Demodectic Mange
Teri Dickinson, DVM
Demodectic mange is a common skin disease in dogs. It is known by a
variety of names such as red mange, and is caused by a mite known as
Demodex canis. The mite is cigar shaped when viewed under a microscope,
but is not visible to the naked eye.
It is generally believed that all dogs have a small number of these
mites living in their hair follicles at all times. The mite is not
contagious from dog to dog in the usual sense, nor is it transmissible
to humans. Dogs acquire the mites during the first two to three days
of life while nursing their dams. In a large number of dogs, the mites
cause no problem, but in some individuals, skin disease does result.
Two theories1 exist about why certain dogs develop demodectic
mange, both of which deal with suppression of the immune system. While
not proven to be inherited, most researchers believe the tendency to
develop demodectic mange is hereditary, and most breeders seem to find
evidence of certain families that are more prone to the problem. One
theory regards the cause to be a defect in t- lymphocytes (a type of
white blood cell) which respond to an immunosuppressive substance produced
by the mites, resulting in a dog whose immune system cannot get rid
of the mites. The second theory holds that it is not the mites, but
a tendency to develop a bacterial infection along with the mange, which
results in the bacteria suppressing the immune system. Either way,
the result is the same, the mites and bacteria proliferate on the skin,
causing hair loss, redness, etc.
Demodectic mange is seen primarily in two forms, juvenile and adult.
Juvenile mange is further subdivided into localized and generalized
mange. The age at the onset of symptoms determines the diagnosis, with
mange beginning before about 15 months of age considered juvenile.
Localized juvenile mange is a common problem resulting in patches
of hair loss, primarily involving the face and front legs, but which
may be found anywhere on the body. The symptoms begin between three
months and a year of age, and 90%2 of the dogs cure themselves
within 4-8 weeks. The remaining dogs progress on to have generalized
mange, which is characterized by more than 10 areas of hair loss, itching,
bacterial infection and redness.
Adult onset mange is that which begins in dogs more than about two
years of age, and is not considered hereditary. Many dogs with adult
onset of mange have an underlying health problem that is suppressing
the immune system and leads to the development of the mange. A dog
with adult onset of mange should be carefully examined and have lab
work performed to rule out any underlying cause.
Diagnosis of demodectic mange involves finding a large number of mites
in affected areas. The skin is scraped with a scalpel blade and the
resulting material is examined under the microscope. A skin scraping
is a simple, inexpensive test and should be performed on every dog
with hair loss of any description in order to rule out mange as a cause.
Treatment varies with the severity of the symptoms. As localized mange
will resolve even without treatment, most veterinarians regard treatment
for localized mange as a case of treating the owner, rather than the
patient. Treatment may involve regular bathing to clear the hair follicles,
application of insecticidal ointments to the affected areas, or antibiotics.
There is no evidence that spot treatment of localized lesions will
prevent generalized mange. It is not considered advisable to treat
localized mange with amitraz (Mitoban ) dips.3 In many cases,
no treatment at all is the best treatment, with periodic visits to
the veterinarian for scrapings to determine if the numbers of mites
are increasing.
Generalized mange, either juvenile or adult onset, is a serious and
potentially life threatening disease, as unresponsive cases sometimes
require euthanasia. Treatment of generalized mange should only be undertaken
with the knowledge that it will probably take a long time, be expensive,
and may not work. Adult onset is particularly difficult to treat, due
the common presence of another underlying condition.
Treatment of generalized mange usually involves clipping the hair
to better reach the skin, bathing with antibacterial shampoos, regular
dipping with amitraz (Mitoban ) and appropriate antibiotics. Many individuals
will relapse if not treated every eight weeks or so, even after an
apparent cure. Many animals treated with amitraz develop side effects,
most notably sleepiness and depression. While frightening to owners,
these are rarely serious. Due to the presumed hereditary nature of
the disease, the American Academy of Veterinary Dermatologists recommends
the surgical neutering of any animal affected with, or recovered from,
generalized demodectic mange.
In cases which do not respond to amitraz, some success is being obtained
with milbemycin or ivermectin, oral heartworm preventives, but this
requires daily treatment, and these drugs are not approved for this
use. Some researchers feel higher concentrations of amitraz, used more
frequently, may also help, although these doses are not approved in
this country.
Thyroid hormone is not indicated unless the animal is hypothyroid,
as well as having mange. Corticosteroids (cortisone) should not be
given even if the animal is experiencing itchiness, due to the immunosuppressive
effects of these drugs.
Juvenile demodectic mange is a common problem in Italian Greyhounds.
Data from the IGCA health survey indicates some 10% of IG's have had
localized mange. Only about 5% of the affected individuals went on
to develop generalized mange, a somewhat lower figure than might be
expected. What conclusions can we draw from this information? Probably
that while localized mange is a common problem in IG puppies, most
dogs do not develop generalized mange. This would seem to indicate
that removing these animals from a breeding program would serve no
purpose, but conversely, due to the relative infrequency of generalized
mange, any affected individual should be surgically neutered.
Bibliography
1.Henfry, JI. Canine Demodicosis Update. In Practice September 1990
187-192
2. Foley, RH. Parasitic Mites of Dogs and Cats. The Compendium Vol
13, 5 p.783-786
3. Muller, GH Kirk, RW Scott, DW. Small Animal Dermatology. 1989 W.B
Saunders Co. Philadelphia PA
Copyright The Italian Greyhound
