(ALSO CALLED “SCABIES”)
THE ORGANISM AND HOW IT LIVES
Sarcoptic mange is the name for the skin disease caused by infection with theSarcoptes 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. 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, 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. 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. 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.
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 2-4 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.
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.
While sarcoptic mange is difficult to diagnose definitively, it is fairly easy to treat and a number of choices are available.
Anti-bacterial or anti-itch shampoos preceed one of several anti-mite dips. 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.
This is one of the most effective treatments against Sarcoptes scabeiyet 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. For more information on ivermectin use click here.