systemic treatment
* itraconazole 5-10mg/kg
* terbinafin 30-40mg/kg
Pulse therapy (week on, week off) 3 courses might be enough.
Biocan M (vaccine) – not suitable for monotherapy or prevention but used in conjunction with other tx to help aid resolution faster.
Environmental tx for dermatophytosis.
Spores don’t multiply in the environment They are stuck to the hair!
Normal cleaning.
Vacuum cleaners (filters)
Heat/steam
Disinfection (enilconazole, bleach, VirkonS). If you can wash it, you can disinfect it. Wash what can be washed (twice) to remove hair with spores stuck to it.
Duration of dermatophytosis tx.
Usually the treatment lasts for many months.
After the first negative DTM (after the clinical signs are gone), tx for another 3 weeks. Another DTM 4
weeks after the treatment is stopped.
After 2 consecutive DTM (McKenzie method) taken from 1-3 weeks apart – are negative.
- No new lesions, old ones are resolving.
- Wood’s lamp shows fluorescence only on the tips of the hair.
- Less colonies to no colonies on DTM.
- PCR neg
If not responding to tx, then consider underlying disease?
