Scabies Health Article

Definition

Scabies is a relatively contagious infection caused by a tiny mite called Sarcoptes scabiei.

Description

Scabies is caused by a tiny insect about 0.3 mm long called a mite. When a human comes in contact with the female mite, the mite burrows under the skin, laying eggs along the line of its burrow. These eggs hatch, and the resulting offspring rise to the surface of the skin, mate, and repeat the cycle either within the skin of the original host or within the skin of its next victim.

The intense itching almost always caused by scabies is due to a reaction within the skin to the feces of the mite. The first time someone is infected with scabies, he or she may not notice any itching for a number of weeks (four to six weeks). With subsequent infections, the itchiness begins within hours of picking up the first mite.

Demographics

Prevalence rates are not clear; some studies suggest that between 6 and 27 percent of the population have scabies at any one time. Scabies is more common among schoolchildren and individuals living in crowded conditions.

Causes and symptoms

Scabies is most common among people who live in overcrowded conditions and whose ability to practice good hygiene is limited. Scabies can be passed between people by close skin contact. Although the mites can only live away from human skin for about three days, sharing clothing or bedclothes can pass scabies among family members or close contacts. In May 2002, the Centers for Disease Control (CDC) included scabies in its updated guidelines for the treatment of sexually transmitted diseases.

The itching (pruritus) from scabies is worse after a hot shower and at night. Burrows are seen as winding, slightly raised gray lines along the skin. The female mite may be seen at one end of the burrow, as a tiny pearl-like bump underneath the skin. Because of the intense itching, burrows may be obscured by scratch marks left by the patient. The most common locations for burrows are the sides of the fingers, between the fingers, the top of the wrists, around the elbows and armpits, around the nipples of the breasts in women, in the genitalia of men, around the waist (beltline), and on the lower part of the buttocks. Babies may have burrows on the soles of their feet, palms of their hands, and faces.

Scratching seems to serve some purpose in scabies, as the mites are apparently often inadvertently removed. Most infestations with scabies are caused by no more than 15 mites altogether.

Infestation with huge numbers of mites (on the order of thousands to millions) occurs when an individual does not scratch or when an individual has a weakened immune system. These patients include the elderly; those who live in institutions; the mentally retarded or physically infirm; those who have other diseases which affect the amount of sensation they have in their skin (leprosy or syringomyelia); leukemia or diabetes sufferers; those taking medications which lower their immune response (cancer chemotherapy or immunosuppressant drugs given after organ transplantation); or people with other diseases which lower their immune response (such as acquired immunodeficiency syndrome or AIDS). This form of scabies, with its major infestation, is referred to as crusted scabies or Norwegian scabies. Infected patients have thickened, crusty areas all over their bodies, including over the scalp. Their skin is scaly. Their fingernails may be thickened and horny.