Scabies - Causes, Symptoms and Treatments
An age-old skin infection, scabies results from infestation with Sarcoptes scabiei var. hominis (itch mite), which provokes a sensitivity reaction. It occurs worldwide, is predisposed by overcrowding and poor hygiene, and can be endemic.
Causes of Scabies:
Mites can live their entire life cycles in the skin of humans, causing chronic infection. The female mite burrows into the skin to lay her eggs, from which larvae emerge to copulate and then reburrow under the skin.
Transmission of scabies occurs through skin or sexual contact. The adult mite can survive without a human host for only 2 or 3 days.
Signs and Symptoms of Scabies:
Typically, scabies causes itching that intensifies at night. Characteristic lesions take many forms but are usually excoriated and may appear as erythematous nodules.
Burrows are threadlike lesions approximately 3/8" long and generally occur between fingers, on flexor surfaces of the wrists, on elbows, in axillary folds, at the waistline, on nipples in females, and on genitalia in males. In infants, the burrows may appear on the head and neck.
Intense scratching can lead to severe excoriation and secondary bacterial infection. Itching may become generalized secondary to sensitization.
A drop of mineral oil placed over the burrow, followed by superficial scraping and examination of expressed material under a low-power microscope, may reveal the mite, ova, or mite feces. However, excoriation or inflammation of the burrow often makes such identification difficult.
If diagnostic tests offer no positive identification of the mite and if scabies is still suspected (for example, if close contacts of the patient also report itching), skin clearing that occurs after a therapeutic trial of a pediculicide confirms the diagnosis. Other conditions to consider include eczema, pruritus, and insect bites.
Treatment of Scabies:
Generally, treatment of scabies consists of application of a pediculicide - permethrin cream or lindane lotionin a thin layer over the entire skin surface. The pediculicide is left on for 8 to 12 hours. To make certain that all areas have been treated, this application should be repeated in approximately 1 week. Another pediculicide, crotamiton cream, may be applied on 5 consecutive nights but is not as effective. Widespread bacterial infections require systemic antibiotics.
Persistent pruritus (from mite sensitization or contact dermatitis) may develop from repeated use of pediculicides rather than from continued infection. An antipruritic emollient or topical steroid can reduce itching; intralesional steroids may resolve erythematous nodules.
Special considerations of Scabies:
1. Instruct the adult patient to apply permethrin cream or lindane lotion at bed-time from the neck down, covering the entire body. The cream or lotion should be washed off in 8 to 12 hours. Contaminated clothing and linens must be washed in hot water or dry-cleaned.
2. Tell the patient not to apply lindane lotion if skin is raw or inflamed. Advise the patient to report any skin irritation or hypersensitivity reaelion immediately, to discontinue using the drug, and to wash it off thoroughly.
3. Suggest that family members and other close contacts of the patient be checked for possible symptoms and be treated if necessary.
4. If a hospitalized patient has scabies, prevent transmission to other patients: Practice good hand-washing technique or wear gloves when touching the patient, observe wound and skin precautions for 24 hours after treatment with a pediculicide, gas autoclave blood pressure cuffs before using them on other patients, isolate linens until the patient is noninfectious, and thoroughly disinfect the patient's room after discharge.
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