Scabies Information

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Scabies

Scabies is a transmissible ectoparasite skin infection characterized by superficial

burrows, intense pruritus (itching) and secondary infection. The word scabies comes

from the Latin word for "scratch" (scabere).

Scabies is caused by the mite Sarcoptes scabiei, variety hominis, as shown by the

Italian biologists Diacinto Cestoni in the 18th century. It produces intense, itchy skin

rashes when the impregnated female tunnels into the stratum corneum of the skin and

deposits eggs in the burrow. The larvae, which hatch in 3-10 days, move about on the

skin, molt into a "nymphal" stage, and then mature into adult mites. The adult mites

live 3-4 weeks in the host's skin.

The motion of the mite in and on the skin produces an intense itch which may resemble

an allergic reaction in appearance. The presence of the eggs produces a massive

allergic response which, in turn, produces more itching.

Scabies is transmitted readily, often throughout an entire household, by skin-to-skin

contact with an infected person (e.g. bed partners, schoolmates, daycare), and thus is

sometimes, although inaccurately, classed as a sexually transmitted disease. Spread

by clothing, bedding, or towels is a less significant risk, though possible.

When Will I Start To Develop Symptoms

It takes approximately 4-6 weeks to develop symptoms after initial infestation. Therefore,

a person may have been contagious for at least a month before being diagnosed. This

means that person might have passed scabies to anyone at that time with whom they

had close contact. Someone who sleeps in the same room with a person with scabies

has a high possibility of having scabies as well, although they may not show symptoms.

The symptoms are caused by an allergic reaction that the body develops over time to

the mites and their by-products under the skin, thus the 4-6 week "incubation" period.

There are usually relatively few mites on a normal, healthy person — about 11 females

in burrows. Scabies are microscopic although sometimes they are visible as a pinpoint

of #016EBB. The females burrow into the skin and lay eggs there. Males roam on top of the

skin, however, they can and do occasionally burrow. Both males and females surface

at times, especially at night. They can be washed or scratched off (however scratching

should be done with a washcloth to avoid cutting the skin as this can lead to infection),

which, although not a cure, helps to keep the total population low. Also, humans

create antibodies to the scabies mites which do kill some of them.

SIgns, Symptoms and Diagnosis

A delayed hypersensitivity (allergic) response resulting in a papular eruption (red,

elevated area on skin) often occurs 30-40 days after infestation. While there may

be hundreds of papules, fewer than 10 burrows are typically found. The burrow

appears as a fine, wavy and slightly scaly line a few millimeters to one centimeter

long. A tiny mite (0.3 to 0.4 mm) may sometimes be seen at the end of the burrow.

Most burrows occur in the webs of fingers, flexing surfaces of the wrists, around

elbows and armpits, the areolae of the breasts in females and on genitals of males,

along the belt line, and on the lower buttocks. The face usually does not become

involved in adults.

The rash may become secondarily infected; scratching the rash may break the skin

and make secondary infection more likely. In persons with severely reduced immunity,

such as those with HIV infection, or people being treated with immunosuppressive

drugs like steroids, a widespread rash with thick scaling may result. This variety

of scabies is called Norwegian scabies.

Scabies is frequently misdiagnosed as intense pruritus (itching of healthy skin) before

papular eruptions form. Upon initial pruritus the burrows appear as small, barely

noticeable bumps on the hands and may be slightly shiny and dark in color rather

than red. Initially the itching may not exactly correlate to the location of these bumps.

As the infestation progresses, these bumps become more red in color.

Generally diagnosis is made by finding burrows, which often may be difficult because

they are scarce, because they are obscured by scratch marks, or by secondary

dermatitis (unrelated skin irritation). If burrows are not found in the primary areas

known to be affected, the entire skin surface of the body should be examined.

The suspicious area can be rubbed with ink from a fountain pen or alternately a topical

tetracycline solution which will glow under a special light. The surface is then wiped off

with an alcohol pad; if the person is infected with scabies, the characteristic zigzag or

S pattern of the burrow across the skin will appear.

When a suspected burrow is found, diagnosis may be confirmed by microscopy of

surface scrapings, which are placed on a slide in glycerol, mineral oil or immersion in

oil and covered with a coverslip. Avoiding potassium hydroxide is necessary because

it may dissolve fecal pellets. Positive diagnosis is made when the mite, ova, or fecal