Diagnosis of canine demodicosis: comparative study between hair plucking and adhesive tape tests

Résumé

Demodicosis is a common parasitary dermatopathy in dogs, resulting from excessive proliferation of Demodex canis mite, a natural inhabitant of dog´s skin. Definitive diagnosis is classically established through microscopic examination of deep skin scrapings obtained from affected areas, in which numerous adult mites and/or immature forms are observed. Although considered as the golden pattern for the disease diagnosis, this technique is difficult to be performed in some parts of the body, as face, eyelids and interdigital areas, besides causing pain in the dog and discomfort to the owner. Two less invasive diagnostic methods, the hair plucking and the adhesive tape test are described. Although these methods are well known, only few studies about their sensitivity were found in the literature. In the present study, tests were conducted on 40 dogs previously diagnosed with demodicosis through deep skin scrapings. At adhesive tape test, 30 of 40 samples were positive, evidencing 75% of sensivity, while at hair plucking, mites were observed in 29 samples, leading to a sensivity of 73%. These results do not differ statistically and suggest that adhesive tape test and hair plucking tests can be used on clinical routine as first choice primary tests for canine demodicosis as they offer more comfort to animal and its owner. Interestingly, the presence of pyoderma raised the sensibility of both tests to 100%. However, deep skin scrapings must be done for diagnosis confirmation whenever the results of these two methods are negative.