http://www.thepetcenter.com/exa/dem.html
QUESTION: Is Demodex transmissible to my healthy dog from a dog that is infested?
ANSWER: Healthy dogs are quite resistant to infestations and, as mentioned, may already have a number of mites residing harmlessly in the skin. It is best, though, to not allow your dog to have direct physical contact with a dog that has an active case of Demodex... just to be safe.
Demodex in the dog is a common infestation of the dog’s skin with tiny, cigar-shaped, eight-legged mites. (Human demodex cases do occur but transmission from the dog to a human is quite rare. Nevertheless, human cases of demodex do happen where transmission from a family pet to a human occurs. See a case of demodex in a human below.) The mites reside and feed in the hair follicle and oil glands of the skin. Also called Mange, which is a general term used to A Demodex mite near the edge of the microscope slide... high power view.describe any kind of mite infestation, Demodex is generally less severe than Sarcoptic mite infestation.
Fortunately, most cases of Demodectic mites are self-limiting… that is, the animal is able to arrest the reproduction and growth of the mites and eventually repair the damage they do. Once eliminated, most dogs do not acquire another infestation; the dog’s immune defenses are primed to eliminate any new Demodex mites that happen to find themselves on the dog. However, there are certain individual dogs that, because of genetic programming, do not produce the specific immune factors that will target the mites for destruction. That specific lack of adequate immune defense against the mites is a hereditary aspect of the disease that can predispose an infested dog to a severe, unresponsive case of Demodex. Many veterinarians believe that all dogs have small numbers of Demodex mites residing in the skin and that having a few mites is normal and common. It is when immune related, or nutritional or environmental stresses impact the dog that visible skin lesions from mite infestations become noticeable. Seen most commonly in young dogs, and rarely in cats, Demodex skin lesions are usually transient, but occasionally in certain individuals the mites will totally overwhelm the dog's skin. See the photo below of a year old Doberman Pinscher with severe, generalized Demodicosis that was totally unresponsive to all attempts at treatment. Adult-onset Demodicosis is explained below.