Page 182 - fourth year book

SKIN DISEASES

IV- Parasitic infection

Scabies

Scabies is a contagious skin disorder caused by infestation with
microscopic mite. Sarcoptes - scabiei Infestation is common, found
worldwide, and affects people of all races and social classes.

Etiology: (lifecycle fig. 2)

The female parasite penetrates the skin. During her passage in the
stratum corneum, it deposits ova about 20-50 ova in a course of 2 weeks.

In addition to the ova, the tunnel presents many dark spots, which
represents the feces of the parasite. The male dies after copulation and
the female after all the ova are laid. In 4-8 days larva are hatched then
transformed into nymph within few days. Nymph matures to adult male
and female after few days. Copulation occurs, and on scratching, the
tunnels are excoriated and the parasites become on the surface of the
skin and the life cycle will be repeated.

Incubation period:

It is about one month during this period sensitization occurs. In second
attack this period is shorten because the patient has already been

sensitized.

Ova 4-8 days Larva Few days Nymph Few days Mature
Modes of transmission

1. Direct, prolonged, skin-to-skin contact with a person already
infested with scabies.

2. Infestation is easily spread to sexual partners and household
members.
3. In direct: by sharing clothing, towels, and bedding.
4. From animals: Dogs, Cats, rabbits, sheep, and camels.

Signs and Symptoms

1. Pimple-like irritations, burrows or rash of the skin, especially the
webbing between the fingers; the skin folds on the wrist, elbow, or
knee; the penis, the breast, or shoulder blades.

2. Intense itching, especially at night and over most of the body.
3. Sores on the body caused by scratching. These sores can sometimes
become infected with bacteria.

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