Scabies

The commonest infestation encountered is scabies, and it is easily missed or misdiagnosed. Scabies is due to a small mite, Sarcoptes scabiei. The female mite burrows into the stratum corneum to lay

Harvest mites

Erythema chronicum migrans

Harvest mites

Spider bite (Nigeria)

Papular urticaria

Persistent papules in scabies

Papular urticaria

Persistent papules in scabies her eggs; the male dies after completing his role of fertilisation, and the developing eggs hatch into larvae within a few days. Intense itching occurs some two weeks later, during which time extensive colonisation may have occurred. The infestation is acquired only by close contact with infected people.

Diagnosis

Finding a burrow—the small (5-10 mm long) ridge, often S shaped—can be difficult as it is often obscured by excoriation from scratching. Without finding a burrow, however, the diagnosis remains uncertain. Isolation of an acarus with a needle or scalpel blade and its demonstration under the microscope convinces the most sceptical patient. Always ask whether there are others in the patient's household and if any of them are itching.

Treatment

10% sulphur in yellow soft paraffin is traditional, effective, and safe. There are several more modern treatments, including 25% benzyl benzoate emulsion, 0-5% malathion cream, 1% gamma benzene hexachloride (lindane) lotion, and 1% permethrin. In children benzyl benzoate should be diluted to 10% and used with care as toxicity results from absorption. In infants over two months old permethrin or 2-5% sulphur ointment can be used. Gamma benzene hexachloride should not be given to children under 10 years or pregnant women in the first trimester. Important points are:

(1) The patient should wash well: a hot bath was formerly advocated but it is now known that this may increase absorption through the skin.

(2) The lotion should be applied from the neck down, concentrating on affected areas and making sure that the axillae, wrists, ankles, and pubic areas are included. If there is any doubt about the thoroughness of application the process should be repeated in a few days.

(3) All contacts and members of the patient's household should be treated at the same time.

(4) Residual papules may persist for many weeks. Topical steroids can be used to relieve the itching.

(5) Secondary infection as a result of scratching may need to be treated.

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