Demodectic Mange (also called Demodicosis) is a skin disease of dogs caused by the skin mite Demodex canis. The cigar-shaped mites live inside hair follicles and are normally passed from mother to pups at a young age. In small numbers, demodex mites are not considered pathologic and do not cause disease.
Because of genetic factors and/or disorders of the immune system, the skin mites may increase in number and lead to the development of skin problems. Symptoms typically include hair loss, redness of the skin, and recurring skin infections.
Two forms of demodicosis exist. "Juvenile-onset" afflicts dogs younger than 18 months and "Adult-onset" afflicts dogs older than 18 months. This distinction is drawn because juvenile-onset demodicosis usually carries a better prognosis. Demodicosis is further classified as "Localized" or "Generalized." The disease is generalized if two or more feet are affected, if five or more localized lesions are present, or if an entire body region is affected.
The localized form of juvenile demodicosis is considered benign and usually does not require treatment. Most cases resolve within 2-3 months as the immune system develops and fights off excessive numbers of mites. Localized lesions are usually relatively small hairless, red, scaly, lesions. Some cases develop into generalized demodicosis, which is characterized by hair loss, crusting, and inflammation affecting most or all of the body. Besides genetic and immune causes, other causative factors include poor nutrition, parasitic infections, and heat cycles. While some of these generalized cases will recover spontaneously without treatment, we typically recommend treatment to facilitate quicker recovery.
Adult-onset generalized demodicosis is a serious disease because it may be an indication of internal disease that is suppressing the immune system. Cushing's Disease, hypothyroidism, systemic disease/organ dysfunction, and cancer are all possible underlying causes. Diagnostic tests to look for these underlying causes are generally warranted.
Demodicosis is diagnosed by obtaining deep skin scrapings and observing the mites under the microscope. Skin scrapings are obtained by squeezing a portion of affected skin to help express the mites from hair follicles. The side of a scalpel blade is then scratched along the skin to collect a representative sample of the deeper skin structures. A skin scraping will result in a small raw area on the skin. Although a little uncomfortable, most dogs tolerate the procedure very well. In thick-skinned dogs such as the Shar Pei, skin biopsies are usually necessary since it is difficult to obtain mites from a skin scraping.
As mentioned above, localized disease may not require treatment.
Generalized demodicosis is a serious disease and must be treated aggressively with drugs to control the mites and the secondary bacterial infection. The younger the dog, the better the chance for cure. Generalized adult-onset disease, however, may be controlled but cure is not always possible. Some cases can never be controlled.
The mainstay of therapy is a special dip called amitraz (Mitaban®). This product can have serious side effects, and directions from your veterinarian should be followed closely. We typically recommend bathing with a benzoyl-peroxide shampoo prior to dipping to help flush the hair follicles. The dip should be mixed with water according to your doctor's instructions prior to use. Application of the dip should be in a well-ventilated area. Prior to dipping, a protective ointment should be applied to your pet's eyes. Rubber gloves should be worn by the person applying the dip. The dip should be applied with the dog standing in a bathtub. Using a sponge, the mixture should be applied to thoroughly saturate the skin. Continue to reapply the runoff with a sponge for 15 minutes. Do not rinse off the dip. Allow the dog to air dry. Your dog should not be allowed to become wet (including the feet) between dip treatments. Dipping is typically performed every 1 - 2 weeks as directed by your veterinarian. Fresh dip should be prepared prior to each treatment; do not save dip for later use. Amitraz can cause lethargy, skin irritation, scratching, loss of appetite, vomiting, and diarrhea. On occasion, additional therapy may be warranted if side effects are serious. The person applying the dip should take care to wash up well after applying the dip, since the dip can cause toxic symptoms in humans as well. Dipping is typically continued 1 - 2 months beyond when demodex mites can no longer be found by skin scrapings.
Antibiotics are also an important component of therapy since secondary bacterial infection is a common problem.
Reevaluation is usually done every 4-6 weeks. Skin scrapings are obtained at each visit to monitor effectiveness of treatment. It is critical to follow through with the treatment until the doctor tells you to stop. Recheck exams are usually recommended after stopping treatment to monitor for recurrence.