Demodex – Mange in Dogs

Mange is a parasitic skin disease caused by microscopic mites. Two different mange mites cause skin disease in dogs. One lives just under the surface of the skin, while the other resides deep in the hair follicles. Although both mites share similar characteristics, there are also important differences. It is important not to confuse the two types of mange because they have different causes, treatments, and prognoses.

What causes demodectic mange?

Demodectic mange, sometimes just called “demodex” or “red mange”, is the most common form of mange in dogs. It is caused by the Demodex canis, a parasite that lives in the hair follicles of dogs. Under the microscope, this mite is shaped like a cigar with eight legs.
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All normal dogs (and many humans) have a few of these mites on their skin. As long as the body’s immune system is functioning properly, these mites live in harmony with their host and  cause no harm.

Demodectic mange most often occurs when a dog has an immature immune or a defective immune system which will allow the number of skin mites to grow rapidly. Some breeds of dogs are more prone to the disease and there may be a genetic factor for the prevalence of Demodectic mange. Because of this, the disease is found primarily in young dogs less than twelve to eighteen months of age and dogs with severe mange should not be bred. As the dog matures, its immune system also matures. Adult dogs that have the disease usually have defective immune systems. Demodectic mange may occur in older dogs because function of the immune system often declines with age. Dogs who have immune suppression due to illness or certain medications are also candidates for demodectic mange.

Is demodectic mange contagious?

No, demodectic mange is not contagious to other animals or humans. Demodex mites are transmitted to puppies from their mother during the first few days of life. Since the mite is found on virtually all dogs, exposure of a normal dog to one with demodectic mange is not dangerous.
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Why doesn’t the immune system mature correctly in some dogs?

Development of the immune system is under genetic or hereditary control. Thus, an affected dog often has littermates that are also affected. Owners of littermates should be alerted to watch for the development of the mange in their puppies. Because the disease can be due to a genetic defect of the immune system, affected dogs should not be bred, and the parents of the
affected dog should not be bred again.

What does demodectic mange do to the dog?

Surprisingly, a dog with demodectic mange usually does not itch severely, even though it loses hair in patches. The hair loss usually begins on the face, especially around the eyes. When there are only a few patches of hair loss, the condition is called localized demodectic mange. If the disease spreads to many areas of the skin, it becomes generalized demodectic mange. The mites multiply in the hair follicle which causes the hair to fall out. When the integrity of the skin is broken, then bacteria that normally resides on the skin can penetrate the broken skin and cause a secondary skin infection or a “pyoderma” . Because the immune system in these dogs in often defective, the skin infection can sometimes become severe.

How is demodectic mange diagnosed?

Your veterinarian will take deep skin scrapings and try to squeeze the mites out of the hair follicles and examine them under the microscope to diagnose this disease. The finding of larger than normal numbers of Demodex mites in skin scrapings confirms the diagnosis. Occasionally, the disease will be diagnosed by means of a
skin biopsy in dogs that have chronic skin infections that have not responded appropriately to treatment.
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What is the treatment for Demodectic mange?

The localized form is usually treated with topical medication. The generalized form requires more aggressive treatment using special follicular flushing medicated shampoos and dips, along with oral medication. Shampooing with special
cleansing shampoos containing benzoyl peroxide helps to flush out and open the hair follicles prior to dipping. In some cases, especially dogs with generalized demodectic mange, secondary skin infections complicate the condition, requiring antibiotic therapy. Dogs with skin infections often have very red, inflamed skin. This is the source of the
term “red mange.”

Are there any problems with topical treatment?

The dip commonly used for demodectic mange contains the insecticide amitraz. It must be used cautiously because it is a strong insecticide that can cause side effects, both to your dog and to you, if not used properly. Your dog may experience vomiting and sedation for twenty-four to thirty-six hours following each application. Most of these problems are self-limiting and resolve without medical intervention. If your dog reacts in this manner, you should dilute the next dip with 25% more water. Since most dogs develop tolerance to the dip as they are repeated, your dog is less likely to have side effects with each subsequent treatment. After receiving two to three dipping treatments at 2 week intervals, skin scrapings should be repeated and
examined for the presence of live mites or mite eggs. The results of these skin scrapings will determine whether further treatment is needed. Often a minimum of 6 to 8 dips is necessary to control the disease.

Is there a drug that can be given orally for demodectic mange?

Yes, under certain conditions.

Ivermectins are a class of drugs that are approved for prevention of heartworm disease in dogs and cats. Milbemycin oxime, the active ingredient of Interceptor® and Sentinel® heartworm preventives,
may be used to treat demodicosis in certain cases. Certain   ivermectins are used to treat parasites on cattle. In the past, the cattle preparation has been used orally for demodectic mange in some dogs. However, it is a very strong drug that can cause severe side-effects, including death, if it is not administered properly. It is not approved for use in dogs, so we would only consider using it as long as you are  willing to accept liability for adverse effects. Veterinarians do not generally recommend ivermectin usage in collies, Shetland sheepdogs, Australian shepherds, old English sheepdogs, or any other herding breed.

Check with your veterinarian for the recommended medicine to treat your dog.

What is the prognosis for my dog?

Treatment of demodectic mange is generally successful. However, if the immune system is defective, neither the mites nor the infection may respond to treatment. With generalized demodicosis, successful treatment may take a long time and re-occurrences can develop later in life or with stress.

Because the immune system does not mature until twelve to eighteen months of age, a dog with demodectic mange may have relapses until that age. It is important to treat as soon as a relapse occurs to minimize the possibility of developing resistant mange.

 

 

 

 

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