What causes
demodectic mange?
Demodectic mange is caused by Demodex canis, a
parasitic mite 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.
"As long as the body's immune system is functioning properly, these mites cause no harm."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.
As a result, this disease occurs primarily in dogs less than 12 to 18 months of
age. As the dog matures, its immune system also matures.
Adult dogs that have the disease usually have weakened
immune systems. Demodectic mange may occur in older dogs because function of
the immune system often declines with age. Dogs who have a weakened immune
system due to illness 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 normal dog to one with demodectic mange is not dangerous,
as the immune system must be depressed for mange to develop.
"Demodectic mange is not contagious to other animals or humans."
Why doesn't the immune system mature correctly in some dogs?
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 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, the condition is called generalized
demodectic mange.
How is demodectic
mange diagnosed?
"Your veterinarian will take deep skin scrapings and examine them under the microscope to diagnose this disease."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 that 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 using
special 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.
There are also several 'spot on' topical treatments, such as
imidacloprid and moxidectin. 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, which can also be
used for off label treatment of demodex. Your veterinarian will
discuss the benefits and risks of these medications with you.
In some cases, especially dogs with generalized demodectic
mange, secondary skin infections complicate the condition, requiring antibiotic
therapy. Because dogs with skin infections often have very red, inflamed skin,
demodectic mange is often called ‘red mange’. Your veterinarian can help you
determine whether or not your dog has a skin infection in addition to
demodectic mange.
Are there any
problems with topical treatment?
The dip commonly used for demodectic mange contains the
insecticide amitraz. It must be used very carefully because it is a strong
insecticide that can cause serious 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 will resolve without medical intervention. If your dog reacts in this
manner, you should dilute the next dip with 25% more water. If you are using a
‘spot on’ topical treatment, you may see drooling if your dog licks the medication.
"Amitraz must be used very carefully because it is a strong insecticide that can cause serious side effects, both to your dog and to you, if not used properly."
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 seven-day
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.
I heard that there is a drug that can be given orally for
demodectic mange. Is that true?
Yes, under certain conditions.
Ivermectins are a class of drugs that are approved for
prevention of heartworm disease in dogs and cats. Certain ivermectins are used
to treat parasites on 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 sensitive to the medication.
There are a few other oral medications that may be used off
label in the treatment of the demodex mite. These include milbemycin oxime (the
active ingredient of Interceptor® and Sentinel®), afoxolaner (NexGard®), and
fluralaner (Bravecto®). Your veterinarian will help you decide which oral or
topical medication is best for your dog.
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 check the
progress of the treatment.
Following successful
treatment, is it likely to recur?
"It is important to treat as soon as a relapse occurs to minimize the possibility of developing uncontrollable problems."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 3-6 months after treatment is discontinued.
By Ernest Ward, DVM; Updated by Amy Panning, DVM
Medical Conditions, Parasites, Pet Services
https://vcahospitals.com/know-your-pet/mange-demodectic-in-dogs
Contributors: Ernest Ward, DVM; Updated by Amy Panning, DVM
© Copyright 2018 LifeLearn Inc. Used and/or modified with
permission under license.
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