What is Scabies?

Scabies is a contagious, pruritic infestation of the skin caused by the human mite Sarcoptes scabiei. Persons of all ages, socioeconomic levels and races are susceptible. The condition occurs worldwide, and is not directly related to levels of hygiene.

The most distressing Symptom is pruritus, which often increases at night. Secondary bacterial infections are common, particularly in warm climates and crowded living conditions. Scabies occurs as a papular, pustular, vesicular, scaling or crusted eruption, which may mimic many other common dermatological disorders. Pruritus associated with any skin eruptions should alert the clinician to the possibility of scabies, regardless of the presenting features. Questions regarding recent contacts or other persons with similar symptoms should always form part of the patient interview.

Folds and crevices of the body are the most common sites of infestation. Under favorable conditions, the female mite burrows into the lower stratum comeum and upper epidermis. It is important to recognize that burrows may not be present, especially in warm climates. Toxic and antigenic secretions and fecal pellets from the mite are the cause of the host reaction and intense pruritus. Eruptions may not develop for a month or more after the first exposure, but recurring symptoms may begin within a day or two after a second infestation. This makes a thorough history important to ensure a correct diagnosis.

THE MOST COMMON CLUES OF SCABIES DIAGNOSIS ARE:

• Pruritus, worse at night
• Insidious onset in first-time infestations
• Bodily distribution of lesions
• Pleomorphic lesions, usually symmetrical
• Epidemiological risks or contact with other cases
• Positive microscopic finding from scrapings

Scabies Diagnosis

In infants, lesions may occur on any part of the body, although the hands, wrists and buttocks are the most common areas involved. In otherwise healthy adults, the breasts in women, and the genitalia in men are often the earliest sites of pruritus and eruptions.

Typical Scabies Lesions

• Excoriations
• Scaling
• Papules
• Burrows
• Vesicles
• Crusting
• Pustules
• Nodules

Scabies may resemble other dermatological conditions such as dermatophytosis, contact dermatitis, or psoriasis. When burrows are present, they appear as grayish-white, tortuous, threadlike elevations of the stratum comeum, at or near the end of which the female mite resides, if not previously removed by scratching. The mite is never more than a third of a millimeter in diameter, or just ,visible to the naked eye. In all cases of multiple pyoderma, scabies  should be considered as a possible initiating cause.

Commonly Involved Areas

• Hands
• Fingerwebs
• Flexor aspects of wrists
• Breasts
• Penis
• Buttocks, especially intergluteal folds
• Periumbilical area and umbilicus
• Extensor surfaces of elbows
• Outer borders of the feet
• Scalp, palms and soles in infants

High-Risk Populations

• INFANTS & CHILDREN Infants and children are very susceptible, and attack rates for both sexes is the same. Those who have the most frequent contact with infants are at greater risk, including older siblings, mothers and baby sitters. Adolescent and adult males are less likely to acquire scabies from children. The very elderly are once again equally susceptible, regardless of sex.
• NURSING HOMES & EXTENDED CARE FACILITIES Scabies is common and increasing in nursing homes and extended care facilities, where outbreaks or endemic infestations may affect half or more of the patients, when not adequately controlled. Lesions in the elderly may occur anywhere on the body, including the back. The body distribution and pleomorphic nature of scabies lesions in the elderly make diagnosis difficult.
• OTHER HIGH-RISK POPULATIONS Other high-risk populations include those forced into cramped quarters, such as refugees, boat people, and the victims of war, famine, and natural disasters. Because transmission is almost always through close physical contact, bed mates and sexual partners should also be considered at risk. Scabies in kindergarten and preschool facilities can occur and is not related to the standard of care, or cleanliness of the environment.
• TRAITS OF HUMAN SCABIES MITE Human scabies mites are not transmitted to household pets. Rarely, popular eruptions maybe acquired from pets with scabietic mange, but the mite cannot complete its life cycle in human skin and soon dies. Repeated attacks require appropriate veterinary care for the pets.
• TRAITS OF PARASITIC SCABIES MITE Mites which are parasitic on birds, rats or other mammals may occasionally cause problems in humans. These have been described as eat and run mites,” and are rarely found on the skin of the victims at the time of examination. Papular eruptions are usually noted on the exposed surfaces, particularly forearms, ankles, and neck, and burrows are absent. Management entails a careful history, investigation of the home or workplace, and removal or dis infestation of the sources, preferably by trained pest management personnel.

Patient-Induced Complications

Because of the intense itching and the fact that the condition is caused by a living mite crawling under the skin, patients require particular reassurances that their problem is not due to uncleanliness, and can be cured. They should be informed that the prescribed medication will kill the offending parasites, but the itching may continue for a week or more. Self-administered over treatment should be discouraged, and overzealous cleansing can irritate the skin and increase pruritus.

Summary

Scabies is a contagious parasitic disease which is difficult to diagnose because lesions often mimic other dermatoses. Scabies is characterized by pruritus, which is worse at night, and should be suspected whenever patients present with any intensely pruritic eruptions Commonly involved areas include skin folds or creases. The condition typically affects persons who come into close physical contact with others, and is not necessarily associated with poor hygiene or neglect. A careful history. often reveals the source of the infestation.