Scabies, also known as sarcoptic itch and acariasis, is the highly contagious infestation with Sarcoptes scabiei, a tiny, whitish-brown, eight-legged mite that burrows into the skin to lay its eggs. Burrowing, egg laying, and feces deposition cause severe skin irritation, eruption, and itchy rash.
Scabies mites live for about 30 days, during which time the female mite can lay two or three eggs a day. Eggs hatch quickly and the nits grow to maturity in about 10 days, continuing the cycle of infestation.
Incidence and Prevalence of Scabies
An estimated 300 million cases of scabies occur worldwide each year. It is most prevalent among people in close contact with others, especially children, mothers, and the elderly in nursing homes. Children under 2 years of age are at highest risk.
Causes of Scabies
The mite that causes scabies is capable of moving about 1 inch per minute. Scabies infestations are spread through both casual and sexual contact, when the mite migrates from one host to another. One can be infected by contact with contaminated clothing, towels, upholstery, or bedding.
Signs and Symptoms of Scabies
The scabies itch is often severe and usually worse at night and while bathing. Visible symptoms include rash and bumps between the fingers; inside the wrists, elbows, or knees; in the skin creases of the buttocks and groin; around the navel and nipples (especially in women); on the feet; and on external genitalia.
The bumps contain nests for hatching and growing mites. They can become inflamed, crusty, and hard, and can persist for weeks after treatment. The burrows may appear as short, zigzag, grayish lines under the skin. Scabies is a local infection with no known systemic complications. The itching and rash will intensify and spread without treatment. Scratching often produces secondary bacterial infection, pus-filled lesions, and cracks in the skin.
Diagnosis is made by physical examination. Scabies lesions can be scraped to obtain a sample of tissue, which is mixed with potassium hydroxide (KOH) and examined under a microscope for eggs, feces, and mites. This test confirms the diagnosis and rules out other skin diseases that cause itching.
Treatment for Scabies
Self-treatment with over-the-counter cortisone creams is discouraged. Topical prescription medications are used to treat scabies infestations, including lotions that contain crotamiton, which are applied from the neck down. Lindane is a pesticide that is associated with neurological damage, poisoning, cancer, and environmental contamination. Its use to treat scabies in adults is controversial and it is no longer used in children.
Coating the body with a mixture of petroleum jelly and 5% sulfur for 3 consecutive nights has also proven beneficial. Itching caused by the absorption of mites and their feces into the body can last for weeks, leading people to believe they are still infected.
The lesions caused by scabies should be kept clean to prevent infection. Physicians may advise wearing cotton gloves during and after treatment to prevent breaking the skin by scratching, which can cause secondary infection.
The parasites cannot survive away from the body for more than a few days, so contaminated clothing and bedding can be sanitized by thorough washing in hot water and storing for 1 or 2 weeks.