Canine Demodicosis

Demodicosis is a disease caused by Demodex canis, a mite that
normally lives in the hair follicles of dogs. These mites pass
from the bitch to the nursing pups at about 3 days of age. The
mite spends its entire life on the dog and it is not considered
contagious to other dogs, cats, or humans. Because of genetic
factors and/or disorders of the immune system, the number of
mites on the skin may increase dramatically and lead to the
development of lesions. The clinical signs associated with
demodicosis are highly variable and may include hair loss,
redness of the skin, and recurring bacterial skin infections.

There are two forms of demodicosis: juvenile onset and adult
onset. They are additionally classified as either “localized” or
“generalized.” The disease is generalized if two or more feet
are affected; if five or more small circular areas of hair loss,
scale, and redness are seen; or if an entire body region is
affected. Dogs with generalized demodicosis should not be bred
because the defect in the immune system that allows them to
develop the disease is believed to be inherited.

Dogs with juvenile-onset demodicosis are younger than 18 months
of age at the onset of clinical signs. The localized form of the
disease is considered benign and should not be treated because
about 80 per cent of these dogs naturally control their own mite
population within 2 to 3 months. Some develop generalized
juvenile-onset demodicosis with hair loss, crusting, and
irritation affecting the entire body. In addition to genetic and
immunologic factors, nutritional status, parasitic infections,
heat cycles, and other diseases are considered potentiating
causes.

Adult-onset generalized demodicosis (dogs older than 18 months
of age) is a serious disease because it may be an indication of
internal disease that is altering or suppressing the immune
system. Many of these dogs have received corticosteroids for a
prolonged period of time. Clinical signs are similar to those in
the juvenile-onset generalized form of demodicosis. Diagnostic
tests may be performed to investigate an underlying cause, such
as hyperadrenocorticism (excess cortisone production or
administration), hypothyroidism, systemic disease or organ
dysfunction, and cancer. Chemotherapy or other immunosuppressive
drug therapy may also lead to the development of adult-onset
generalized demodicosis.

Demodicosis is usually diagnosed by obtaining deep skin
scrapings and visualizing the mites under a microscope. The
presence of more than one adult mite or of immature forms
indicates disease. In some breeds, such as the Chinese Shar Pei,
and in dogs with chronic disease, especially of the feet, a skin
biopsy may be necessary to diagnose demodicosis. Generalized
demodicosis is a serious disease and must be treated
aggressively with drugs to control the mites and the secondary
bacterial skin infections. Treatment of generalized demodicosis
consists of identification and correction of possible underlying
diseases that have allowed the mites to proliferate as well as
specific therapy for the mites and treatment of accompanying
secondary bacterial infections. Most treatments for demodicosis
require months of intensive therapy.

It is not unusual for your veterinarian to prescribe an extended
course of oral antibiotics to treat the deep bacterial skin
infections that frequently accompany demodicosis. Other
treatments are available for demodicosis, but amitraz (Mitaban)
is the only treatment for demodicosis that is approved by the
U.S. Food and Drug Administration. In any treatment plan for
demodicosis, corticosteroids (topical or systemic) are
contraindicated.

Your veterinarian may recommend that Mitaban dips initially be
performed in the veterinary hospital by qualified personnel to
ensure that the treatment is performed correctly as well as to
observe for side effects. Medium-haired and long-haired dogs
should be clipped every 3 to 4 weeks to facilitate adequate
penetration of the Mitaban dip. Dogs should be bathed with a
benzoyl peroxide shampoo before each dip. The dip is mixed with
water according to the instructions given by your veterinarian
in a well-ventilated room or outdoors. Rubber gloves should be
worn and, using a sponge, the mixture applied thoroughly to
saturate the skin. The dip should be applied with the dog
standing in a washtub as the dip runoff is reapplied with a
sponge for a full 15 minutes. It is important to treat the
facial area, ears, and feet as these regions are commonly
affected by demodicosis. Dogs that have demodicosis affecting
the feet should stand in the dip preparation for a minimum of 15
minutes. The dip should not be rinsed off. Allow the dog to air
dry. Your dog should not be allowed to become wet (including the
feet) between Mitaban treatments, as this washes off the
medication. This procedure should be repeated as directed by
your veterinarian. A new mixture must be prepared for each
treatment because the drug is unstable when exposed to light and
air; for the same reason, any remaining dip should be discarded.
The side effects of Mitaban include lethargy, skin irritation,
itchiness, loss of appetite, and occasional vomiting or
diarrhea. Side effects are more commonly seen in small dogs,
especially the toy breeds. If side effects are observed, your
veterinarian should be notified.

Other drugs can help in the treatment of demodicosis. These
systemic drugs are ivermectin and milbemycin. If your dog has
not received heartworm preventive on a regular basis, your
veterinarian needs to perform a blood test for heartworm disease
before administration of either of these drugs. The side effects
of ivermectin and milbemycin include decreased appetite,
lethargy, weakness, dilated pupils, tremors, vomiting, coma, and
death. Usually the more serious side effects occur with
ivermectin, but they may also occur with milbemycin. The side
effects are rare and usually resolve with discontinuation of the
drug. Collies, Shetland sheepdogs, Old English sheepdogs,
Australian shepherds, border collies, or their crosses should
not be treated with ivermectin.

Your dog needs to be evaluated by your veterinarian every 4 to 8
weeks. Skin scrapings are obtained at each visit and treatment
usually continues until two or three consecutive skin scrapings
have been negative. Treatment is discontinued at this time, and
your dog is reevaluated every 3 months for 1 year. Your dog is
not considered “cured” until 1 year has passed without
visualization of mites on skin scrapings. A small percentage of
dogs have chronic demodicosis and may require lifelong therapy.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.