Today I am going to write about Demodectic mange in dogs. Many people mistake demodex for scabies (Sarcoptic mange), but though clinical signs are similar they are two completely different organisms. Scabies is contagious to people and other dogs while demodex is not. All dogs have demodectic mites living on their body. They are typically well controlled by the dog's immune system and cause no problems. Sometimes, however, a dog is born with an immune problem and is unable to suppress the mite OR an older dog gets sick and his immune system is suppressed so much that he can no longer prevent multiplication of the mite.
The mites look like little caterpillars, but can not be seen with the naked eye. Instead people begin to notice patches of hair loss. This is because the mites live down in the hair follicle causing the hair to fall out. The are passed from dog to dog through prolonged contact (typically from mother to pup while they are nursing) and are species specific (meaning people can't get dog demodex). To diagnose demodectic mange the affected area must be scraped down to the dermis (small amount of bleeding) and looked at under the miscroscope. Finding a mite in a normal dog is nearly impossible because there are so few present. Occasionally the mites live deep down (especially on the feet) and a biopsy is necessary to make the diagnosis.
There are two forms of demodex: localized and generalized. Localized demodex is classified as up to six small areas of alopecia (hair loss) generally on the face, head, and forelegs. Generalized demodex is classified as more than six lesion, large affected areas, or involving more than one paw. Localized demodex is a common puppy ailment that typically resolves on its own with or without treatment. Treatment may be necessary if there is secondary infection, but often a rotenone based medication called Goodwinol is prescribed more to make the owner feel that they are doing something though it may shorten the time the lesion is visible.
Generalized demodex is a severe and possibly life threatening condition commonly occurring in dogs less than 18 months of age and in older dogs that have a reason for a suppressed immune system. Fortunately with proper treatment the signs can often be controlled or even completely resolved (until the next time the dog's immune system is suppressed). I have recently seen two cases in the last 6 months. One in a young puppy that was rescued after being abandoned in the middle of winter and another in an elderly dog.
Piper is an absolutely sweet, loving Labrador that was adopted by a friend of mine after she was found abandoned. She was treated when she first got her last January with ivermectin and antibiotics. I saw Piper in June because she had a sever flare up. In a matter of a few days she went from looking like a normal dog to one that you would expect to find slinking in alleys and half starved (she was not and this is a common presentation for the disease). I personally know her owners and they take very good care of her and called me as soon as she started showing signs again. She also healed very quickly and is still being treated to prevent another outbreak.
The most severe case I have seen in an older dog occurred in a 13 year old Labrador retriever. I was called out to see Thunder, because in a matter of 1-2 days he suddenly developed severe bleeding wounds. His owners were afraid that they might have to have him euthanized because he was so miserable.
Fortunately we were able to make a quick diagnosis of demodectic mange with a secondary staph infection and start treating for both. In just a few days he started feeling better, was scratching less and acting more normal. In one month he was already healing very well. Both his owners and I were estatic at his progress. We ended up having to treat him with ivermectin for 2 and 1/2 months and his last skin scraping was finally negative! I unfortunately did not take a picture of him looking normal again.
We looked for the underlying cause of Thunder's outbreak of demodex and were never able to pin point it, but hopefully it was stress or infection induced and won't bother him again.
A point to note is that if you have a dog with a skin problem I recommend asking your vet to perform a skin scrape to rule out demodex. Though it is fairly uncommon in adult dogs if left undiagnosed it could cause serious problems, especially since the treatment of skin ailments often involves the use of steroids. Steroids like prednisone will cause an explosion of the mites and severe worsening of the clinical signs.
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