Canine Demodicosis

Demodicosis is a disease caused by Demodex canis, a mite that normally lives in the hair follicles of dogs. These mites pass from the bitch to the nursing pups at about 3 days of age. The mite spends its entire life on the dog and it is not considered contagious to other dogs, cats, or humans. Because of genetic factors and/or disorders of the immune system, the number of mites on the skin may increase dramatically and lead to the development of lesions. The clinical signs associated with demodicosis are highly variable and may include hair loss, redness of the skin, and recurring bacterial skin infections. There are two forms of demodicosis: juvenile onset and adult onset. They are additionally classified as either "localized" or "generalized." The disease is generalized if two or more feet are affected; if five or more small circular areas of hair loss, scale, and redness are seen; or if an entire body region is affected. Dogs with generalized demodicosis should not be bred because the defect in the immune system that allows them to develop the disease is believed to be inherited. Dogs with juvenile-onset demodicosis are younger than 18 months of age at the onset of clinical signs. The localized form of the disease is considered benign and should not be treated because about 80 per cent of these dogs naturally control their own mite population within 2 to 3 months. Some develop generalized juvenile-onset demodicosis with hair loss, crusting, and irritation affecting the entire body. In addition to genetic and immunologic factors, nutritional status, parasitic infections, heat cycles, and other diseases are considered potentiating causes. Adult-onset generalized demodicosis (dogs older than 18 months of age) is a serious disease because it may be an indication of internal disease that is altering or suppressing the immune system. Many of these dogs have received corticosteroids for a prolonged period of time. Clinical signs are similar to those in the juvenile-onset generalized form of demodicosis. Diagnostic tests may be performed to investigate an underlying cause, such as hyperadrenocorticism (excess cortisone production or administration), hypothyroidism, systemic disease or organ dysfunction, and cancer. Chemotherapy or other immunosuppressive drug therapy may also lead to the development of adult-onset generalized demodicosis. Demodicosis is usually diagnosed by obtaining deep skin scrapings and visualizing the mites under a microscope. The presence of more than one adult mite or of immature forms indicates disease. In some breeds, such as the Chinese Shar Pei, and in dogs with chronic disease, especially of the feet, a skin biopsy may be necessary to diagnose demodicosis. Generalized demodicosis is a serious disease and must be treated aggressively with drugs to control the mites and the secondary bacterial skin infections. Treatment of generalized demodicosis consists of identification and correction of possible underlying diseases that have allowed the mites to proliferate as well as specific therapy for the mites and treatment of accompanying secondary bacterial infections. Most treatments for demodicosis require months of intensive therapy. It is not unusual for your veterinarian to prescribe an extended course of oral antibiotics to treat the deep bacterial skin infections that frequently accompany demodicosis. Other treatments are available for demodicosis, but amitraz (Mitaban) is the only treatment for demodicosis that is approved by the U.S. Food and Drug Administration. In any treatment plan for demodicosis, corticosteroids (topical or systemic) are contraindicated. Your veterinarian may recommend that Mitaban dips initially be performed in the veterinary hospital by qualified personnel to ensure that the treatment is performed correctly as well as to observe for side effects. Medium-haired and long-haired dogs should be clipped every 3 to 4 weeks to facilitate adequate penetration of the Mitaban dip. Dogs should be bathed with a benzoyl peroxide shampoo before each dip. The dip is mixed with water according to the instructions given by your veterinarian in a well-ventilated room or outdoors. Rubber gloves should be worn and, using a sponge, the mixture applied thoroughly to saturate the skin. The dip should be applied with the dog standing in a washtub as the dip runoff is reapplied with a sponge for a full 15 minutes. It is important to treat the facial area, ears, and feet as these regions are commonly affected by demodicosis. Dogs that have demodicosis affecting the feet should stand in the dip preparation for a minimum of 15 minutes. The dip should not be rinsed off. Allow the dog to air dry. Your dog should not be allowed to become wet (including the feet) between Mitaban treatments, as this washes off the medication. This procedure should be repeated as directed by your veterinarian. A new mixture must be prepared for each treatment because the drug is unstable when exposed to light and air; for the same reason, any remaining dip should be discarded. The side effects of Mitaban include lethargy, skin irritation, itchiness, loss of appetite, and occasional vomiting or diarrhea. Side effects are more commonly seen in small dogs, especially the toy breeds. If side effects are observed, your veterinarian should be notified. Other drugs can help in the treatment of demodicosis. These systemic drugs are ivermectin and milbemycin. If your dog has not received heartworm preventive on a regular basis, your veterinarian needs to perform a blood test for heartworm disease before administration of either of these drugs. The side effects of ivermectin and milbemycin include decreased appetite, lethargy, weakness, dilated pupils, tremors, vomiting, coma, and death. Usually the more serious side effects occur with ivermectin, but they may also occur with milbemycin. The side effects are rare and usually resolve with discontinuation of the drug. Collies, Shetland sheepdogs, Old English sheepdogs, Australian shepherds, border collies, or their crosses should not be treated with ivermectin. Your dog needs to be evaluated by your veterinarian every 4 to 8 weeks. Skin scrapings are obtained at each visit and treatment usually continues until two or three consecutive skin scrapings have been negative. Treatment is discontinued at this time, and your dog is reevaluated every 3 months for 1 year. Your dog is not considered "cured" until 1 year has passed without visualization of mites on skin scrapings. A small percentage of dogs have chronic demodicosis and may require lifelong therapy. The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.