What are scabies?
The human scabies mite Sarcoptes scabiei, a small arachnid, approximately 0.4 millimeter long, produces intense pruritus (itching) and a red rash. Though scabies is most commonly noted on the fingers and hands, almost any skin surface can be affected. After fertilization, the female mite burrows into the upper layer of the host’s skin and deposits several eggs. Upon hatching, the young migrate to the surface, where they mature; this life cycle lasts three to four weeks. In most cases, an affected human host will have an average of eleven adult females. The elderly and immunocompromised patients are susceptible to a more severe, widespread variant called Norwegian scabies. In cases of Norwegian scabies, a human host may carry more than two million adult females.
A patient with scabies generally complains of severe itching, and the skin may be inflamed from scratching. Examination with a magnifying lens reveals characteristic burrows several millimeters in length, especially in the spaces between the fingers. A skin scraping aids in the diagnosis, producing a specimen for microscopic viewing which reveals the adult mite, eggs, or feces.
The treatment of scabies is straightforward. Clothing and bed linen should be washed in hot water. Shoes or other articles that cannot be washed may be sealed in a plastic bag for a week; this kills the mites, which need a human host to survive for more than a few days. Patients are treated with a 5 percent preparation of permethrin applied from head to foot (sparing the mouth and eyes) and left on overnight. An alternative treatment is lindane, which is less commonly used because of the risk of nerve toxicity in children. With either treatment, the medication is rinsed off in the morning shower. A single dose of oral ivermectin may be used alone or in combination with topical agents to treat difficult cases. Rapid diagnosis and treatment decrease the chance of the mites spreading to other individuals.
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