Demodicosis (Red Mange) in Dogs

Demodicosis, also known as red mange or "demodex", is a common skin disease of dogs caused by a microscopic mite called demodex canis. These mites are part of the normal flora of the skin, and are present in small numbers, so the disease is not contagious. In predisposed individuals the mites increase in number causing clinical disease.

Why some dogs develop demodicosis and others don't is not understood. It is thought to be genetic; affected dogs have an immune system defect that may be inherited, making it difficult to keep the mites under control.

There are different forms of this disease: localized and generalized.

Localized 

This form usually occurs in dogs younger than one year of age. There is no breed or sex predilection. Affected animals are usually healthy and have developed demodicosis as the result of a temporary illness or a stressful event. 

The first sign of localized mange might be thinning of the hair around the eyelids, lips, mouth and the front legs – a typical moth-eaten appearance. Prognosis is usually very good, and most animals (90 percent) will recover spontaneously. About 10 percent usually will become generalized.

Generalized 

Generalized demodicosis can begin as a localized case or can present itself as an acute illness. It is frequently categorized according to the age of the dog during the initial onset (juvenile or adult). The main distinction between the two types is the result of differences in predisposing factors and prognosis.

Juvenile-onset generalized demodicosis has a more favorable prognosis. Most of them will "self cure" as their immune system matures, somewhere between eight months and three years, depending on the breed of the dog.

Adult-onset generalized demodicosis has a more guarded prognosis. These animals develop demodicosis as a consequence of another illness or immunosuppressive therapy. They do not have a genetic predilection for demodicosis. Conditions associated with adult onset demodicosis include cancer, endocrine disease, metabolic disease or steroid therapy. Prognosis depends on the underlying disease.

For the generalized form, a genetically inherited predisposition to the disease has been found. For this reason, affected animals should be neutered. Both females and males have the same ability to transmit genetic predisposition to demodicosis. The generalized form of the disease is much more difficult to resolve with therapy and relapses after discontinuation of therapy are common. 

What to Watch For

Clinical signs consist of demodicosis consist of numerous patches that appear on the head, legs and trunk. These patches generally develop into large areas of hair loss, and the breakdown of skin leads to the formation of crusty sores.