WSAVA Nov 2021 Proceedings - Flipbook - Page 37
to collect samples. After collecting the samples, pressed the tape onto
the glass slide and examined it under a microscope at the lowest magnification for fleas, lice, and surface mites.
should be viewed under high magnification or oil immersion for types of
organisms and types of inflammatory cells. Occasionally, acantholytic
keratinocytes, neoplastic cells, and mites can be found on cytology.
Ear smear for otic parasites:
Reference:
Use a cotton swab to collect samples from the ear canal. Rolled the swab
onto the glass slide with a small amount of mineral oil, applied coverslip,
and examined with a microscope under the lowest magnification for
Otodectes cynotis and Demodex.
Superficial skin scraping:
Hair should be clipped before scrapings. Apply mineral oil to the skin
before scraping and scrape large areas to increase the chance of finding
the mites. Scrape oil and debris off onto the glass slide. The finding of
one mite, egg, or fecal pellet is diagnostic. Negative results cannot rule
out scabies. Clinicians may attempt to perform a pinna-pedal reflex or
treatment trial on the patient.
1. Miller WH, Griffin CE, Campbell KL. Chapter 2: Diagnostic method. In:
Muller and Kirk’s Small Animal Dermatology 7th edition. Philadelphia, PA:
Elsevier 2013; 57-107.
2. Mattia DD, Fondati A, Monaco M, et al. Comparison of two inoculation
methods for Microsporum canisculture using the toothbrush sampling
technique. Vet Dermatol 2019; 30:60-e17.
3. Moriello KA, Coyner K, Patrson S, Mignon B. Diagnosis and treatment of
dermatophytosis in dogs and cats. Vet Dermatol 2017; 266-e68.
Deep skin scraping:
Apply a small amount of mineral oil on the scalpel blade. Squeeze (pinch)
the skin, scrape a small area in the same direction until capillary bleeding.
Transfer the material onto the glass slide and cover it with a coverslip.
Examine under the microscope at low magnification for Demodex mite.
More than one mite is diagnostic.
Trichogram:
Use a simple forceps/hemostat to pluck the hairs at the base gently. Pull
in the direction of hair growth, place hair on a drop of mineral oil on the
glass slide. Demodex mites may be seen at the area of the root of the
hairs. This method is also useful for finding parasites attached to the
hairs shaft and finding dermatophyte arthrospores and hyphae along the
hair shaft. This method can also help in determining if the hair loss is
from pruritus. Hair infected with dermatophyte will have a swollen and
irregular fuzzy looking at low magnification. Arthrospores and hyphae
can be seen at high magnification. A broken or blunt hair tip will indicate
external trauma.
Wood’s lamp:
Wood’s lamp is a screening tool for Microsporum canis infection. Hair
shafts infected with M. canis should fluoresce. However, some strains will
not fluoresce and will need fungal culture to confirm the disease. Many
false positives can occur from medications, soaps, and bacteria.
Fungal culture:
Collect damaged hairs, crusts, and scales from the lesion and place them
on fungal media (dermatophyte test media [DTM] or sabouraud dextrose
agar). A sterile toothbrush can be used to brush the coat. This method
is called the “Mackenzie brush technique” and is suitable for sampling
asymptomatic carrier cats. After brushing, gently imprint the bristle on
the surface of the culture medium. Do not put all the collected materials
onto the culture medium; this can cause false-negative results from the
overgrowth of saprophytes. Evaluate the culture daily for any change of
the media color. If the color of the media changes simultaneously with
the colony growth, dermatophytosis is suspected. The clinician should
perform further microscopic examinations from the culture to avoid
false-positive color changes and specify the fungus species.
Cytology:
Cytology helps identify the cause of the disease, monitor response to
treatment, determine needs for culture and susceptibility tests, and interpret culture results. There are various techniques for obtaining the cytology sample from the skin (direct impression smear, swab collection, tape
preparation, fine needle aspiration); selecting which method to collect
samples depends on the nature of the lesions and the location. Samples
37