Scabies 200501

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    [Sarcoptes scabei]

    Causal Agent:

    Sarcoptes scabei, human itch or mange mites.

    The mites burrow into the skin but never below thestratum corneum. The burrows appear as raisedserpentine lines up to several centimeters long.

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    Sarcoptes scabeimite.Females are 0.3-0.4 mm long and 0.25-0.35 mm wide.

    Males are slightly more than half that size.

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    Sarcoptes scabeiundergoes egg, larva, nymph and adult.

    Females deposit eggs as they burrow through the skin. After

    the eggs hatch, the larvae migrate to the skin surface and

    burrow into the intact stratum corneum to construct almostinvisible, short burrows called molting pouches. After larvae

    molt, a nymphs is released. The nymphs molts into slightly

    larger nymphs before molting into adults. Larvae and nymphs

    may often be found in molting pouches or in hair follicles and

    look similar to adults, only smaller. Mating occurs after the

    nomadic male penetrates the molting pouch of the adult

    female. Impregnated females extend their molting pouches

    into the characteristic serpentine burrows, laying eggs in the

    process. The impregnated females burrow into the skin andspend the remaining 2 months of their lives in tunnels under

    the surface of the skin. Males are rarely seen. They make a

    temporary gallery in the skin before mating.

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    Transmission occurs by the transfer of ovigerous

    females during personal contact.

    Mode of transmission is primarily person to person

    contact, but transmission may also occurvia fomites

    (e.g., bedding or clothing).

    Mites are found predominantly between the fingers

    and on the wrists, later on elbows and the rest of the

    body. The buttocks, women's breasts and externalgenitalia may be involved.

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    Cross sectional view of the burrows created in theepithelium by Sarcoptes scabei.

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    Clinical FeaturesScabies itch is due to the sensitization of the patient to the

    mite and eggs and is characteristically nocturnal. Septicpustules may develop after scratching, if the hygiene is poor.

    When a person is infested with scabies mites for the first time, there is

    usually little evidence of infestation for the first month (range 2 to 6 weeks).

    After this time and in subsequent infestations, people usually become

    sensitized to mites and symptoms generally occur within 1 to 4 days. Mitesburrowing under the skin cause a rash, which is most frequently found on

    the hands, particularly the webbing between the fingers; the folds of the

    wrist, elbow or knee; the penis; the breast; or the shoulder blades. Burrows

    and mites may be few in number and difficult to find in some cases. Most

    commonly there is severe itching, especially at night and frequently overmuch of the body, including areas where no mites are living. Complications

    due to infestation are usually caused by secondary bacterial infections

    from scratching.

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    Scabies lesions are caused by Sarcoptes scabei

    burrowing under the skin. A typical location is on the

    hands, particularly the webbing between the fingers.

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    Laboratory DiagnosisMost diagnoses of scabies infestation are made based upon theappearance and distribution of the rash and the presence of

    burrows. Whenever possible scabies should be confirmed byisolating the mites, ova or feces in a skin scraping. Scrapingsshould be made at the burrows, especially on the handsbetween the fingers and the folds of the wrist. Alternatively,mites can be extracted from a burrow by gently pricking open

    the burrow with a needle and working it toward the end wherethe mite is living.

    Diagnosis is made by characteristic rash,

    smearing black ink on the skin and observingburrows when ink is wiped. Microscopicexamination of the skin scraping showmites.

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    Skin Scraping Technique.

    The diagnosis can be confirmed by demonstration of the mites, eggs, or scybala (fecal

    pellets). Because the mites are located under the surface of the skin, scrapings must be

    made from the infected areas.

    1. Place a drop of mineral oil on a sterile scalpel

    blade. (Mites will adhere to the oil, skin scales will mix with oil, the refractility

    differences will be greater between the mite and the oil, and the oil will not

    dissolve fecal pellets.)

    2. Allow some of the oil to flow onto the papule.

    3 . Scrape vigorously six or seven times to remove the top of the papule. (There

    should be tiny flecks of blood in the oil.)

    4. Transfer the oil and scraped material to a glass(an applicator stick can be


    5. Add 1 or 2 extra drops of mineral oil to the slide and stir the mixture. Any large

    clumps can be crushed to expose hidden mites.

    6. Place a coverslip on the slide, and examine (first on low power). The adult mites

    range from approximately 215 to 390 um in length, depending on sex. The eggs-

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    Treatment involves swabbing of the whole body from neckdown with 1% malathion or benzene hexachloride(crotamiton for infants). Topical steroids must not be used. Ifpossible, the whole family should be treated. Several lotionsare available to treat scabies. The treatment of choice is the

    topical use ofpermethrin. Ivermectin* is an alternative drugthat is effective for crusted scabies in immunocompromisedpersons. A second treatment with the same lotion may benecessary 7-10 days later.All clothes, bedding, and towels used by the infested

    person during the treatment should be washed in hot water,and dried in a hot dryer.Contact with infested person should be avoided.

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    Geographic Distribution

    Scabies mites are distributed worldwide, affecting all races and

    socioeconomic classes in all climates.

    Epidemics of the disease may occur in long periods but mites

    may be common at all times in very poor communities with

    inadequate washing facilities.