Demodicosis/ Demodectic mange

What is ... ?: 

Demodex canis is a mite that is present in small numbers in the skin of most healthy dogs. Nursing puppies acquire the mite from their mothers during the first few days of life, and in most dogs there will never be any associated problems.
In some dogs however, the normal balance is disrupted due to an immune defect. The mites multiply by the thousands in the hair follicles causing inflammation, in a condition called demodicosis. Demodicosis may be localized - that is, confined to 1 or more small discrete scaly reddened areas of hair loss, most commonly on the face or front legs. This is usually seen in pups of 3 to 6 months of age, and most cases resolve spontaneously. Alternately, generalized demodicosis may develop, at anywhere from 3 to 12 months of age. This is a severe skin condition.
The defect in the cell-mediated immune system which allows the development of generalized demodicosis is believed to be inherited.

How is ... inherited?: 

unknown

What does ... mean to your dog & you?: 

It is important to note that demodicosis is not infectious, to other pets or to people. The mite is present in small numbers in the skin of healthy dogs, but the condition of demodicosis only develops in some animals, who are believed to have a defect in their immune system.
Demodicosis may be localized - a mild disorder confined to 1 or more small scaly reddened areas of hair loss, most commonly on the face or front legs. This is usually seen in pups of 3 to 6 months of age, and most cases resolve spontaneously.
Generalized demodicosis on the other hand can be one of the most severe skin diseases in dogs. It starts out with local lesions that instead of disappearing, get worse and spread, generally on the head, legs and body. Secondary infections of the hair follicles occur, and large scaly crusted patches form which may eventually cover most of the dog. The deep skin infections can be complicated by resistant bacteria.
Some dogs only develop demodicosis on the feet (demodectic pododermatitis). These lesions commonly become infected, are painful, and can be quite difficult to treat successfully.

How is ... diagnosed?: 

Your veterinarian will do a simple procedure called a skin scraping to find the mites on your dog's skin. In the shar pei, because of the thick skin, a skin biopsy is often needed to make the diagnosis. This is a simple procedure done with local anesthetic, in which your veterinarian removes a small sample of your dog's skin for examination by a veterinary pathologist.

How is ... treated?: 

Localized demodicosis: This is a mild disease that usually heals on its on within a few weeks, with or without treatment. Your veterinarian may suggest a mild parasitidal ointment or lotion to rub on the affected area. Whether or not your veterinarian recommends treatment, s/he will want to recheck your dog in about 4 weeks to make sure that the condition is not spreading.
Generalized demodicosis: In most cases this serious disease can be treated successfully. Treatment can be lengthy and expensive but the majority of dogs recover completely. In most of the rest, the disorder can be well-controlled with monthly treatment.
Most dogs recover after 4 to 8 treatments at bi-weekly intervals. Treatment for generalized demodicosis consists of clipping the dog's entire hair coat to allow better contact of the medication with the skin, removal of all crusts (which may require sedation or anesthesia depending on the extent), bathing with medicated shampoo to kill bacteria and remove debris, and application of a solution called Amitraz (Mitaban) to kill the mites. This regimen works in the majority of dogs.
Another option is  a course of oral medication, given daily for several months.
Underlying skin infections and seborrhea (scaliness) must also be treated.
For the veterinarian: In comparison to the initial scraping, a recheck skin scraping should reveal fewer mites, and fewer immature forms. If the lesions are spreading, there are more mites, and the ratio of immature forms to adults is high, than the dog should be treated for generalized demodicosis. Regional or generalized lymphadenopathy is another indicator of generalized demodicosis.
See references below for detailed discussion of treatment, including of refractory cases.

For the veterinarian: 

A skin scraping for demodectic mites should be done in all skin diseases of the feet, pyodermas, and seborrheas. Remember that an occasional adult mite seen on skin scraping is consistent with normal skin.
Over 50% of dogs with generalized demodicosis have a normocytic, normochromic, nonresponsive anemia, consistent with chronic infection. Many also have low thyroid hormone levels but they are not hypothyroid.

Breeding advice: 

Dogs that have required treatment for generalized demodicosis should not be used for breeding, and neither should their parents. Another good reason to spay females with generalized demodicosis is that during estrous, the condition worsens.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources: 

Scott, D.W., Miller, W.H., Griffin, C.E.  1995.  Muller and Kirk's Small Animal Dermatology. pp 417-432.  W.B. Saunders Co., Toronto.

Paradis, M. New approaches to the treatment of canine demodicosis in Veterinary Clinics of North America: Small Animal Practice November 1999


What breeds are affected by ... ?
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