What is commonly referred to as mange in dogs actually can be caused by a couple of different microscopic parasites called mites. Demodex canis mites are commonly found in limited infestations on almost all animals and typically do not cause serious problems. Demodectic mites do not cross-infect with other animals and therefore are more easily managed than their frustrating cousins, Sarcoptes scabei.
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Sarcoptic Mange
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Sarcoptic mange is caused by an infestation of the mite Sarcoptes scabei, a mite found throughout the world. Domestic dogs in the U.S. often are infected with this mite by direct contact with infected foxes. However, infection from indirect contact--either the dog goes near the den of an infected animal or the infected fox comes into the dog's territory--also occurs. It is highly contagious from dog to dog. Cats are rarely infected with sarcoptic mange, although they get mange from a different mite.
Life Cycle
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The sarcoptic mite spends its entire life cycle of 17 to 21 days on the dog. Females burrow into the skin and lay their eggs, which causes inflammation of the skin and intense itching by the dog as a response.
Symptoms
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Intense itching by the dog is an indicator of possible scabies infection. Certain areas such as the ear flaps and elbow area on the front leg are common sites for the mites to infect since these areas are difficult for the dog to reach. The dog's dramatic itching will cause inflammation of the skin, pus and resulting crusty areas. While the mite cannot live on humans, it will spend a couple days on human skin, resulting in red welts; this can be further indication of a scabies infection.
Detection
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Positive findings are difficult for sarcoptic mite infection. Domestic pets are often well groomed so skin scrapings can result in no findings. A veterinarian will do skin scrapings for potential diagnosis under a microscope; these scrapings need to be quite deep in order to get to the point under the skin to which the female mites burrow.
Treatment
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Treatment is critical. Foxes in the wild die of mange infections--they are literally driven to distraction by the itching, become lethargic and indifferent to eating. Young, healthy domestic dogs rarely get to this point since they are healthy enough to ward off severe infection and are typically well groomed. However, the mites do not go away without treatment. Most dogs can be treated with drugs such as selamectin as well as ivermectin and moxidectin (both of the latter of which would be considered "off-label" use for treating mites). Take your dog to the veterinarian immediately if you suspect signs of scabies. Do not self-treat as some dog breeds cannot tolerate some drugs; for example, collies cannot be given ivermectin in doses high enough to kill mites. Also, since scabies is difficult to diagnose, your dog may be dealing with a different problem that needs different treatment.
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