Scabies

Organism
Scabies infestation is caused by the mite Sarcoptes scabiei. Transmission is by skin-to-skin contact. Mites burrow into the skin where they lay eggs. The offspring crawl out onto the skin, and make new burrows.

The incubation period is 2-6 weeks before the onset of itching in people without previous exposure, 1-4 days after re- exposure. The period of communicability is until the mites and eggs are destroyed by treatment. Contact infectivity is high.

Clinical presentation

Any part of the body can be affected.

Symptoms

  • The main symptom, which may take 4 to 6 weeks to develop, is a generalised itch, usually worse at night or when the body is warm (e.g. after a shower).
  • The itching is due to a hypersensitivity reaction to the absorption of mite excrement into skin.

Signs

  • An itching rash on the body and limbs. Classic sites of infection are flexures, which are warmer – interdigital folds, the wrists, elbows, knees, buttocks, genital region, and under the breasts.
  • Characteristic silvery lines may be seen where the mite has burrowed, with the mite sometimes visible at the end of the burrow. However, scratching often obliterates the burrow.
  • In the genital region, particularly on the glans penis, the rash becomes papular or nodular.
  • In patients with HIV infection or others with suppressed immune function, or in the elderly, the rash is severe and crusted. These lesions team with mites, and are a significant risk to others.
Investigations
  • Scrapings, taken from the burrows with a fine needle to reveal the mite, may be examined under light microscopy.
  • Usually the rash is characteristic but can be confused with dermatitis or eczema.
Treatment
  • Patients should be advised to avoid contact with their partners or other skin-to-skin contact until they have completed treatment, and their partner and any affected household contacts have completed treatment.
  • Patients should be given topical antipruritic creams or tablets. They should be advised that, despite successful treatment, they will continue to itch for a further four weeks due to the debris from the scabies mite in the skin. This advice prevents patients over-treating themselves and, as a result, causing eczema.
  • At night, adults should:
    • wash the entire body with soap and water, and then dry
    • apply one of the treatments below, from the neck down.
  • The cream should be rubbed in well and left on for 24 hours, then washed off. The patient may require a second dose of treatment a week later.
  • Usually, advice is also given to wash all currently used underwear, nightclothes, bed linen and bath towels in hot water, and dry them well.

Standard

  • Permethrin 5 per cent cream. Leave on for 24 hours. Repeat in 7 days if necessary.

        or

  • Benzyl benzoate 25 per cent lotion. Leave on for 24 hours. Repeat in 7 days if necessary.

Most patients will continue to itch for several weeks, so symptomatic treatment for the itch can be given in the meantime:

  • crotamiton 1 per cent lotion or cream (Eurax)

        or

  • 1 per cent hydrocortisone in calamine cream twice daily.

Treatment of scabies in HIV-positive patients should be referred to a specialist.

Pregnancy

Permethrin (category B2) is safe during pregnancy.

Medicines in pregnancy.

Related links

Management of partners
An arbitrary period of two months is quoted for contacts to be notified and treated if symptomatic. All sexual, household and institutional contacts should be treated.
Follow-up

No follow-up is usually required. If new burrows appear after treatment, then the treatment should be repeated.

Always test for other STIs when sexual transmission is suspected.

Public health issues
This is not a notifiable disease.