Click here to view next page of this article

Scabies

Human scabies is a contagious disease caused by the mite Sarcoptes scabiei var. hominis. Dogs and cats may be infested by almost identical organisms; these sometimes may be a source for human infestation. In the past, scabies was attributed to poor hygiene. Most contemporary cases, however, appear in individuals with adequate hygiene who are in close contact with numbers of individuals, such as schoolchildren. Blacks rarely acquire scabies.

Anatomic features, life cycle, and immunology

ANATOMIC FEATURES.

The adult mite is ¹ /3 mm long and has a flattened, oval body with wrinklelike, transverse corrugations and eight legs. The front two pairs of legs bear claw-shaped suckers and the two rear pairs end in long, trailing bristles. The digestive tract fills.

INFESTATION AND LIFE CYCLE.

Infestation begins when a fertilized female mite arrives on the skin surface. Within an hour, the female excavates a burrow in the stratum corneum (dead, horny layer). During the mite's 30-day life cycle, the burrow extends from several millimeters to a few centimeters in length. The burrow does not enter the underlying epidermis except in the case of hyperkeratotic Norwegian scabies, a condition in which retarded, immunosuppressed, or elderly patients develop scaly, thick skin.

Clinical manifestations.

Transmission of scabies occurs during direct skin contact with an infected person. Whether or not the mite can be acquired from infested clothing or bed linen is not known. A mite can possibly survive for days in normal home surroundings.

SYMPTOMS

The disease begins insidiously. Symptoms are minor at first and are attributed to a bite or dry skin. Scratching destroys burrows and removes mites, providing initial relief. The patient remains comfortable during the day but itches at night.

Primary lesions.

Mites are found in burrows and at the edge of vesicles.

Burrow.

The linear, curved, or S-shaped burrows are approximately as wide as #2 suture material and are 2 to 15 mm long. They are pink-white and slightly elevated. A vesicle or the mite, which may look like a black dot at one end of the burrow, often may be seen. Scratching destroys burrows, therefore they do not appear in some patients. Burrows are most likely to be found in the finger webs, wrists, sides of the hands and feet, penis, buttocks, scrotum, and the palms and soles of infants.

Distribution.

Lesions of scabies are typically found in the finger webs, wrists, extensor surfaces of the elbows and knees, sides of the hands and feet, axillary areas, buttocks, waist area, and ankle area. In men, the penis and scrotum are usually involved.

Infants.

Infants, more frequently than adults, have widespread involvement. This may occur because the diagnosis is not suspected and proper treatment is delayed while medication is given for other suspected causes of itching, such as dry skin, eczema, and infection. Infants occasionally are infested on the face and scalp, something rarely seen in adults. Vesicles are common.

The elderly.

Elderly patients may have few cutaneous lesions, but itch severely. The decreased immunity associated with advanced age may allow the mites to multiply and survive in great numbers. These patients have few cutaneous lesions other than excoriations.

Crusted (Norwegian) scabies.

The term Norwegian scabies was first used in 1848 to describe an overwhelming scabies infestation of patients with Hansen's disease. In patients with crusted scabies, lesions tend to involve hands and feet with asymptomatic crusting rather than the typical inflammatory papules and vesicles. There is thick, subungual, keratotic material and nail dystrophy.

Diagnosis.

The diagnosis is suspected when burrows are found or when a patient has typical symptoms with characteristic lesions.

Treatment and management

Permethrin.

Permethrin (Elimite cream) is a synthetic pyrethrin that demonstrates extremely low mammalian toxicity. Many clinicians feel that this is now the scabicide of choice. A large study compared 5% permethrin cream with 1% lindane lotion. Complete resolution occurred in 91% of patients treated with permethrin and in 86% of patients given lindane. Pruritis persisted in 14%.

Lindane.

Lindane is the generic name for the chemical gamma benzene hexachloride, a compound chemically similar to an agricultural pesticide also referred to as lindane. Kwell is one brand name for lindane. Generic lindane is available. Lindane is available.

Ivermectin. In one study the anthelmintic agent ivermectin (6 mg tablets), given in a single oral dose (200 mug per kilogram), was found to be an effective and safe treatment for scabies in otherwise healthy patients and in patients with HIV infection.

Sulfur. Sulfur has been used to treat scabies for more than 150 years. The pharmacist mixes 6% (5% to 10% range) precipitated sulfur in petrolatum or a cold cream base. The compound is applied to the entire body below the neck once each day.

APPLICATION TECHNIQUE FOR PERMETHRIN AND LINDANE.

The cream or lotion is applied to all skin surfaces below the neck and the face in children. Patients with relapsing scabies and the elderly should be treated from head (including the scalp) to toe. One ounce is usually adequate for adults. Reapply medicine to the hands if hands are washed. The nails should be cut short and medication applied under them vigorously with a toothbrush. A hot, soapy bath is not necessary prior to application. Moisture increases the permeability of the epidermis and increases.

Crotamiton (Eurax lotion).

A study of children with scabies showed an 89% cure rate after 4 weeks with permethrin 5% cream (Elimite) and a 60% cure rate with crotamiton cream.

Eradication program for nursing homes.

Scabies is a problem in nursing homes. The severity is greater than in an ambulatory population. The face and scalp can be involved, and multiple treatments may be necessary. The first problem is proper diagnosis. The elderly have an atypical presentation with few lesions other than excoriations, dry skin, and scaling, but they experience intense itching.

Management of complications

Eczematous inflammation and pyoderma.

Although there is little evidence that lindane is absorbed in greater quantity through inflamed skin, it seems prudent to control secondary changes prior to the application of this scabicide.

Postscabietic pruritis.

Itching usually decreases substantially 24 hours after treatment with lindane and then gradually decreases during the following week or two. Patients with persistent itching may be treated with oral antihistamines, and, if inflammation is present.

Nodular scabies.

Persistent nodular lesions, most commonly found on the scrotum, are treated with intralesional steroids (e.g., triamcinolone acetonide [Kenalog] 10 mg/ml).

Environmental management.

Intimate contacts and all family members in the same household should be treated. Clothing that has touched infected skin probably plays a minimal role in the transmission of scabies; however, it is difficult to convince patients of that fact.