Human Diseases and Conditions

What is scabies?

Scabies is an itchy, highly contagious skin condition caused by 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 that infest humans are female and are 0.3 mm-0.4 mm long; the males are about half this size. Scabies mites can be seen with a magnifying glass or microscope. The scabies mites crawl but are unable to fly or jump. They are immobile at temperatures below 20 C, although they may survive for prolonged periods at these temperatures.
Scabies infestation occurs worldwide and is very common. It has been estimated that worldwide, about 300 million cases occur each year. Human scabies has been reported for over 2,500 years. Scabies has been reported to occur in epidemics in nursing homes, hospitals, long-term care facilities, and other institutions. In the U.S., it is seen frequently in the homeless population but occurs episodically in other populations of all socioeconomic groups as well.

How is scabies spread?

Direct skin-to-skin contact is the mode of transmission. Scabies mites are very sensitive to their environment. They can only live off of a host body for 24-36 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. Sexual physical contact, however, can transmit the disease. In fact, sexual contact is the most common form of transmission among sexually active young people, and scabies has been considered by many to be a sexually transmitted disease (STD). However, other forms of physical contact, such as mothers hugging their children, are 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 prolonged personal contact necessary for transmission of the mites.

 signs and symptoms

Scabies signs and symptoms include:

• Itching, often severe and usually worse at night
• Thin, irregular burrow tracks made up of tiny blisters or bumps on your skin

The burrows or tracks typically appear in folds of your skin. Though almost any part of your body may be involved, in adults scabies is most often found:

• Between fingers
• In armpits
• Around your waist
• Along the insides of wrists
• On your inner elbow
• On the soles of your feet
• Around breasts
• Around the male genital area
• On buttocks
• On knees
• On shoulder blades

In children, common sites of infestation include the:

• Scalp
• Face
• Neck
• Palms of the hands 
• Soles of the feet

 Causes

The eight-legged mite that causes scabies in humans is microscopic. The female mite burrows just beneath your skin and produces a tunnel in which it deposits eggs. The eggs mature in 21 days, and the new mites work their way to the surface of your skin, where they mature and can spread to other areas of your skin or to the skin of other people. The itching of scabies results from your body's allergic reaction to the mites, their eggs and their waste.
Close physical contact and, less often, sharing clothing or bedding with an infected person can spread the mites.
Dogs, cats and humans all are affected by their own distinct species of mite. Each species of mite prefers one specific type of host and doesn't live long away from that preferred host. So humans may have a temporary skin reaction from contact with the animal scabies mite. But people are unlikely to develop full-blown scabies from this source, as they might from contact with the human scabies mite.

 Dignosis:

To diagnose scabies, your doctor examines your skin, looking for signs of mites, including the characteristic burrows. When your doctor locates a mite burrow, he or she may take a scraping from that area of your skin to examine under a microscope. The microscopic examination can determine the presence of mites or their eggs.

Treatment:

Skin lotions containing permethrin, lindane or crotamiton are available through a physician's prescription for the treatment of scabies. The lotions are applied to the whole body except the head and neck. Sometimes, itching may persist but should not be regarded as treatment failure or reinfestation. Persons who have had skin contact with an infested person (including family members, roommates, direct care providers and sexual contacts) should also be treated.

 Prevention:

Avoid physical contact with infested individuals and their belongings, especially clothing and bedding. Health education on the life history of scabies, proper treatment and the need for early diagnosis and treatment of infested individuals and contacts is extremely important.

REFERENCES:

Chosidow, O. "Clinical Practices. Scabies." N Engl J Med 354.16 Apr. 2006: 1718-1727.
Dourmishev, A.L., L.A. Dourmishev, and R.A. Schwartz. "Ivermectin: Pharmacology and Application in Dermatology." Int J Dermatol 44.12 Dec. 2005: 981-988.
McCroskey, Amy L., and Adam J. Rosh. "Scabies." eMedicine.com. Apr. 5, 2010. <http://emedicine.medscape.com/article/785873-overview>.
United States. Centers for Disease Control and Prevention. "Scabies." Nov. 10, 2008. <http://www.cdc.gov/scabies/index.html>.