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Scabies is a contagious skin infection that occurs among humans and animals. It is caused by a tiny and usually not directly visible parasite—the mite Sarcoptes scabiei—which burrows under the host's skin, causing intense allergic itching. The word scabies is derived from the Latin word scabere, which means scratch. Colloquially it is the disease known as the seven year itch. The infection in animals (caused by different but related mite species) is called sarcoptic mange.

The disease in humans may be transmitted from objects or bedding (like matresses,etc.), but is most often transmitted by direct skin-to-skin contact, with prolonged contact being more efficient. Initial infections of scabies require four to six weeks to become symptomatic. However, persons who have recently been cured of the disease, upon re-infection, may manifest symptoms within as little as 24 hours. Because the symptoms are allergic, their delay in onset is often mirrored by a significant delay in relief after the parasites have been eradicated.

Scabies mites prefer thin hairless skin, and for this reason concentrate on intertriginous parts of the body below the neck, (between fingers and in skin folds), avoiding callused areas. Infants may be infected over any part of the body, as may also immunosuppressed persons. Otherwise healthy persons with good hygeine may be infected with only an average of 11 mites. Crusted scabies, formerly known as "Norwegian scabies," is a more severe form of the infection often associated with immunosuppressed hosts. In crusted scabies, the mites, numbering thousands in such cases, cause scaly rashes and thick crusts of skin.

In both humans and animals, the disease can be effectively treated with a number of medications. Permethrin cream is the most effective, but expensive compared to other treatments. Crotamiton is less effective, but also nontoxic and soothing, allowing it to be used more often. Ivermectin is also used orally and topically, subject to restrictions involving treatment toxicity differences between hosts. Treatment with lindane preparations have fallen out of favor due to high toxicity and parasite resistance. In order to prevent re-infection, the host's contacts are also often treated.


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