What is scabies?
Scabies is 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 sensitive to their environment. 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, however, be sexual, and sexual contact is the most common form of transmission 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. School settings typically do not provide the level of close personal contact necessary for transmission of the mites.
Can you catch scabies from a dog or cat?
Dogs and cats are infected by different types of mites than those which infect humans. Scabies on dogs is called mange. When canine or feline mites land on human skin, they fail to thrive and produce only a mild itch that goes away on its own. This is unlike human scabies which gets worse and worse unless the condition is treated.
What does scabies look like? What are the signs and symptoms of scabies?
Scabies produces small red bumps and blisters and affects specific areas of the body. Scabies may involve the webs between the fingers, the wrists and the backs of the elbows, the knees, around the waist and umbilicus, the axillary folds, the areas around the nipples, the sides and backs of the feet, the genital area, and the buttocks. The bumps (medically termed papules) may contain blood crusts. It is helpful to know that not every bump is a bug. In most cases of scabies affecting 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" or "tunnels." These are tiny threadlike projections, ranging from 2 mm-15 mm long, that appear as thin gray, brown, or red lines in affected areas. The burrows can be very difficult 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. The itch is usually worse at night. For the first weeks, the itch is subtle. It then gradually becomes more intense until, after a month or two, sleep becomes almost impossible.
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 that 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 a scabies infestation?
Curing scabies is rather easy. Steps that should be taken include:
1. Apply a mite-killer like permethrin (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.
Are cases of scabies often misdiagnosed?
Scabies is very easy to misdiagnose because early subtle cases may look like small pimples or mosquito bites. Over a few weeks, however, mistakes like this become evident as patients feel worse and worse with symptoms they can't ignore.
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, uncommon.