Mixed infestations of Demodex canis and a short-tailed demodectic mite were reported from several countries since late the 1980s. Differentiations based on measurement of the length of this short demodectic mite have been inconclusive until now. Over 500 adult demodectic mites were collected by tape strip and skin scrapings from a 4-year-old intact male Shih Tzu dog with severe juvenile-onset generalized demodicosis. The dog had a mixed infestation of D. canis and the short-tailed demodectic mite. Two studies were performed on the mites. In the first study, 200 mites were divided into two groups based on different morphology. Group 1: mites short body, rounded end of abdomen, one to three fold lines bilaterally on the abdomen. These criteria were used by the investigators to define the ‘short-tailed’ demodectic mite. Group 2: mites with a slender and tapering free body end and no bilateral abdominal fold lines. One hundred mites were counted in each group. In the second study, 298 mites’ measurements were made independent of body shape. Total body length, width and body ratio of gnathosoma plus podosoma (= prosoma) to opisthosoma were measured. The total body length and width did not easily differentiate the two mites. The body ratio plus morphological characteristics of the rounded end of the abdomen appear to be the easiest method to identify the short-tailed demodectic mite in the clinic.
This study was supported by the Association of Veterinary Dermatology, Taipei.