44 BASICS
SKIN SCRAPINGS: DEEP SAMPLE
To diagnose infestations ofDemodex canis,Demodex injai,Demodex cati, the technique
is the same as that for a superficial scrape except that an extra step is added.
After the initial material is placed on the slide, squeeze the site between the thumb
and the forefinger, which initiates capillary oozing.
Scrape the area again to collect additional material and place on the prepared slide.
Pressure theoretically forces the mites toward the surface of the hair follicles.
Scan the slide using the 10×objective; adjust the microscope diaphragm and/or con-
denser to provide greater contrast.
Note the proportion of live/dead mites and egg/young/adult forms present
(Figure 5.2b).
Caution: edema and swelling, often seen with pododemodicosis, may make finding
the mites more difficult; sample at the margins of lesions.
TRICHOGRAMS: HAIR PLUCKS
An adjunct to other types of sampling or when obtaining periocular samples.
Place a small amount of mineral oil on a glass slide.
Pluck a small sampling of hairs from lesional and/or perilesional skin with a hemostat
and place directly in the mineral oil;Demodexmites may be seen clustered around the
hair bulb of extracted hairs (Figure 5.3).Place the hairs on the slide in a unidirectional pattern so that all the hair bulbs line
up, making the slide easier to read.
Scan the slide using the 10×objective; adjust the microscope diaphragm and/or con-
denser to provide greater contrast.
Note the number of anagen (growing) versus telogen (resting) hairs (a predominance
of telogen hairs may indicate an endocrinopathy; as an exception, many Nordic breeds
have telogen-dominated hair cycles) (Figure 5.4).Clumping of melanin (macromelanosomes) within the hair shafts may indicate a
color dilution alopecia (Figure 5.5).
Dermatophyte-infected hairs will demonstrate an invasion of the keratin of the
hair shaft by arthroconidia and hyphae, resulting in a pale irregular appearance
(Figure 5.6).SQUEEZE TAPE IMPRESSIONS
An additional technique for identification ofDemodexmites.
Adhesive tape is placed onto the lesional skin and the underlying skin is squeezed for
2–3 seconds and repeated 3–4 times.
Tape is placed onto a glass slide, sticky side down.