Relative sensitivity of hair pluckings and exudate microscopy for the diagnosis of canine demodicosis

This study was designed to compare the sensitivity of deep skin scraping, hair plucking, and exudate microscopy for the diagnosis of canine demodicosis. Sixty-seven dogs diagnosed with demodicosis were enrolled in the study. Thirty dogs had localized and 37 had generalized demodicosis. Twenty-seven of the 67 dogs had complicated (secondarily infected) and 40 had noncomplicated form. On each dog, a single lesion was randomly selected to obtain one deep skin scraping, hair plucking, and, when present (n = 13) exudate. For skin scraping and exudate microscopy, an area under a cover slip measuring 2.2 x 2.2 mm was examined, while trichography included the evaluation of 100 hair shafts. At least one parasitic element was found in 85.1% of trichograms, and 100% of exudate preparations. The number of parasitic elements was higher in skin scrapings compared to the other two methods. The diagnostic sensitivity of skin scrapings was higher than that of hair pluckings for the total number of samples (P = 0.002) and for those obtained from dogs with the localized (P = 0.004) and the noncomplicated (P = 0.002) forms of the disease. The diagnostic sensitivity of hair pluckings was higher in generalized and complicated demodicosis compared to the localized and noncomplicated variants. Based on these results, exudate microscopy may be equally sensitive to deep skin scrapings, and trichography may be of value in generalized and complicated demodicosis, although a negative result cannot rule it out