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Scabies

Basic Information

Scabies is an infectious, extremely itchy rash caused by the mite Sarcoptes scabiei hominus. It is spread by intimate contact, either by sleeping with a person who is infested with the mites or by picking up the mites in the bedding or towels of an infected person. Thus it is often diagnosed as a sexually transmitted disease (STD), though it differs from other sexually transmitted diseases in that it is not particularly prevalent among young adults or gay men. It is most prevalent among children in underdeveloped countries, but in developed countries like the U.S. it is spread evenly across all age groups and affects males and females equally.

Scabies has been recognized since the Middle Ages and has been referred to since then as the "seven-year itch" but it has not been until this century that the rash has been recognized as being caused by the mite itself.

The infection is often associated with poor or unhygienic living conditions and is seen most frequently in crowded environments, such as nursery schools, nursery homes, large families in single homes or even in hospitals.

Though scabies is often classified as a sexually transmitted disease, it is important to remember that it is transmitted by skin-to-skin contact, not by engaging in a specific sexual act. The common occurrence of scabies in infants and children supports skin-to-skin transmission and the infection in young children do not in most cases imply sexual exposure. But scabies acquired as a sexually transmitted disease is suspected when a patient has engaged in sex with multiple sexual partners.

The theory that epidemics of scabies occur in 30-year cycles -- 15 years of widespread prevalence followed by 15 years of general quiet -- has been more recently challenged and the epidemics have been attributed to periods following social upheavals such as World War I and II. The mite infests at least 40 different mammals, infecting a greater number of living hosts than any other parasite. Also it is known that domestic animals, most usually dogs, transmit scabies to humans.

Scabies can infest the skin from neck to toe -- but -- in the old, the young, or in patients with a compromised immune system, the face and scalp can be infested as well. Patients who have AIDS (acquired immune deficiency syndrome) have a higher incidence of infection.

The female mite is the primary culprit responsible for the rash. About the size of the head of a pin and thus barely noticeable to the naked eye (although it can be seen without magnification), the female mite can walk, say, all the way from the neck down to the hands in just a few hours. Then, choosing a site, the fertilized female burrows down a short distance into the skin and begins to lay her eggs, usually laying 2--3 eggs per day before burrowing down into the skin a little further and laying 2--3 more eggs. Under the right conditions the mite can lay eggs for a month and never return to the surface. But it is thought that only 10% of the eggs reach adulthood. They do not survive for a variety of reasons including the patient's natural immunological reaction, intense scratching and bathing. The typical patient has an infestation of no more than 11 mites, with nearly 50% of patients having no more than 5.

The burrows or lesions (short, irregular lines which often have a vesicle or tiny papule at one end) are most often found on the wrists, web spaces of the hands, knees, legs, penis, breasts, buttocks and the scrotum. This is thought to be because the female mite tends to seek protection from the colder areas involving the face and scalp. These are also thought to be attractive areas for infection by the mite because they are usually places where there are natural body creases or areas where belts, straps or bands constrict and cling to the skin.

A tiny burrow (2 to 3 mm) is the primary lesion caused by the scabies mite -- but it is often hidden by the secondary lesion or eruption (minute, purplish-red papules) which is exacerbated by scratching or infection.

Mites cannot survive in the cold and actually die also from exposure to heat yet they can survive off the host for several days in a warm, moist environment, thus providing an indirect form of transmission via towels or bedding.

Symptoms

It is not until after a month that the rash appears. But the earliest symptoms of a scabies infection can be nighttime itching, occasionally before the rash appears. But the significant and intense itching that one associates with scabies infection occurs 30 days after the infestation. This is probably due to sensitization. The medical term for this itching of the skin is called pruritus.

Crusted scabies are most often seen in patients with impaired immune systems. The lack of immune response permits the lesions' scales to contain a great number of mites who multiply unchecked. The lesions typically resemble psoriasis and the intense nighttime itching or pruritus is not as prevalent. It takes a number of months for crusted scabies to develop and the shedding of large numbers of mites causes this kind of scabies to be the most contagious.

Diagnosis/Treatment

A diagnosis is usually made by your health care provider by direct examination of your skin. The rash is most often identified by following the burrow of the mite, linear in nature, which consists of purplish-red pimple-like bumps or bites normally formed in a row. The rash is really an allergic reaction and sometimes mites might not even be in the site of the rash itself.

