Scabies, tiny spiderlike mites, are highly contagious and are transmitted primarily by direct contact and through contaminated grooming equipment and kennels. These mites are also transferable to humans and other pets.
Probably no other skin disease will cause your dog to scratch and bite at her skin with such intensity. The severe itching is caused by female mites tunneling a few millimeters under the skin to lay their eggs. The eggs hatch in 3 to 10 days. The immature mites develop into adults and begin to lay eggs of their own. The entire life cycle occurs on the dog’s skin, and takes just 17 to 21 days.
Scabies attacks the skin of the ears, elbows, hocks, and the underside of the chest and face. The onset is abrupt with scratching, hair loss, and inflamed skin in these areas. Crusty ear tips are characteristic. A classic test for scabies is to rub the ear flap between your fingers and watch the dog scratch on the same side. In the later stages the skin becomes thick, crusted, scaly, and darkly pigmented.
Scabies in people can produce an itchy rash, typically found at the belt line. This rash is caused by insects that have transferred from the dog. Scabies mites, however, do not live on human skin for longer than three weeks. If the problem does not disappear in three weeks, look for a continuing source of infestation.
The diagnosis is made by examining skin scrapings under a microscope. In some cases the mites may not be identified. If the dog’s symptoms strongly suggest scabies, your veterinarian may decide to begin treatment as a diagnostic test. A positive response to the treatment confirms the diagnosis of scabies.
Treatment: Scabies must be treated under veterinary supervision. Clip the hair away from scabies-affected areas on medium and longhaired dogs and bathe the entire animal using a benzoyl peroxide shampoo (such as OxyDex or Pyoben). The shampoo loosens scales and makes it possible for an insecticide dip to penetrate the hair pores.
Scabies mites have developed resistance to a number of organophosphate dips. Two dips that remain active against them are amitraz (brand name Mitaban) and 2 to 4 percent lime-sulfur (LymDyp). Only lime-sulfur is licensed by the FDA to treat scabies in dogs. However, LymDyp has an unpleasant odor, stains white coats, and can irritate the skin.
Dip the dog once a week for six consecutive weeks (or until the symptoms resolve), using the dip recommended by your veterinarian. Continue treatment for two more weeks after the dogs appears to be cured. When using any dip, carefully follow the instructions on the label. For information on how to dip, see Insecticide Dips. It is important to treat all dogs who have come into contact with the affected individual.
Oral ivermectin is effective against scabies and is frequently used as a diagnostic test when skin scrapings have been negative. Ivermectin, in doses used for scabies, has produced central nervous system problems and deaths in Collies, Shetland Sheepdogs, Old English Sheepdogs, Australian Shepherds, and other herding breeds and their crosses. The drug is contraindicated in these breeds at the higher dosages. Dogs of these breeds made be tested for the MDR 1 (multi-drug resistance) gene by having your veterinarian send a cheek swab to Washington State University College of Veterinary Medicine.
Always have the heartworm status of your dog checked before giving ivermectin, because it may cause a reaction in dogs who are positive for the heartworm larvae. Recent reports suggest that Interceptor (milbemycin oxime) may also be effective against scabies mites, and could be used instead of ivermectin in breeds in which ivermectin is contraindicated. Revolution (selamectin) is also labeled to help in preventing and treating sarcoptic mange in dogs.
Corticosteroids relieve severe itching and may be required for the first two to three days of treatment. Infected skin sores require oral and topical antibiotics. Adult mites can live for 21 days off the host.
Treatment of the indoor environment (as described in Eliminating Fleas on the Premises) is advisable to prevent recurrence.