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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 3-4 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.
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 2-4 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.
ALL DOGS IN A HOUSEHOLD WHERE
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 (ie 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 PRESENT IN THE HOME, |
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