Scabies

Scabies is a skin disease caused by a parasitic mite called sarcoptes scabiei. This mite infects millions of people each year. The disease is very common in tropical regions with the prevalence as high as one-hundred percent in South and Central America. It occurs in all age groups and is transmitted from person to person by direct contact. Children can pass the mite along during play. Sexual partners may transmit it to one another.

Healthcare workers providing care to patients may acquire and transmit the disease. Mites can live for up to four days without a human host. This implies that scabies may also be spread by indirect contact, such as through clothing, towels and bedding. Very often outbreaks occur in large institutions, such as nursing homes; this supplies further evidence that the disease is easily transmitted in ways other than direct contact.

The female mite, sarcoptes scabiei, will tunnel under the epidermis or top layer of human skin. The female lives for four to six weeks and during that time she will lay two to three eggs per day. The eggs will hatch in approximately 72 hours. The larvae or that which is hatched from the egg, moves back to the surface of the skin and in about two weeks becomes a mature adult ready to mate. The mature adult female mite can then re-infect the skin. The male adult mites are much smaller that the females. They remain on the surface of the skin and die shortly after mating.

Scabies causes allergic response of the human host to the mites themselves, as well as their feces and eggs. Resultant rash is extremely itchy and disturbing.

Presentation:
The symptoms of scabies include a rash and severe itching that begins anywhere from three to six weeks after exposure in an initial infection. The itching is worse at night, especially after a warm bath or shower. The rash begins as small, red bumps that can progress to larger blisters, pus bumps or nodules. Crusting may occur in patients with a compromised immune system. The classic feature is a linear burrow which is a grey or skin colored ridge, approximately 0.5 to 1.0 cm in length.

The burrow can be straight or wavy and may have a small bump at the end of the tunnel signifying where the mite resides. Each female mite produces one burrow. The rash is usually more pronounced in the armpits, in the web space of the fingers, on the sides of the fingers and the wrists. Other areas affected include the breasts in females, the penis and scrotum, the buttocks, the waist-line and the elbows. The face, scalp and
neck are usually spared except in infants. It is also more commonly seen on the palms and soles in small children. In general, the rash of scabies may appear anywhere on the body but tends to be concentrated on the hands, feet, and in body folds.

Diagnosis:
Scabies is usually diagnosed by the history you relay to your doctor and by the characteristic rash. If the diagnosis is unclear, your doctor may wish to confirm it by examining scrapings from the rash under a microscope where he or she may detect the female mite, eggs and/or feces.

Treatment:
Individuals who have been infected with scabies and all close physical contacts should be treated simultaneously whether or not symptoms are present. Treatment consists of application of a topical cream to all areas of the body, from the neck downward. The cream must be left on for eight to twelve hours and then washed off. Despite treatment, new lesions may continue to erupt as additional eggs hatch and the larvae re-infect the skin. For this reason, repeated treatments are often necessary to completely eradicate the mite. There are several types of creams available for treatment of scabies.

The two most commonly prescribed treatments are permethrin (brand name Elimite) and lindane (brand name Kwell). Alternative topical treatments include crotamiton cream, sulfur-based creams, benzyl benzoate, esdepallethrine, malathion and ivermectin. Treatment of scabies with oral medication is reserved for refractory cases, in those in which application of a cream would be impractical or difficult (such as patients who are mentally impaired or in large institutional outbreaks), and in patients with a compromised immune system.

It is important to realize that the itching associated with scabies may persist for up to four weeks after successful treatment. This is due to an allergic reaction to the mite feces and not due to a persistent infection. It takes that length of time for the skin to slough any residual debris and for the allergic reaction to subside. During this time your doctor may prescribe antihistamines or a topical corticosteroid cream to alleviate itching.

Equally important for the successful treatment of scabies is controlling for environmental sources of the mite. Mites can survive for up to four days without a human host; therefore, all linens, towels and clothing used in the previous four days, must be decontaminated. This can be achieved by washing in hot water (60 degrees Celsius) and through heated drying. If an item can not be washed then it should be dry-cleaned or sealed in a plastic bag for five days. Treatment failures can usually be attributed to inadequate eradication of the mite in a patient’s environment, rather than ineffective medication.

Andrea Baratta, D.O.
Dermatology Department
St. John’s Episcopal Hospital South Shore
Far Rockaway, NY