Section 18. Skin Disorders

Chapter 210. Parasitic Skin Infections

Topics: Introduction | Scabies | Lice Infestation | Creeping Eruption

Scabies

Scabies is a mite infestation that produces tiny reddish bumps and severe itching.

Scabies is caused by the itch mite Sarcoptes scabiei. The infestation spreads easily from person to person on physical contact, often spreading through an entire household. In rare cases, mites can be spread on clothing, bedding, and other shared objects, but their survival is brief, and normal laundering destroys them.

The female itch mite tunnels in the topmost layer of the skin and deposits her eggs in burrows. Young mites (larvae) then hatch in a few days. The infestation causes intense itching, probably from an allergic reaction to the mites.

Symptoms and Diagnosis

The hallmark of scabies is intense itching, which is usually worse at night. The burrows of the mites are often visible as very thin lines up to ½ inch long, sometimes with a tiny bump at one end. Sometimes, only tiny bumps are seen, many of which are scratched open because of the itching. The burrows can be anywhere on the body except the face. Common sites are the webs between the fingers and toes, the wrists, ankles, buttocks, and, in males, the genitals. Over time, the burrows may become difficult to see because they are obscured by inflammation induced by scratching. People with a weakened immune system may develop severe infestations, which produce large areas of thickened, crusted skin.

Usually, itching and the appearance of burrows are all that are needed to make a diagnosis of scabies. However, a doctor can confirm the diagnosis by taking a scraping from the bumps or burrows and looking at it under a microscope to confirm the presence of mites, eggs, or mite feces.

Treatment

Scabies can be cured by applying a cream containing 5% permethrin, which is left on the skin overnight and then washed off. Although only one treatment is usually needed, some people require a second treatment a week later. Ivermectin taken by mouth in two doses given a week apart also is effective and is especially helpful for severe infestations in people with a weakened immune system.

Even after successful treatment, itching may persist for up to 2 weeks because of a continued allergic reaction to the mite bodies, which remain in the skin for a while. The itching can be treated with mild corticosteroid cream and antihistamines taken by mouth (see Section 18, Chapter 203). Occasionally, the skin irritation and deep scratches lead to a bacterial infection, which may require antibiotics given by mouth.

Family members and people who have had close physical contact, such as sexual contact, with a person with scabies should be treated as well. Clothing and bedding used during the preceding few days should be washed in hot water and dried in a hot dryer or can be dry cleaned.