Demodectic mange, also called "demodicosis," "Red Mange" "Demodicosis" mange is caused by a microscopic mite of the Demodex genus. Three species of Demodex mites have been identified in dogs: Demodex canis, Demodex gatoi, and Demodex injai. The most common mite of demodectic mange is Demodex canis.
All dogs raised normally by their mothers possess this mite and that occurs naturally in the hailr follicles. As mites are transferred from mother to pup via cuddling during the first few days of life and suckling her milk. Demodectic mange is not contagious after weaning. Most dogs live in harmony with their mites, never suffering any consequences from being parasitized. If, however, conditions change to upset the natural equilibrium (such as intense stress, or malnutrition), the Demodex mites may "gain the upper hand." The mites can reproduce rapidly, causing symptoms in sensitive dogs that range from mild irritation and hair loss on a small patch of skin to severe and widespread inflammation, secondary infection, and—in rare cases—a life-threatening condition. Small patches of demodicosis often correct themselves over time as the dog's immune system matures, although treatment is usually recommended.
Many puppies will grow out of demodectic mange as their immune systems mature. Demodectic mange can re-occur if the immune system is compromised such as after steriod treatment or other immune-compromising illness. Treatment with ivermectin is often prescribed by vets along with skin scrapings. Ivermectin is often continued until two negative skin scrapings are achieved.
Demodectic mange (unlike Sarcoptic mange) is not considered a contagious disease and isolation of affected dogs is generally not considered necessary. That said, there are some circumstances under which the mites could spread from one dog to another.
Classically Demodex mites have been felt to only be transferable from mother to newborn pup. After the pup is a week or so old, it has developed enough immunity so that infection is no longer possible. In other words, after age one week or so, a dog will not longer accept new mites on its body.
Recently this idea has been challenged as occasionally multiple unrelated dogs break with demodicosis in the same household. It is not clear if some species of Demodex are more contagious than others or if some contagion is possible under certain circumstances. Current thinking is that mites actually can be transferred from one dog to another but as long as the dog is healthy, the mites simply add into the dog's natural mite population and no skin disease results. Isolation of dogs with even the most severe demodicosis is still felt to be unnecessary; though, in rare circumstances contagion is possible. While there are still assorted theories about dog to dog transmission of Demodex mites, there is no question that mites cannot be transmitted to humans or to cats.