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Demodectic Mange - by
Frances Smith, DVM
Posted September 2001
Demodectic mange, often called red mange, is a skin disease of dogs that
is caused by a microscopic mite called Demodex canis. This mite is
present in small numbers on most dogs. How do dogs get them in the first
place, you ask? Puppies get them from their mothers in the first few
days of life. The real problem comes when these mites reproduce and
dramatically grow in numbers causing disease in the skin. No one really
knows exactly why this happens in some dogs but not in others. Stress
seems to be a big factor and since some families of dogs have
demodicosis, it is likely that these dogs have a genetically inherited
defect of the immune system.
THREE TYPES
There are three types of demodicosis: localized, generalized, and
pododermatitis.
Localized demodicosis usually causes small patches of red scaly skin and
hair loss. This occurs most commonly on the face, especially near the
eyes and edges of the mouth, and on the front legs, but can occur
anywhere on the body. These lesions are not itchy unless they get
infected and are seen primarily in puppies about 3-6 months old. Ninety
percent of these puppies clear spontaneously (with no treatment) in 6-12
weeks. If a secondary bacterial infection is present, a benzoyl peroxide
gel may be used to help kill the bacteria and flush the hair follicles.
If your puppy has localized demodicosis, you will need to take it back
to the vet in 3-4 weeks for a recheck. This is to make sure the
condition is improving and not becoming generalized. About 10% of
localized demodicosis becomes generalized, but there is no evidence that
aggressive treatment of localized lesions will prevent the development
of the generalized form. In some animals this just seems to be
genetically programmed.
Generalized demodicosis is just what it sounds like – the mites are
everywhere! The skin may be very red, lose lots of hair, have crusts and
sores, dark pigment, and deep infections. The animal may be seriously
ill, feverish, and not eating. There are two groups of this type:
juvenile onset and adult onset. Juvenile onset usually begins when the
pup is between 3 and 12 months old and 30-50% of these may recover
spontaneously, with or without treatment. Adult onset occurs mostly in
dogs over 2 years old. Often it is associated with other diseases such
as heartworms, endocrine diseases (like Cushings disease or
hypothyroidism), cancer, or corticosteroid treatment (often used in
treating allergic skin disease). There is an inherited tendency to have
generalized demodicosis so affected animals should never be bred. In
some animals, especially those with the adult onset variety, this
disease can be difficult to cure, but can usually be controlled.
Demodectic pododermatitis is limited to the paws. These dogs have
swollen red feet with pyogenic (pus) lesions between the toes and
sometimes in the nail bed. This is extremely difficult to treat.
Pododermatitis is often chronic and quite resistant to many therapies.
It is seen more commonly in adult animals.
DIAGNOSIS
Deep skin scrapings diagnose demodicosis. The veterinarian will pinch up
a small amount of affected skin and scrape until there is a little
bleeding. This is necessary because these mites live in the hair
follicles and, if the follicles rupture, in the dermis (a deeper layer
of the skin). This material will be spread on to a slide and examined
under the microscope. If the mites are present there may be adult mites,
eggs, or various stages of immature mites. There will be a great number
of each of these life stages in very active infections. Sometimes dogs
with very thick skin, such as Shar Peis, require a skin biopsy to make
the diagnosis. Several areas may be scraped, even normal looking areas,
to help determine if the problem is localized or generalized. This is
especially important with breeds that tend not to lose much hair like
Shih Tzus and Lhasas.
TREATMENT
Localized demodicosis is generally not treated because, as stated
earlier, 90% of these cases resolve spontaneously. If a topical
medication to kill mites is used, the lesions will probably look worse
before they look better. Rubbing the ointment into the skin can break
off fragile hair at the edges and make the hairless area look bigger.
Dipping with Mitaban is NOT recommended in the treatment of localized
demodicosis.
Generalized demodicosis is treated by eliminating bacterial infection
with antibiotics, bathing in antibacterial and keratolytic shampoos (benzoyl
peroxide shampoos are great) to flush follicles and remove crusts, and
dipping in Mitaban. Mitaban, or amitraz, is currently the only FDA
approved treatment for generalized demodicosis. It is a monoamine
oxidase inhibitor and is acaricidal (kills mites) by an unknown
mechanism. Longhaired dogs often need to have their entire body clipped
so the dip will get to the skin. The size and age of the dog and the
severity of the problem determine the strength and frequency of the
dips. This treatment can take several months and must continue until
several negative skin scrapings are seen. Affected dogs should not be
stressed during treatment. Females should be spayed as soon as they are
stable because the stress of heat may cause a relapse. Sometimes the
stress of anesthesia and surgery can also cause a relapse. As with most
treatments, there are possible side effects. The most common one is
sedation that can last as long as 72 hours. Other possible reactions
include itching, ataxia (unsteady gait), hyperexcitability, pain,
hyperglycemia, red eyes, appetite stimulation, drinking a lot of water,
urinating a lot, vomiting, diarrhea, swelling, redness and bleeding from
the feet, and seizures. A few deaths have been reported. There is a
reversal agent called Yohimbine that can be given before dips and every
3 hours after as needed if the reactions are severe. Mitaban dips are
often done in the veterinary hospital so that the animal can be watched
for adverse reactions and precautions can be taken to keep the people
dipping the dog safe.
People with asthma, diabetes mellitus, Parkinson’s disease, and those
taking selected serotonin reuptake inhibitors (SSRI’s such as Prozac)
should NOT administer these dips. The SSRI’s can cause a serious and
possibly life threatening HUMAN reaction if the person taking the SSRI
has skin contact with liquid Mitaban..
Other treatments that may be tried if mitaban fails are daily oral
milbemycin (Interceptor) or ivermectin. These are not FDA approved
treatments for demodicosis. Ivermectin should never be used in collies,
Shetland Sheepdogs, Old English Sheepdogs, Australian Shepherds and
sometimes other herding dogs. Vets have a saying regarding ivermectin:
White feet? Don’t treat!
One old home remedy that still occasionally occurs is dipping in motor
oil, sometimes with sulfur. DO NOT PUT MOTOR OIL, burnt or otherwise, ON
A DOG! It can cause rashes or even destroy skin. If ingested or absorbed
it can cause vomiting (which can lead to aspiration pneumonia if the oil
is inhaled), kidney and liver damage. The reason some of these dogs get
better is because they would anyway! Remember, 90% of localized and
30-50% of generalized demodicosis get better with no treatment.
SO, WHAT DO YOU DO?
If you see a red crusty place on your puppy, have it checked. If the vet
determines it is localized demodicosis, watch it closely. It should not
get worse and hair will grow back in 6-12 weeks. Feed your pup good
quality food, continue vaccinations, keep giving heartworm prevention,
and treat any parasites such as intestinal worms or ticks and fleas.
If you have a dog with several crusty red lesions that progress fairly
quickly and cover more of the body, have it checked immediately. If it
does have generalized demodicosis, treat as your vet recommends and keep
him or her as healthy as you can otherwise. Generalized demodicosis can
be quite challenging to treat and may turn into a chronic problem
requiring long-term therapy. It does take time and money, so the owner
of a dog with generalized demodicosis should be prepared to invest both.
Many dogs used to die or be euthanized because of demodectic mange.
Thanks to today’s drugs and treatment protocols most dogs can be cured
or at least controlled.
Please note: The information provided here is meant to supplement that
provided by your veterinarian. Nothing can replace a complete history
and physical examination performed by your veterinarian.
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