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Scabies
[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
used).
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
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.