Occasionally the tiny mite can be seen by the naked eye, but normally your health care provider will want to scrape your skin to get the mite onto a slide where it can be examined by a microscope. Lesions on the finger webs or wrists are thought to be the areas most likely to discover the mites and hence make a positive diagnosis for scabies. The scraping of the skin should be done by putting a drop of mineral oil on the lesion after which a small scalpel is gently scraped across the surface to remove the topmost layers of skin. This is almost always painless and bleeding should not occur. A drop of mineral oil is used so that the fecal pellets of the mites are not destroyed -- sometimes the only evidence with which to make a positive diagnosis.

Treatment of scabies generally consists of applying an insecticide lotion or cream on the skin -- the four drugs used are lindane (the most frequently prescribed), permethrin, crotamiton, and sulfur.

  • Lindane -- After bathing, lindane is applied from the neck down and washed off after twelve hours. It usually eradicates the infestation by this primary application, but your health care provider may recommend a second application if there has been a treatment failure or re-infestation. Lindane is not recommended for young children or pregnant women because of possible toxicity.
  • Permethrin -- This cream needs to be applied from the neck down and massaged into the skin and washed off after 8--14 hours. It is most often recommended for young children and pregnant women because of its lack of toxicity. One application is usually enough to rid the patient of the infestation.
  • Crotamiton -- Again, because of the lack of toxicity, this cream is usually recommended for young children and pregnant women. It is applied after bathing from the neck down, re-applied after 24 hours, then washed off 48 hours after the second application.
  • Sulfur -- This has been a treatment used for centuries since the "seven-year itch" began and today will still usually eradicate the infestation. It is applied from the neck down for three consecutive nights, then washed off 24 hours after the last application. This treatment is not used as frequently today because of the unpleasant odor and its proclivity to stain clothing.

The decision about which medication to use should be made by your health care provider based on evaluation of the individual patient. As stated, certain medications will not be appropriate for young children or pregnant women. Do not attempt to cure yourself by using homemade remedies or concoctions. If you feel you might have scabies, contact your health care provider.

The good news is that medications used by most patients eradicate the disease and most patients respond well to the drugs. But you must be sure to follow your health care provider's instructions for the proper use of lotions or medications.

Within ten days of treatment, the severe itching usually subsides, although it can continue for up to two weeks. Do not continue to use the medications unless otherwise indicated because overuse of medication could cause a skin condition or rash that might be erroneously associated with treatment failure. If symptoms do not disappear, you may have to be treated again. Try not to scratch or irritate the rash. Your health care provider may treat the itching with topical, soothing ointments. Also, your health care provider will probably want to prescribe antibiotics if a secondary infection occurs.

Scabies is not a reflection of your personal habits of cleanliness -- anyone can become infested. That is why preventive or prophylaxis treatment is usually indicated for household contacts or sexual partners -- remember there are usually no symptoms until one month following infestation when the rash finally appears. Whether other contacts the infected patient has had should be treated depends on the skin-to-skin contact they have had with the patient or by the use of linens they have shared with the patient. If you have been diagnosed with scabies you should wash your hands frequently to avoid the spread of scabies. Use soapy, hot water to wash bed linens, towels, clothes, toys, then machine dry. Vacuum the house and throw out the bag -- remember mites can live off the host for 2--3 days in the right warm, moist conditions.

In nursing homes or extended care facilities where an infestation has occurred, treatment should be given to staff, patients and visitors whether they present symptoms or not. This will substantially reduce opportunities for reinfestation.

As mentioned, a case of scabies in a child does not usually indicate a case of sexual transmission, however if you feel this case derives from a possible or probable form of sexual abuse (most often by an infected adult, usually a relative of the child's), the child diagnosed with scabies should be further investigated for the presence of other STDs.

Patients with AIDS may not present the typical patterns of scabies infestation. For instance there may be no burrows and the lesion patterns may not be linear. The crusted scabies, resembling psoriasis, may not be as readily recognized or diagnosed and repeated treatments are usually necessary to eradicate the large number of mites.

Since scabies is often diagnosed as a sexually transmitted disease it is important that you notify your sexual partners so that they may seek treatment, and do not engage in further sexual activity until you have followed up with your health care provider to be sure you are no longer infectious. Treatment should always be administered by your health care provider since when one sexually transmitted disease is present, others might be present as well. Your health care provider might want to test you for syphilis, gonorrhea, chlamydia, herpes and hepatitis B. As well, a discussion about HIV testing and counseling is very important and indicated.

Should you even suspect that you have scabies or any sexually transmitted disease, please see your health care provider promptly.

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