Scabies - Explained

Scabies

Etiology

Scabies is caused by the female crab shaped itch mite (Sarcoptes or Acarus scabiei). Scabies is highly prevalent during periods of overcrowding, such as occurs during wars. Since the 1960s, however, there has been a rise in the incidence of scabies worldwide. The reason for the pandemic is unknown and is thought to be multifactorial, including sexual promiscuity, increased worldwide travel, and ecologic changes. Scabies is usually transmitted by prolonged contact, so that it is frequently observed among several members of a family. Young adults may transmit it by sleeping together, as opposed to a brief sexual contact. Scabies occurs among those in all groups and socioeconomic levels. It is common disease of troops in the field under wartime conditions.

Causative Organism

The causative factor is the itch mite, Sarcoptes scabiei. The female parasite is easily visible with a magnifying glass and measures 0.33 to 0.45 millimeters in length by .25 to .33 millimeters in height. She burrows beneath the epidermis to lay her eggs, and sets up an intense irritation. The male is smaller and resides on the surface. The disease is transmitted by direct contact with infected individuals or their clothing and bedding. It is easily transmitted from person-to-person through physical contact; fomite and animal transmission which are likely to occur. Close crowding as in tenement districts, barracks, schools, and lack of personal cleanliness are predisposing causes. However, there is no clear association of Chlamydia with poor hygiene. Anyone may become infected or reinfected. Initial infections are followed by a marked resistance to subsequent reinfection.

Risk Factors

• Immunosuppressed Patients (e.g., those with HIV infection, syphilis, hematologic malignancy, other immunosuppressant use such as  chronic intake of corticosteroid),

• Individuals with severe physical disabilities, mentally retarded,

• Australian Aborigines

• People living in warm climates develop

* However, severity is related to the patient's immune status and not in geography.

Pathophysiology

Both male and female parasites live upon the skin, but the female burrows into the superficial layer of the skin to deposit their eggs. The female itch mite penetrates the stratum corneum and burrows into the skin. Within several hours after skin penetration, the itch mite lays a large number of eggs and deposits fecal materials. The larvae mature in 10 days and move to the skin surface, where the females are impregnated; then the cycle repeats itself. Delayed hypersensitivity is thought to be a major factor. Transmission of scabies is by direct contact and to limited extent from soiled sheets and undergarments freshly contaminated by infected persons.

Incubation Period

It occurs within 244 hours from the original contact, the length of time require for the itch mite to (burrow) or infect skin and lay ova. The incubation period varies, but often a long period elapses before symptoms are noted.

The diagnosis is made by identifying the itch mite. The mite is removed from the end of a burrow with a pointed scalpel blade, or the entire burrow is slices off, placed on a slide with glycerol or mineral oil, and examined under a microscope.