Clinical Features:
When a person is infested with scabies mites for the first time, symptoms may not appear for up to two months after becoming infested; however, an infested person can still transmit scabies during this time.  If a person has had scabies before, they become sensitized to mites and symptoms generally occur much sooner, within 1 to 4 days.  Mites burrowing under the skin cause a rash, which is most frequently found on the hands, particularly the webbing between the fingers; the folds of the wrist, elbow or knee; the penis; the breast; and/or the shoulder blades.  Except in crusted (Norwegian) scabies, burrows and mites may be as few as 10-15 in number and can be difficult to find.  A papular "scabies rash" may be seen in skin areas such as the buttocks, scapular region and abdomen, where female mites are absent; this may be a result of sensitization from a previous infection.  Severe itching, especially at night and frequently over much of the body, including areas where mites are undetectable, is the most-common symptom of scabies.  A more severe form of scabies that is more common among persons who are immunocompromised, elderly, or institutionalized is called crusted (Norwegian) scabies and is characterized by vesicles and formation of thick crusts over the skin, accompanied by abundant mites but only slight itching.  Complications due to infestation are usually caused by secondary bacterial infections.

Laboratory Diagnosis:
Most diagnoses of scabies infestation are made based upon the appearance and distribution of the rash and the presence of burrows.  Whenever possible scabies should be confirmed by isolating the mites, ova or feces in a skin scraping.  Scrapings should be made at the burrows, especially on the hands between the fingers and the folds of the wrist.  Alternatively, mites can be extracted from a burrow by gently pricking open the burrow with a needle and working it toward the end where the mite is living.  The extracted mite then can be identified by microscopy.

Diagnostic findings

• Microscopy

Treatment:
Several lotions or creams to treat human scabies are available by prescription only.  The current treatment of choice is the topical use of permethrin cream (5%).  Crotamiton and ivermectin* are alternative drugs.  If a topical preparation is used, a second treatment with the same product may be necessary if itching continues more than 2-4 weeks or if new burrows or rash continue to appear.  Ivermectin* is taken orally and has been reported effective for treating crusted scabies in immunocompromised persons; a second dose is taken two weeks later.  Although FDA approved for the treatment of scabies, lindane lotion (1.0 %) is not recommended as a first-line therapy; its use should be restricted to patients who have failed treatment with, or cannot tolerate, other medications that pose less risk and for whom lindane is not contraindicated.  All clothes, bedding, and towels used by the infested person during the 3 days before treatment should be washed in hot water, and dried in a hot dryer.  For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

* This drug is approved by the FDA, but considered investigational for this purpose.