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248 Dermatophytosis

colony is first visible. NOTE: Color change
in the medium may be delayed 24-48
VetBooks.ir Dermatophyte colonies are never black,
hours in specimens from treated animals.
gray, green, or multicolored.
○ All suspect colonies must be microscopi-
cally confirmed using lactophenol cotton
blue stain or methylene blue. It is helpful
to make the mount and allow it sit for
10-15 minutes before examination, which
helps highlight the macroconidia.
Advanced or Confirmatory Testing
Skin biopsy is not needed for routine diagno-
* sis, and if dermatophytosis is identified, the
presentation was likely atypical. Polymerase
chain reaction (PCR) testing is highly specific
DERMATOPHYTOSIS Same cat. Wood’s lamp shows extent of facial lesions and fluorescence of dermatophytosis and highly sensitive. It is important to submit
lesions not observed in white light (arrows). One fluorescent tube of the Wood’s lamp is visible diagonally at adequate amounts of hairs and crusts for testing
the bottom of the image (asterisk). (Copyright Alana Canupp.)
but only from the lesion site.
TREATMENT
• Commonly overlooked infection sites include ○ Using mineral oil, gently scrape hairs from Treatment Overview
paws, periocular area, ear and inside the bell lesion margins and center of lesion. Pluck This disease will spontaneously resolve without
of the ear, tail, ventrum, and axilla. Wood’s lamp–positive hairs in the direc- treatment, but treatment is recommended to
• Wood’s lamp examination tion of growth, transfer to glass microscope shorten the course of infection and minimize
○ M. canis is the only veterinary pathogen slide, add mineral oil and a coverslip, and transmission to other animals and people.
of clinical significance that glows when examine. Do not use clearing agents. Both topical and systemic therapy are used
exposed to 320-400 nm ultraviolet (UV) Infected hairs are easily seen, even under together.
light. Positive fluorescence is apple green a 10× objective because they are wider
and is found only on the hair shaft. It and pale. If there is any confusion or hairs Acute General Treatment
is due to a fungal metabolite (produced cannot be found, holding the Wood’s lamp Reasonable confinement:
while the hair is growing) that is very over the slide can reveal glowing hairs. • Reasonably confine pet to a room that is
stable; hair samples have remained Wood’s ○ Microscopically, ectothrix spores appear easily cleaned but that still allows for activity
lamp positive for >18 years. Fluorescence as numerous, refractile, spindle-shaped and exercise. This disease is most common in
is an inherent property of M. canis. bodies in cuffs around the hair shaft. animals during critical socialization periods,
Evidence-based review showed that in • Fungal culture and human contact and socialization are
untreated animals, 91%-100% of M. ○ Use soft-bristled toothbrush, and focus necessary to prevent lifelong behavioral
canis lesions fluoresced. on collecting specimen from the lesion(s). problems. Confinement is primarily done
○ Use Wood’s lamp with built-in magnifica- Comb target sites 20 times or until to minimize the areas that need cleaning.
tion. Do not use a black lamp. hairs are visibly trapped in the bristles. • It is not acceptable to cage or crate animals
○ Wood’s lamps do not need to be warmed Wrap head of toothbrush in plastic for the duration of treatment.
up. bag, and place entire toothbrush into a Cleaning:
○ Do allow several minutes for examiner’s second bag. • Primary reason for cleaning is not to
eyes to adapt to low light. ○ The optimal fungal culture medium is prevent disease transmission but rather to
○ Hold Wood’s lamp close to skin (2-4 cm), one that can be easily inoculated with a minimize false-positive fungal cultures or
and move slowly, starting at the head. toothbrush; small plates used in human PCR tests.
This is important to minimize distracting laboratories, glass jars, or “diagnosis by • Change bedding daily. Laundry can be
fluorescence from scales and debris on the color” products are not recommended. decontaminated by washing in domestic
coat and maximize seeing lesions. ○ Inoculate the plate by stabbing the bristles washing machine on long wash cycle. Avoid
○ Only the hair shaft fluoresces, never the in the medium; if agar is seen on the overloading the machine. Bleach and hot
crusts or nails. Newly infected hairs are bristles the technique is adequate. Do not water were no more effective than cold water
very short and often obscured by crusts overinoculate the plate because it inhibits without bleach.
(lift crusts as needed). The target color sporulation, and all that will be seen is • Mechanically remove shed hairs and debris
is apple green; blue fluorescence of scale hyphae. daily using disposable dust cloths or washable
and dull yellow fluorescence of excessive ○ Always place plates in plastic bags to floor dusters.
sebum (chin, tail) should not be mistaken prevent cross-contamination and infesta- • Wipe contaminated surfaces daily with a
for dermatophytosis. If in doubt, examine tion with media mites. one-step ready-to-use bathroom cleaner
hair bulb by plucking hair or strip a ○ Optimal growth and sporulation occurs labeled as efficacious against Trichophyton
lesion with clear acetate tape to collect at 80°F (28°C); light conditions do not mentagrophytes.
sample. matter. Fourteen days is adequate for • Twice weekly, wash target surfaces with
• Direct examination holding plates for untreated animals soap and detergent, rinse, and dry. Area
○ More than 85% of dermatophyte infec- (99% positive) and treated animals should be visibly clean. Most surfaces can
tions (M. canis, M. gypseum, Trichophyton (98% positive). Examine the plates daily be decontaminated with aggressive washing
spp) can be confirmed by direct examina- for growth. Look for a whitish, fluffy to with a detergent. Judiciously use a ready to
tion of combined skin scraping and hair powdery colony, with a red color change use bathroom disinfectant (see above) to kill
plucking. in the medium at the same time that the spores on surfaces.

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