John R. Tkach, M.D.
300 North Willson, Suite 203B
Bozeman, MT 59715
(406) 587-5442

Scabies

Patient Information Sheet

Scabies is an infestation of the skin by the microscopic eight-legged mite Sarcoptes scabiei. It produces intense itching that often wakes people up at night. Itchy 1 mm papules and vesicles appear commonly on the palms, sides of the fingers, nipples, and especially the genitals. The vesicles can also occur on any other part of the skin. It should not occur above the neck. 60% of the mites occur on the hands.

There is a rare variant called Norwegian scabies that affects the head and scalp producing thick scaly crust. It looks uncharacteristic of scabies and can be misdiagnosed. It usually occurs in people with immune deficiency such as AIDS.

Sometimes people suffer emotionally unnecessarily. Look, this is a treatable disease that should leave no long lasting results. But the idea of hundreds of little bugs crawling on the skin is distressing to some people. That is a misunderstanding. First, you cannot see the mites. That requires a microscope. Secondly, the distance the mite crawls in its lifetime is about 1-2 mm. They are not crawling around all over you. It's more that they are sitting there. You spread them by scratching. The mites rely on scratching. That's why the hands are affected.

Contracting scabies usually requires prolonged skin-to-skin contact with an infested person. Sharing a bed, holding hands, touching hands as in handshakes, and sexual contact are common ways people get scabies. I had a patient who got scabies on her hands working as a cashier in a grocery store and passing money back and forth by hand to customers.

It is also possible to get scabies from infested bed linens, sleeping bags and sharing towels. In World War II, large numbers of people were sleeping in bunk beds in subway stations. A study was done on infested sheets such that the sheets were not changed and multiple people used the beds in succession. They found that 1 person in 300 got scabies this way. But I do see this here in Bozeman usually when an out of town visitor comes and shares a sleeping bag or towels.

The mites tend to be in the roof of the vesicles. The female mite crawls from the skin of person to another person. After about 53 minutes of skin-to-skin contact, the mite crawls onto the skin of the second person. She burrows into the thin outer layer of dead skin and lays her eggs. After an incubation period of about 1 week, there may be 5 to 10 females laying eggs. In two months there are 50 mites. In three months there are 100 to 200 mites.

The infestation is limited to the locally affected area that itches. They do not crawl into you mouth or get inside your body into your blood or internal organs. The infestation is strictly limited to the outer layer of dead skin, which is thinner than a piece of paper.

The hallmark symptom of scabies is itching. But, it is not because the mites are biting or stinging you. What happens is that about a month after initial contact, your immune system becomes allergic to the foreign proteins of the mites kind of like getting allergic to poison ivy. In fact, scabies can look a little like poison ivy rash.

The point at which you start to notice itching is a month after you contracted scabies. So, think back to what was going on then. Also, check family members. It is likely others have become infested and you should all be treated at the same time. Think back to those you have contacted. Consider warning them that if they get itchy, they should see their doctor. Scabies can spread around the community, especially nursing homes, hospitals, and institutions.

The best confirmatory lab study is the KOH prep, which I can perform in my office. Often the diagnosis is so obvious, a KOH prep is not needed. But sometimes scabies is puzzling and the KOH prep helps. I scrape the vesicle roof off and put it on a microscope slide and look at it under the microscope. It is a simple but profound study. I have had to scrape as many as 20 vesicles to find one that is positive. Atopic dermatitis can look like scabies, but the KOH prep is negative.

Scabies in History

Historically, scabies is an interesting disease that has affected thousands of people in large epidemics. It is believed that the Grand Army of Napoleon was infested with scabies during the Russian campaign. Severe itching lead to infections and fatigue, which reduced their skin to a bleeding mess in frenzies of scratching. It may well be that this contributed in large part to France's loss of the military campaign. It is also speculated that Napoleon's famous pose with his hand inside his coat was made because he was scratching scabies.

Treatment

Scabies is not going to go away on its own. You must get it treated. The itch of scabies is so severe that people can be driven to distraction and exhausted by lack of sleep. Scratched areas are vulnerable to secondary infection with bacteria- impetigo.

Lindane, Kwell, lotion (gamma benzene hexachloride) used to be the most popular treatment in America. It has fallen out of favor because of concern about neurotoxicity in babies. I do not think you can buy it anymore. A single application brings cure in 99% of cases. Starting in the late 1970's we started seeing cases of Kwell resistant scabies, mostly from California.

Now we use safer but more cumbersome treatments. These include:

Crotamiton Cream- Eurax
5% permethrin cream
5% precipitated sulfur in Vaseline

Of these, 5% permethrin is the most pleasant. Bugs can develop resistance to chemical molecules like lindane, crotamiton, and permethrin, but not commonly. This is because these are organic molecules. However, they cannot develop resistance to sulfur because it is an element and not an organic molecule. Sulfur is an obnoxious treatment, but it never fails, and it is safe.

Whatever type of medicine you choose, apply it from the neck to the toes everywhere. Leave it on 8 hours and wash it off. If it becomes irritating, wash it off right away. Don't leave it on 8 hours if you are reacting to it. It is best to use it three nights and then wash your sheets. You do not need to fumigate the house or your clothes. Eggs hatch in 2 weeks. Set blankets aside two weeks. If the eggs hatch and you are not there to serve as food for them, they will die, at least in theory.

Let me say one more thing. Now, let's say you have gotten the right diagnosis and had the treatment. You are going to continue to be itchy about 5-14 days longer. The dead bugs and their dead eggs are still in the outer layer of dead skin giving a poison ivy like reaction. You just have to wait for the growth of the skin to cause the contaminate layer to be shed. Do not try to scrub it off.

The information provided in these patient information sheets is offered for general informational and educational purposes only; it is not offered as and does not constitute medical advice. In no way are any of the materials presented meant to be a substitute for professional medical care or attention by a qualified practitioner, nor should they be construed as such.

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