Demodectic Mange: Symptoms and treatment
By Leslie Manis, Health/Genetics Chairman, ASTC
[Every effort has been made to ensure accuracy of information. However, this is not a substitute for prompt veterinary care. Any similarity to other publications is unintentional. Published online at Sealyhealthguard.org, 12/7/10]
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The two most common types of mange in dogs, caused by different kinds of mites, are sarcoptic and demodectic. This article will discuss demodectic mange.
The Demodex canis mite, an elongated eight-legged parasite, causes demodectic mange. The mites are not transmitted to humans. Mites are normal inhabitants of dogs' skin, often passed to puppies from their mother during nursing. In small numbers, these mites do not pose a problem. They can proliferate if the immune system is depressed. The mites live in the hair follicle, occupying the space between the hair shaft and the lining of the follicle. They cause inflammation of the hair follicle and surrounding skin, causing the hair to fall out.
As the infestation progresses, secondary bacterial or yeast infection occurs.
The immune system normally keeps the number of mites in check and most dogs never develop mange. Evidence for hereditary predisposition for generalized disease is strong. Most veterinarians do not recommend breeding dogs that have ever gotten demodectic mange.
There are two forms of the disease: localized and generalized. Localized mange mostly affects young dogs under a year old and appears as small bald patches on the face around the eyes and mouth and forelegs. The prognosis for this type of mange is good. It can be treated with topical rotenone ointment or amitraz dips.
Many times, localized mange will clear up spontaneously, but it is always advisable to seek veterinary care. [Ed.note: according to Dr. George Padgett, this form of Demodex is not considered to be hereditary.)
Generalized mange spreads over the body and can be acquired at any age. It can be serious and even life-threatening. There is rapid spreading of hairless patches throughout the coat, usually with crusting from secondary infections. The dog can also have fever, lethargy and swollen lymph nodes. This form of the disease can be extremely difficult to cure or control. It is diagnosed by skin scrapings. A veterinary evaluation should be performed to identify any underlying systemic disease. Antibiotics should be given to treat secondary infections.
Corticosteroids are not recommended, because they will further depress the immune system. The mites are killed using amitraz (Mitaban) dips every two weeks. The coat must be clipped to aid penetration, then washed with a benzoyl peroxide shampoo, such as Oxydex or Pyoben. This helps open the hair follicle and also clear up the skin infection.
The shampoo stays on 10 minutes. It can stain jewelry and clothing. The amitraz dip must be applied wearing gloves using a sponge. People taking medications such as Prozac may have an adverse reaction to the dip. The dip may cause mild sedation as a side effect. Some small dogs may experience severe sedation and require an antidote. Skin scrapings should be taken every two weeks.
The dog is considered cured if there are two consecutive negative scraping tests. (The scrapings are examined under a microscope.) The dog's immune system should be boosted by feeding a good-quality food, keeping vaccinations up-to-date and preventing other parasites, such as worms and heartworms.
There is more to learn about the hereditary and the immunological aspect of this disease. Until then, the best we can do is treat it. [Ed.Note: according to Dr. Padgett, "Generalized Demodex is considered to be inherited." Although it is not widespread in Sealyhams, it does occasionally occur, indicative of a possible genetic problem.]
Sources: The American Animal Hosp. Assoc. Encyclopedia of Dog Health & Care; merckvetmanual.com; "Canine Mange" by Dr. Kevin Byrne; marvistavet.com