Sarcoptic mange
(ALSO
CALLED "SCABIES")
THE ORGANISM AND HOW IT LIVES
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Sarcoptic mange is the name for the skin
disease caused by infection with the Sarcoptes
scabei mite. Mites are not insects; instead they
are more closely related to spiders. They are microscopic and cannot be
seen with the naked eye.
Adult Sarcoptes scabei
mites live 3-4 weeks in the host’s skin. After mating, the female burrows into
the skin depositing 3-4 eggs in the tunnel behind her. Her presence generates an inflammatory response in the skin similar to
an allergic response. The eggs hatch in 3-10 days producing a larva
which, in turn, moves about on the skin surface eventually molting into a
"nymphal" stage and finally into an adult.
The adults move on the surface of the skin where they mate and the cycle begins
again with the female burrowing and laying eggs.
APPEARANCE OF THE DISEASE
The motion of the mite in and on the skin
is extremely itchy. Further, the presence of mites and their eggs
generates a massive allergic response in the skin which is even more itchy.
Mites prefer hairless skin thus leaving
the ear flaps, elbows and abdomen at highest risk for the red, scaly itchy skin
that characterizes sarcoptic mange. It should be noted that this pattern of
itching is similar to that found with airborne
allergies (atopy) as well
as with food
allergies. Frequently, before attempting
to sort out allergies, a veterinarian will simply treat a patient for sarcoptic
mange as a precaution. It is very easy to be led down the wrong path (pursuing
allergy aggressively) if one considers sarcoptic mange an unusual or unlikely
possibility.
As the infection progresses, eventually
most of the dog's body will be involved. Typically, we see the first signs on
the ears (especially the ear margins), the elbows, and abdomen.
The term "Scabies" refers to mite infestations by either Sarcoptes scabei or
other mite species closely related to Sarcoptes scabei. While Sarcoptes
scabei can infect humans and cats, it tends not
to persist on these hosts. When people (including some veterinarians) refer to
"sarcoptic mange" or "scabies" in the cat, they are usually
referring to infection by Notoedres cati, a mite closely related to Sarcoptes
scabei. In these feline cases, it would be
more correct to refer to "Notoedric mange,"
though the treatment for both mites is the same. Notoedric
mange, in cats, generally produces facial itching and scabbing.
DIAGNOSIS
When an animal with sarcoptic mange
scratches itself, it breaks open the tunnels that the mites have burrowed into
and the mites are killed (though the itch persists due to toxins in the skin).
The result is that the mites can be very difficult to confirm by skin scraping
tests. (Probably mites are confirmed in 50% or fewer of sarcoptic mange
cases).
Since negative test results do not rule
out mite infection, a "May be Mange" test is frequently performed.
This consists simply of treating for sarcoptic mange and observing for
resolution of the signs within 2-4 weeks.
Of course, if mite presence is confirmed
by skin scraping, then one knows immediately the cause of the itching and need
not be concerned about allergy possibilities or other diseases and the
condition can be addressed with confidence.
BIOPSY - Mange mites are rarely seen on a skin biopsy sample,
though, if the sample is read out by a pathologist who specializes in skin, the
type of inflammation seen in the sample can be highly suggestive of sarcoptic
mange. This is an example of a skin disease where it makes a difference whether
the pathologist reading the sample specializes in reading skin samples.
TREATMENT
While sarcoptic mange is difficult to
diagnose definitively, it is fairly easy to treat and a number of choices are
available.
DIPPING – A good bath with an anti-bacterial or anti-itch shampoo
should be given before one of several anti-mite dips is applied. Paramite dip (an organophosphate), Mitaban
dip (Amitraz), and Lime-Sulfur dips given weekly are
usually effective. Disease typically resolves within one month. Dips are often
used in combination with one of the other treatments listed below.
IVERMECTIN - This is one of the most effective
treatments against Sarcoptes scabei yet is is off-label as
far as the FDA is concerned. There are several protocols due to the very long
activity of this drug in the body. Typically an injection is given either
weekly or every two weeks in 1-4 doses. In most cases this treatment is safe
and effective but some individuals have a mutation which makes ivermectin very toxic at the doses used to kill mites.
These individuals are usually of the Collie family: Collies, Shetland
Sheepdogs, and Australian Shepherds are classically affected. There is now a
test that can determine if any dog has the mutation that makes ivermectin use dangerous.
MILBEMYCIN OXIME (INTERCEPTOR®
OR SENTINEL®)
- Milbemycin Oxime is approved for heartworm prevention as a monthly oral
treatment. Happily, it also has activity against sarcoptic mange and several
protocols of varying success have been recommended by different dermatologists.
This is another medication that one might find recommended.
For more information from the
manufacturer, visit their page for Interceptor:
http://www.petwellness.com/dog_inter_home.asp
or their page for Sentinel:
http://www.petwellness.com/dog_sent_home.asp
Another new choice for
treatment is Advantage Multi. As with Sentinel it is also a heartworm
preventative, so cannot be used on patients without a current negative
heartworm test. Advantage Multi is a topical treatment that is usually applied
monthly to prevent heartworms and fleas, the vet may prescribe it to be applied
more frequently to treat sarcoptic mange.
HOW THE INFECTION IS SPREAD
Sarcoptic mange mites are usually spread
by direct contact from host to host. While mites can live off of a host for
days to weeks depending on their life stage, they are only infective for 36
hours which means that environmental decontamination is generally not
necessary.
Mite infections on humans are
self-limiting (i.e. they go away on their own) as the mite is not able to
complete its life cycle on the "wrong" host. The condition is
extremely itchy, though, while it lasts. The mites are most active where skin
is warm (in bed and where clothing is snug).
Sarcoptic mange is extremely contagious!
ALL DOGS
IN A HOUSEHOLD WHERE
SARCOPTIC MANGE HAS BEEN DIAGNOSED
SHOULD BE TREATED.
IT IS A GOOD IDEA TO WASH ANY BEDDING IN
THE WASHING MACHINE (OR REPLACE WITH NEW BEDDING),
AND WASH ANY COLLARS OR HARNESSES.