Sarcoptic Mange

(ALSO CALLED SCABIES)

THE ORGANISM AND HOW IT LIVES
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 to 4 weeks in the host’s skin. After mating, the female burrows into the skin depositing 3 to 4 eggs in the tunnel behind her. The eggs hatch in 3 to 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.
Sarcoptes Scabei: Female sarcoptes mite burrowing in the skin and leaving a trail of eggs behind her. Her presence generates an inflamatory response in the skin similar to an allergic response.

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, scaley 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.

Dog with dematitis problem typical of sacrcoptic mange. Note: Many dogs do not develop the classical ear margin crusts until later in the disease.
As the infection progresses, eventually most of the dog's body will be involved. Classically, though, the picture begins 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 "maybe mange" test is frequently performed. This consists simply of treating for sarcoptic mange and observing for resolution of the signs within 2 to 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.

IVERMECTIN- This is one of the most effective treatments against Sarcoptes scabei yet it is off-label as far as the FDA is concerned. Typically an injection is given either weekly or every two weeks for a total of 1 to 4 doses. In most cases this treatment is safe and effective but some individuals have a mutation that makes ivermectin very toxic at the doses used to kill mites. These individuals are usually of the Collie family but other individuals may be affected.
 
There is now a DNA test that can determine if any dog has the mutation that makes ivermectin use dangerous. This test is done at Washington State University. For more information, visit www.vetmed.wsu.edu/vcpl.

SELAMECTIN (REVOLUTION®) - Selamectin is an ivermectin derivative recently marketed for the control of fleas, roundworms, hookworms, ticks, ear mites and sarcoptic mange mites. Normal monthly use of this product should prevent a sarcoptic mange problem but to clear an actual infection studies show an extra dose is usually needed after 2 weeks for reliable results. This product is probably the best choice for Collie or Australian shepherd breeds.

ALL DOGS IN A HOUSEHOLD WHERE
SARCOPTIC MANGE HAS BEEN DIAGNOSED
SHOULD BE TREATED.

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

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).

IF A SARCOPTIC MANGE ANIMAL IS IN THE HOME, IT IS A GOOD IDEA TO WASH ANY BEDDING IN THE WASHING MACHINE (OR REPLACE WITH NEW BEDDING), AND WASH ANY COLLARS OR HARNESSES.