Veterinary Medicine - August 2008 - (Page 447)

6. Follicular casting in hairs plucked from a dog with demodicosis. 7. Using a scalpel blade to obtain skin scrape samples to diagnose demodicosis. 8. Using a metal spatula to obtain skin scrape samples to diagnose demodicosis. this mite histologically in the sebaceous glands of the skin. Demodex injai infection has been observed more commonly in terrier breeds, such as West Highland white terriers, and only a low number of mites may be found on skin scrapings.6 The clinical signs of canine demodicosis are from a folliculitis induced by the overgrowth of mites in the hair follicle. Any other dermatologic condition that results in in ammation of the hair follicle region will cause similar clinical signs. Differential diagnoses for folliculitis include demodicosis, bacterial skin infection (bacterial folliculitis or super cial pyoderma), and dermatophytosis. Diagnosis Canine demodicosis is usually diagnosed by identifying mites in skin scrapings and hair plucks; however, other techniques for obtaining mites may be used. Skin scrapings. Skin scrapings can be performed with a No. 10 scalpel blade (Figure 7) or with the blunt end of a metal spatula (Figure 8). To minimize the risk of a patient being injured during sampling, especially when performed by inexperienced team members, dull the scalpel blade rst on a hard surface or use a metal spatula instead of a blade. Obtain samples from lesional skin. The skin can be squeezed before or during the scrapings to promote extrusion of Demodex mites from the hair follicles. The skin or the scraping instrument can be wetted with mineral oil to better collect the sample. In a long- or medium-haired dog, gently clipping the area to be scraped will minimize the loss of the scraped material into the surrounding hair. Skin scrapings to identify follicular Demodex species mites should be deep enough to result in capillary bleeding. Transfer the scraped material to a slide, and place a coverslip to enhance sample examination and avoid contamination of the microscope objective with mineral oil. To make the mites easier to nd, lower the microscope condenser and decrease the light on the microscope to increase the contrast in the microscope eld. Evaluating the scraped material with the 4X or 10X microscope objectives is suf cient. Evaluate skin scrapings for the approximate number of mites. Look for the presence and proportion of immature vs. adult mites. With an effective treatment plan, a decreasing proportion of immature mite forms may be the rst sign of improvement. The presence of any mites—even dead mites or mite fragments—is considered a positive result. Hair plucks. Hair plucks can be performed with mosquito hemostat forceps to grasp and pull hairs (Figure 9). If alopecic lesions are being sampled, collect hairs from the lesion’s margin. You may squeeze the skin before or during the hair plucks to promote mite extrusion from the follicles. Place the plucked hairs on a glass slide with mineral oil, and add a coverslip. Sample multiple sites in each patient. Hair plucks may be less sensitive in diagnosing canine demodicosis than skin scrapings are,7 but they are useful for areas of the skin that are dif cult to scrape, such as the face and paws. Hair plucks can also be helpful if the sample area is already showing marked hemorrhage from ulceration or draining tracts. In these situations, it may be dif cult to determine how deep to scrape, and it may be uncomfortable for the patient to have skin scrapings performed while awake (Figure 10). Exudative samples. In cases of canine demodicosis with concurrent deep pyoderma, direct examination of the exudate from pustules or stulous draining tracts may also reveal mites. Collect samples by squeezing the exudate onto a glass slide, and add mineral oil and a coverslip. Acetate tape preparations. Acetate tape can be used to detect the super cial canine mite D. cornei. Repeatedly press a piece of acetate tape to the skin and fur, and then lay the tape at on a glass slide for microscopic examination. No mineral oil or staining is needed, but staining will not interfere with visualization of the mite. Lower the condenser on the microscope and decrease the light to increase the contrast in the microscope eld. Evaluate the entire tape sample by using 4X or 10X microscope objectives. VETERINARY MEDICINE August 2008 447

Table of Contents Feed for the Digital Edition of Veterinary Medicine - August 2008

Veterinary Medicine - August 2008 Contents Editors' Note Leading Off ClinQuiz Idea Exchange Practical Matters Diagnosing and Treating Canine Copper-Associated Hepatopathies Canine and Feline Demodicosis CE Form Advertiser Index Product Preview Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - August 2008

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