Scabies

Scabies is a contagious skin condition that causes skin eruptions and intense itching.


Causes/associated factors
Scabies is caused by an infestation with the microscopic mite Sarcoptes scabiei. Using its legs and mouth, the mature female S. scabiei burrows into the top layer of skin to lay her eggs. Within three weeks, the larvae hatch and grow to adulthood on the surface of the skin, ready to repeat the cycle. The female mite can survive on her host for four to six weeks.
A mite infection in pets is known as "mange." These mites are not the same S. scabiei mite, but can cause irritation and itching if they get on your skin. They'll only stay a few days and will not reproduce on your skin, however. Be sure to get treatment for your animal.

Anyone can contract scabies, but the condition is most common in children and young adults.


Transmission
Scabies spreads through skin-to-skin or sexual contact with an infected person, even with adequate levels of personal hygiene on the part of the host. Skin contact is generally necessary because the mites don't fly or jump. The risk increases with prolonged contact. Because the mite can survive for two to three days off of its human host, you can also contract scabies by touching recently infected clothing or linens.
The risk of contracting scabies is highest in crowded or unsanitary living conditions. People who have weak immune systems are at an increased risk. Norwegian scabies, a severe form of scabies, is more common if you have a weak immune system, are malnourished, or do not experience the characteristic itching of scabies, which may happen if you have a neurological disorder, such as Down syndrome or dementia.

When you're infected with S. scabiei for the first time, your body develops a type of allergic reaction to the mite. It takes about four to six weeks for this reaction to develop. With any subsequent infections, however, symptoms typically develop within one to four days because your body is sensitized through previous exposure. Reinfections are generally less severe.

You're infectious (capable of spreading the infection) from the time you're infected -- even before symptoms develop -- until your treatment is complete.


Signs/symptoms
For older children and adults, mites often burrow in the folds of skin in the upper extremities, especially at the wrists and elbows, under the arms, and between the fingers. The navel and belt line areas, buttocks, men's genitals, and women's breasts and pubic area may also be affected. For infants and young children, scabies may also strike the scalp, head, and palms of the hands or soles of the feet.
Symptoms of scabies often include intense itching, especially at night or after a hot bath, and a rash that may include:

burrows (irregular, fine, wavy or slightly scaly brown lines about the width of a hair) a few millimeters to 1 centimeter long that may appear gray or inflamed
small, itchy blisters or raised red skin, usually in a line
broken blisters that leave scratch marks and thickened skin or scaling
The mite is sometimes seen as a tiny black dot within the burrows or blisters. Norwegian scabies typically has a widespread rash of crusted sores and may not be itchy.


Diagnosis
The combination of itching and burrows may lead your doctor to suspect scabies. To confirm the diagnosis, skin scrapings from the end of a burrow may be examined under a microscope. When a burrow is not apparent, a special ink can be applied to the rash and then washed with alcohol. The area usually remains stained for scraping. Skin biopsy (taking a tissue sample for further evaluation) is rarely done, but will also identify the mite.

Treatment
To clear up the infestation, your doctor may prescribe a medicated skin lotion such as permethrin. You may be directed to apply the lotion from your neck down, leave it on for several hours, and then wash it off. Avoid skin-to-skin contact with anyone for 24 hours after your treatment or as directed by your doctor. Children should not return to school or a child care setting until after treatment is complete. Your doctor may also suggest a follow-up exam several weeks later. A second round of treatment may be needed, especially if the infestation is heavy. To avoid potentially serious side effects, it's important to carefully follow your doctor's specific directions.
An oral medication called ivermectin may be prescribed, especially for people who have weak immune systems. It may be combined with a medicated skin lotion to treat Norwegian scabies.

Mites can survive up to three days in infected clothing, towels and bedding, so wash linens and items worn next to the skin in hot water. Dry them on a high-heat setting in the dryer. Clothing that can't be laundered should be stored for several days to give the mites time to die. Bathe thoroughly and, if you've been diagnosed with Norwegian scabies, vacuum your home carefully.

Because the itching of scabies is caused by a hypersensitive response to the mite, it may last a few weeks after a successful treatment is complete. If this happens to you, don't assume the treatment has failed. Your doctor may recommend an oral antihistamine, a steroid cream or calamine lotion to ease the itching. Sometimes, small red-brown itchy nodules, especially near the genitals, groin, buttocks or armpit, may last for months after a successful treatment.

Because scabies spreads so easily, household members are generally treated simultaneously -- even before symptoms develop.


Complications
Repeated scratching of itchy skin can cause breaks in the skin that allow bacteria to enter your body. If this happens, you may develop a bacterial skin infection that requires antibiotic treatment. Seek medical attention if you notice signs of infection, which may include:
increased redness, swelling, pain or tenderness
warmth to the touch of the affected area
red streaks coming from the affected area
pus-like drainage
a general ill feeling
fever

Pregnancy-specific information
If you're pregnant, carefully discuss the treatment options with your doctor. Some medications can be harmful to a developing fetus. Crotamiton and sulfur are considered the safer options during pregnancy.

Senior-specific information
Older adults may have fewer sores but more intense itching. If an illness has weakened your immune system, you have a greater risk of extensive infestation.

Prevention
To prevent scabies, practice good personal hygiene, launder your clothing often, and avoid close contact with anyone who's infected. It's also a good idea to avoid sharing clothing and linens. After direct exposure to scabies, prompt treatment can help prevent outbreaks.