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Human scabies is caused by an infestation of the skin by the human itch mite (Sarcoptes scabiei var. hominis). The microscopic scabies mite burrows into the upper layer of the skin where it lives and lays its eggs. Scabies occurs worldwide and affects people of all races and social classes.
The microscopic scabies mite almost always is passed by direct, prolonged, skin-to-skin contact with a person who already is infested. An infested person can spread scabies even if he or she has no symptoms. Humans are the source of infestation; animals do not spread human scabies.
Scabies can be passed easily by an infested person to his or her household members and sexual partners. Scabies in adults frequently is sexually acquired.
When a person is infested with scabies mites the first time, symptoms usually do not appear for up to two months (2-6 weeks) after being infested. If a person has had scabies before, symptoms appear much sooner (1-4 days) after exposure.
The most common symptoms of scabies, itching and a skin rash, are caused by sensitization (a type of “allergic” reaction) to the proteins and feces of the parasite. Severe itching (pruritus), especially at night, is the earliest and most common symptom of scabies. A pimple-like (papular) itchy (pruritic) “scabies rash” is also common. Itching and rash may affect much of the body or be limited to common sites such as:
The head, face, neck, palms, and soles often are involved in infants and very young children, but usually not adults and older children.
Tiny burrows sometimes are seen on the skin; these are caused by the female scabies mite tunneling just beneath the surface of the skin. These burrows appear as tiny raised and crooked (serpiginous) grayish-white or skin-colored lines on the skin surface. Because mites are often few in number (only 10-15 mites per person), these burrows may be difficult to find. They are found most often in the webbing between the fingers, in the skin folds on the wrist, elbow, or knee, and on the penis, breast, or shoulder blades.
Diagnosis of a scabies infestation usually is made based upon the customary appearance and distribution of the the rash and the presence of burrows.
Whenever possible, the diagnosis of scabies should be confirmed by identifying the mite or mite eggs or fecal matter (scybala). This can be done by carefully removing the mite from the end of its burrow using the tip of a needle or by obtaining a skin scraping to examine under a microscope for mites, eggs, or mite fecal matter (scybala). However, a person can still be infested even if mites, eggs, or fecal matter cannot be found; fewer than 10-15 mites may be present on an infested person who is otherwise healthy.
Products used to kill scabies mites are called scabicides. Scabicides used to treat human scabies are available only with a doctor’s prescription.