Demodex spp mites have long been anecdotally considered to be present in skin flora; however, this has not been proven, as it is difficult to find mites on normal skin scrapings. A sensitive real-time PCR was used to look for Demodex spp DNA in the skin of normal dogs. The presence of Demodex spp mites was investigated in 100 dogs from a humane society shelter and 20 healthy client-owned dogs. Hair samples were collected at either 5 or 20 sites. When only 5 skin sites were assayed, mite DNA were found in 18% of dogs; however, when 20 skin sites were assayed, 100% tested positive for mite DNA.

It was not until the development of molecular testing (PCR) that the presence of Demodex spp mites in the flora of healthy dog skin could be proven. In practice, if mites are easily found on a skin scraping, there is a strong probability that the dog has a compromised immune system and is or will be developing generalized demodicosis. More skin scrapings should be obtained from both normal and abnormal areas. If mites are found in both normal and abnormal skin sites, the patient has generalized demodicosis and medical intervention is needed.—Karen A. Moriello, DVM, DACVD

Small Demodex populations colonize most parts of the skin of healthy dogs. Ravera I, Altet L, Francino O, et al. VET DERMATOL 24:168-e37, 2013.