Overview
Demodecosis is an inflammatory parasitic disease of dogs characterized by the presence of a high number of mites in the hair follicles, which often leads to inflammation and infection. The mite, demodex, is part of the normal make up of the skin and is normally present in small number. The mite resides in hair follicles and glands surrounding the follicles (sebaceous glands). Due to changes in either the genetic or immune system of the animal, the mite begins to proliferate and causes the clinical signs of the disease.

Canine Demodex
Most cases in dogs occur at a young age. There are no sex or breed predilections. There are two forms of the disease. Transmission occurs by direct contact from the bitch to nursing neonates during the first two or three days of neonatal life. Puppies delivered by cesarean section and raised away from the infected carriers mother will not develop the disease. Adult onset demodex may be due to a decreased resistance to the mite as a result of a compromise of the immune system. It is speculated that some internal disease may cause immunosuppression. The feeling is that there is a subnormal percentage of interlukin-2 receptors on certain blood cells called lymphocytes.

Clinical Signs

Localized Demodex
Signs are usually mild and one to several patches of hair loss and inflammation are noted. The most common sites are the face and fore legs. Most cases heal with less then 10% progressing to generalized demodecosis.

Generalized Demodecosis
There are many lesions. These are reddened patches and may be itchy. Secondary bacterial infections occur as the numbers of mites proliferate.

Differential diagnosis includes primary bacterial infection, fungal infections, contact dermatitis, and immune mediated skin diseases.