Sarcoptic Mange
July, 2000
A few months ago, my article described ear mite infestation in
dogs. More serious diseases caused by mite infestation are the
two common types of mange -sarcoptic and demodectic.
Sarcoptic mange (scabies) is caused by the mite Sarcoptes
Scabiei. These mites cause an intensely itchy dermatitis in dogs
and can also live on the skin of cats and humans. In these
non-canine species, however,the disease is more mild. Reactions
in humans occur within 24 hours after brief direct contact and
are characterized by a red rash on the trunk and arms. This
resolves without treatment in 12 to 14 days if exposure to the
affected dog is eliminated.
The distribution pattern of the disease in dogs usually involves
the ears, elbows, legs and underside of the chest and abdomen.
The incubation period probably ranges from a few days to a few
months. As the number of mites multiplies, the itchiness becomes
more severe, and there is a point at which the untreated disease
can explode in severity. This is usually 21 to 30 days after
exposure and is probably due to the development of a
hypersensitivity, or over-reaction by the immune system. Some
dogs scratch incessantly but have few skin lesions. For
definitive diagnosis, we rely on finding mites on a skin
scraping, but many affected dogs have negative scrapings. This is
probably due to scraping areas that are inflamed by the
hypersensitivity to the mites in nearby areas. Another helpful
test for scabies is called the pinnal-pedal reflex. The edge of
the dog’s ear is rubbed or scratched and the test is
positive if the dog’s hindleg immediately and uncontrollably
tries to scratch that ear. Between 75 and 90% of dogs with
scabies have a positive pinnal-pedal reflex.
For years, the only approved method of treatment involved
applying Paramite dip weekly. As resistance seemed to develope to
this dip, others have been used, such as amitraz and lime sulphur
dips. Regardless of the topical dip that is applied or the
frequency, a 4- to 6-week course of treatment is necessary. The
most widely used, and most effective, treatment for canine
scabies is the drug ivermectin, which has been mentioned in
several SPO articles in the past. It is administered orally or by
subcutaneous injection every 2 weeks until the condition has
resolved. Most dogs require only 2 injections. The new monthly
antiparasitic medication, Revolution (selamectin), has also been
shown to effectively treat sarcoptic mange along with most other
common parasites.
Next month’s article will continue our discussion of
diseases caused by mites, as we cover demodectic mange.