Scabies
What is scabies?
Scabies refers to an infestation by the itch mite, Sarcoptes scabiei. Mites are small eight-legged parasites (in contrast to insects, which have six legs). They are tiny, just 1/3 millimeter long, and burrow into the skin to produce intense itching which tends to be worse at night. The mites which cause scabies are not visible with the naked eye but can be seen with a magnifying glass or microscope.
How do you get scabies?
Scabies mites are very fastidious. They can only live off of a host body for 24 to 36 hours under most conditions. Transmission of the mites involves close person-to-person contact of the skin-to-skin variety. It is hard, if not impossible, to catch scabies by shaking hands, hanging your coat next to someone who has it, or even sharing bedclothes that had mites in them the night before. The physical contact required to contract scabies may, of course, be sexual, and scabies is more common among sexually active young people. However, other forms of physical contact, such as mothers hugging their children, is sufficient to spread the mites. Over time, close friends and relatives can contract it this way, too.
What does scabies look like, and what are the signs and symptoms of scabies?
Scabies produces small bumps and blisters in the webs between the fingers, on the wrists and the backs of the elbows, in the groin and on the knees, and on the buttocks. Men sometimes get what look like pimples on their penis. It is helpful to know that not every bump is a bug. In most cases of scabies in otherwise healthy adults, there are no more than 10 or 15 live mites even if there are hundreds of bumps and pimples.
Textbook descriptions of scabies always mention "burrows." These are tiny threadlike projections, just 2 or 3 millimeters long, which appear in the finger webs and are almost impossible to see. Often mistaken for burrows are linear scratch marks that are large and dramatic and appear in people with any itchy condition. Scratching actually destroys burrows.
What does scabies feel like?
Itching is the most common symptom of scabies. The itch of scabies is insidious and relentless. For the first weeks, the itch is subtle. It then gradually becomes more intense until, after a month or two, sleep becomes almost impossible.
The "nocturnal" nature of this itch, emphasized to every doctor and nurse in training, can be misleading. All itching is worse at night, at least in part because there is not much going on to distract people from thinking about it.
What makes the itch of scabies distinctive is its relentless quality, at least after several weeks. Other itchy conditions—eczema, hives, and so forth—tend to produce symptoms which wax and wane. These types of itch may keep people from falling asleep at night for a little while, but they rarely prevent sleep or awaken the sufferer in the middle of the night.
What is the treatment for scabies?
Curing scabies is rather easy. Steps that should be taken include:
1. Apply a mite-killer like permethrin (brand name: Elimite). These creams are applied from the neck down, left on overnight, then washed off. This application is usually repeated in seven days. An alternative treatment is 1 ounce of a 1% lotion or 30 grams of cream of lindane, applied from the neck down and washed off after approximately eight hours. Since lindane can cause seizures when it is absorbed through the skin, it should not be used if skin is significantly irritated or wet, such as with extensive skin disease, rash, or after a bath. As an additional precaution, lindane should not be used in pregnant or nursing women or children younger than 2 years old. Lindane is only recommended if patients cannot tolerate other therapies or if other therapies have not been effective.
2. An oral medication, ivermectin, is an effective scabicide that does not require messy creams to be applied. The CDC recommends taking this drug at a dosage of 200 micrograms per kilogram body weight as a single dose, followed by a repeat dose two weeks later. Although taking a drug by mouth is more convenient than application of the cream, ivermectin has a greater risk of toxic side effects than permethrin and has not been shown to be superior to permethrin in eradicating scabies.
3. Antihistamines, such as diphenhydramine (Benadryl) can be useful in helping provide relief from itching.
4. Wash linens and bedclothes in hot water. Because mites don't live long away from the body, it is not necessary to dry-clean the whole wardrobe, spray furniture and rugs, and so forth.
5. Treat sexual contacts or relevant family members (who either have either symptoms or have the kind of relationship that makes transmission likely).
Just as the itch of scabies takes a while to reach a crescendo, it takes a few days to subside after treatment. After a week or two, relief is dramatic. If that doesn't happen, the diagnosis of scabies must be questioned.
In what special situations can scabies be more easily spread?
Elderly and weakened people in nursing homes and similar institutional settings may harbor scabies without showing significant itching or visible signs. In such cases, there can be widespread epidemics among patients and health workers. Such cases are dramatic, but fortunately are uncommon.
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