Sarcoptes scabei undergoes four stages in its life cycle; egg, larva, nymph and adult.  Females deposit eggs at 2 to 3 day intervals as they burrow through the skin .  Eggs are oval and 0.1 to 0.15 mm in length and incubation time is 3 to 8 days.  After the eggs hatch, the larvae migrate to the skin surface and burrow into the intact stratum corneum to construct almost invisible, short burrows called molting pouches.  The larval stage, which emerges from the eggs, has only 3 pairs of legs , and this form lasts 2 to 3 days.  After larvae molt, the resulting nymphs have 4 pairs of legs .  This form 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.  Adults are round, sac-like eyeless mites.  Females are 0.3 to 0.4 mm long and 0.25 to 0.35 mm wide, and males are slightly more than half that size.  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 and spend 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. Transmission occurs by the transfer of ovigerous females during personal contact.  Mode of transmission is primarily person to person contact, but transmission may also occur via fomites (e.g., bedding or clothing).  Mites are found predominantly between the fingers and on the wrists.  The mites hold onto the skin using suckers attached to the two most anterior pairs of legs.

Scabies has been labeled with an age-old nickname as the "itch" or "the seven year itch". It is a contagious skin irritation and is caused by a very tiny insect called the "itch mite". The varieties of such mites that establish on human beings seem to confine themselves to people, and those types that are on animals don't seem to pass to people. These mites are about the size of a dot at the end of a sentence. They are grayish in color and nearly transparent. Scabies is most commonly found among crowded groups. The mite is transmitted through close bodily contact. Clothing and bedding of infested individuals apparently play only minor roles in the spread of the infection. Due to the frequency of such infections on the hands, shaking hands, holding, or clasping hands as in children's games can be a method of transfer. The mites do not survive more than a few days if apart from the body.

The female scabies mite burrows or tunnels into the outer layer of skin in a tiny red line about a half-inch long and then lays eggs. Such a burrow is usually very hard to see or find on people. Usually the parasite will tend to first locate in the webs between the fingers or toes, around the wrist or about the navel. It can also be commonly found on the back of elbows, the folds or the armpits, the beltline and abdomen, about the creases of the groin, and on the genital organs. Small children, especially babies, often have involvement of the face, scalp, palms of the hands, or soles of the feet, but this would be very unusual in adults.

Some people may become allergic or very sensitive to the presence of scabies on the skin and will develop extensive areas of inflamed, reddened, itching skin as a reaction to the insect or its waste products.

If an individual has an itching skin irritation on the areas mentioned and tiny reddened dots with surrounding redness or streaks of redness and evidences of scratching, there should be a high level of suspicion for scabies. The rash and itching may not be apparent until as much as a month or six weeks after contracting the mites.

There seems to be particularly more itching at night. Some people can be carriers and not know it or show it. Tiny blisters can occur on scabies areas and when scratched, small infected sores develop. Although there is a high degree of suspicion for scabies if such skin conditions are present, definite proof of the presence of scabies is based on actually finding and recognizing the parasite. They can be spotted with a hand lens.

Once the diagnosis is established, treatment usually consists of an application of a creme or lotion containing the scabies-killing insecticide. The drug of choice is 5% permethrin, a synthetic pyrethroid(Elimite). Permetherin should be removed by bathing after 8 to 14 hours. One application of permetherin is currative. Alternative drugs are Crotamiton-10%(Eurax) or lindane (Kwell, Scabene) all of these drugs are available by prescription only. Sometimes two or more cremes or lotions are prescribed, but usually only one is necessary. If crusted sores are present on the skin, often a warm bath is recommended prior to application of the lotion or creme to soften the crusts. If a bath is used, allow the skin to dry and cool before applying the lotion or creme. A total body application should be made from the neck down. Scabies rarely affects the heads of children or adults, but this may occur in infants.

Always follow the directions provided with the lotion or creme. Itching may persist 1-2 weeks after treatment. If skin sores appear after treatment, perhaps re-treatment is necessary. Only 5% of cases treated with crotamiton or lindane require re-treatment. If re-treatment is needed, generally it is done 7- 10 days after the initial treatment. Routine laundering of bedding, clothing, and towels is advised of items used within the 48 hours prior to treatment. Treatment of close contacts or other family members may also be carried out simultaneously.

Information courtesy of Seattle and King County Public Health
at (http://www.metrokc.gov/health/)

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