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 affects everyone regardless of age, gender, race, social class, or personal-hygiene habits. 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, are sufficient to spread the mites.
How Long Does Scabies Last?
The mite cannot live more than three days without a human host, but it can survive up to a month when living on a human. The mite also lays eggs in human skin, which hatch and grow into adult mites. This means that symptoms of the condition can last for months or even years.
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 Are the Signs and Symptoms of Scabies?
Scabies produce small red bumps and blisters and affect specific areas of the body. Scabies may involve the webs between the fingers, the wrists and the backs of the elbows, the knees, areas 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."
What Do Scabies Look Like?
Textbook descriptions of scabies always mention "burrows" or "tunnels." These are tiny thread-like projections, ranging from 2 mm-15 mm long, which 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 as shown on this slide. The scaly patch at the left is due to scratching of the original papule. The mite traveled from there to the upper right, where it can be seen as a dark spot at the end of the burrow.
What Does a Scabies Infection 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.
How is scabies tested and diagnosed?
Most cases of scabies can be diagnosed by describing the symptoms to the doctor and by examination of the skin. There is no blood test for scabies.
- Sometimes, the doctor will do a skin scraping to make or confirm the diagnosis. This is performed by placing a drop of oil or saline on top of an affected area. Then using a scalpel, the area is scraped, and the material that was collected is placed on a slide to examine under a microscope. The doctor will look for the mite or its eggs.
- The doctor may perform a felt-tip-marker test by drawing a washable felt-tip marker across the rash and then wiping it off with alcohol. This may help to identify a burrow because the ink penetrates deep into the skin.
- Often, there are a few mites that can be hard to find. Therefore, even if the scrapings are negative, the doctor may still recommend treatment if he or she is very suspicious that scabies is present.
Scabies Treatment: Cream Applications
Apply a mite-killer like permethrin (Elimite). These creams are applied from the neck down, left on overnight, and 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 of age. Lindane is only recommended if patients cannot tolerate other therapies or if other therapies have not been effective.
Ivermectin, is an oral antiparasitic medication that has also been shown to be an effective scabicide, although it is not FDA-approved for this use. It is taken 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. It is typically used only when topical medications have failed or cannot be tolerated.
Antihistamines, such as diphenhydramine (Benadryl), can be useful in helping provide relief from itching.
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.
- Treat sexual contacts or relevant family members (who either have symptoms or have the kind of relationship that makes transmission likely).
- Cut your nails, and clean under them thoroughly to remove any mites or eggs that may be present.
- Thoroughly vacuum your rugs, furniture, bedding, and car interior and throw the vacuum-cleaner bag away when finished.
- Try to avoid scratching. Keep any open sores clean.
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.
Scabies (right) is very easy to misdiagnose because early subtle cases may look like small pimples (left) or mosquito bites (center). Over a few weeks, however, mistakes like this become evident as patients feel worse and worse with symptoms they can't ignore.
The elderly and people with weakened immune systems 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-care workers. Such cases are dramatic but, fortunately, uncommon.
The term "Norwegian scabies" refers to a particularly severe form of scabies that is also known as crusted scabies. Crusted scabies has been called Norwegian scabies because the condition was first described in Norway in the mid-19th century.
Norwegian scabies is different from traditional scabies as there seems to be a problem with the immune response to the mites, allowing for the infestation of an individual with hundreds of thousands of the mites. Crusted scabies almost always affects people with a compromised immune system and is observed most frequently in the elderly, mentally or physically disabled, and in patients with AIDS, lymphoma, or other conditions that decrease the effectiveness of the immune response. The lesions of this distinctive form of scabies are extensive and may spread all over the body. The elbows, knees, palms, scalp, and soles of the feet are most commonly the original sites of involvement, and the scaly areas eventually take on a wart-like appearance. The fingernails can be thickened and discolored. Interestingly, itching may be minimal or absent in this form of scabies.
