Demodectic Mange in Dogs
What is mange?
Mange is a parasitic skin disease caused by microscopic mites. Two different mange mites cause this skin disease in dogs. One lives just under the surface of the skin (sarcoptic mange - see the handout “Sarcoptic Mange in Dogs” for more information), while the other resides in the hair follicles (demodectic mange). 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 is caused by a parasitic mite (Demodex canis or Demodex injal) that lives in the hair follicles of dogs. Under the microscope, this mite is shaped like a cigar with eight legs. Demodectic mange, sometimes just called ‘Demodex’ or ‘red mange’, is the most common form of mange in dogs.
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 cause no harm. Demodectic mange most often occurs when a dog has an immature immune system, allowing the number of skin mites to increase rapidly. This disease occurs primarily in dogs less than 12 to 18 months of age. As the dog matures, its immune system also matures.
"All normal dogs (and many humans) have a few of these mites on their skin."
Adult dogs that have the disease usually have weakened immune systems. Demodectic mange may occur in older dogs because the immune system often declines with age. Dogs who have a weakened immune system due to illness, malnutrition, or certain medications are also susceptible to 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 healthy dog to one with demodectic mange is not dangerous, as the immune system must be depressed for mange to develop.
Why doesn't the immune system mature correctly in some dogs?
The development of the immune system is under genetic or hereditary control. An affected dog often has littermates that are also affected. Owners of littermates should be alerted to watch for the development of mange in their puppies. Because the disease is due to a genetic defect, 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 may 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 referred to as localized demodectic mange. If the disease spreads to many areas of the skin, the condition is referred to as generalized demodectic mange.
"The hair loss usually begins on the face, especially around the eyes."
How is demodectic mange diagnosed?
Your veterinarian will take deep skin scrapings 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 and have not responded appropriately to treatment.
How is demodectic mange treated?
The localized form is usually treated with topical medication. The generalized form requires more aggressive treatment, usually in the form of oral or topical medications. There are several 'spot-on' topical treatments, such as moxidectin + imidacloprid (Advantage Multi®, Advocate®) and topical fluralaner (Bravecto®). These medications are used 'off-label' for the treatment of demodicosis. The term off-label describes the use of a drug for conditions other than what it was approved for.
There is an injectable form of doramectin (Dectomax®) that can also be used for the off-label treatment of demodectic mange.
Treatment for demodectic mange used to rely primarily on shampooing with special cleansing shampoos containing benzoyl peroxide, which helps to flush out and open the hair follicles prior to dipping. The dip used is a strong insecticide called amitraz. Because of the potential side effects of this treatment, and the development of newer and safer medications, this treatment is used less frequently nowadays.
Several oral medication options are also available. Ivermectins are a class of drugs that are approved for the prevention of heartworm disease in dogs and cats. Certain ivermectins are used to treat parasites in cattle. The cattle preparation has been used orally for demodectic mange in some dogs. However, ivermectin is not approved for use in treating dogs with mange, so its use to treat mite infestations in dogs is off-label.
Ivermectin is a very strong drug that can cause severe side effects, including death if it is not administered properly. It is extremely important to follow your veterinarian’s instructions and cautions carefully, as their directions may be very different from those on the label. Veterinarians do not generally recommend ivermectin for use in Collies, Shetland Sheepdogs, Australian Shepherds, Old English Sheepdogs, or any other herding breed because they are particularly sensitive to the medication.
There are several other oral medications that may be used off-label to treat Demodex mites. These include milbemycin oxime (Interceptor®), afoxolaner (NexGard®), and fluralaner (Bravecto®). Your veterinarian will help you decide which oral or topical medication is best for your dog.
"In some cases, especially dogs with generalized demodectic mange, secondary skin infections complicate the condition and require antibiotic or shampoo therapy."
In some cases, especially dogs with generalized demodectic mange, secondary skin infections complicate the condition and require antibiotic or shampoo therapy. Because dogs with skin infections often have very red, inflamed skin, demodectic mange is often called ‘red mange’. Your veterinarian will determine if your dog has a skin infection in addition to demodectic mange.
What is the prognosis for my dog?
Treatment of demodectic mange is generally successful. However, if the immune system is weakened, neither the mites nor the infection may respond to treatment. With generalized demodicosis, successful treatment may take a long time and may require regular skin scrapings to assess the progress of the treatment.
Because the immune system does not mature until 12 to 18 months of age, a dog with demodectic mange may have relapses until that age. In addition, dogs with suppressed immune systems may be susceptible to relapse. It is important to treat as soon as a relapse occurs to minimize the possibility of developing uncontrollable problems. Relapses are usually recognized three to six months after treatment is discontinued.
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