Scabies

18 December 2021



Itch Mite

Overview

Scabies is a highly irritant contagious skin infestation caused by the mite Sarcoptes scabiei or Itch Mite. The female Itch Mite burrows tunnels in the outer layer of skin, feed, lay eggs, and causes intense itching with characteristic pimples like erythematous papular skin rash having characteristic distribution on hands and feet and body folds. Head and neck typically spared.

Signs and Symptoms

Distribution of rash in Classic Scabies in adults and infants.

In adults, classic scabies present as a pruritic, papular skin rash with excoriations. Symptoms appear due to delayed allergic skin reaction to mites, eggs and fecal pellets within 2-6 weeks with intense intractable itching and a typical erythematous papular rash and burrows, on specific body areas. Symptoms may begin within 1-4 days after exposure if a person had scabies before. In classic scabies itching and rash occur initially in finger web spaces, flexure surface of wrists and elbow, armpits, ankles, sides of feet, along the beltline, and lower buttocks sparing head and neck in adults. In Infants and small children, the scabies rash may include vesicles, pustules or nodules on the palm, soles, face, scalp, and axillary folds.

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Itching is often worse at night. Scratching may cause skin erosions and secondary bacterial infection. Signs and symptoms can be atypical, for example, in older patients itching can be worse with little rash, or in immunocompromised patients, there may be widespread non- pruritic scaling.

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Other types of scabies

Norwegian or crusted scabies

Crusted scabies is due to an impaired immune response. In immunocompromised patients such as patients with HIV or AIDS or patients using steroids or weakened immune system due to any cause, scabies is more severe. In classic scabies, there may be 10-12 mites in the skin. In crusted scabies numbers may be in millions. Thick Scaly erythematous patches often involve hands, feet, and scalp.

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Nodular scabies

More common among Infants and young children. Erythematous nodules up to 5-6 mm in addition to classic skin rash in groin, armpits, and buttocks are found. Despite adequate treatment, scabietic nodules are slow to resolve and may persist for months. The lesions may respond to topical and/or intralesional corticosteroids.

Bullous scabies

Occur more commonly among young children and older people along with classic scabies rash.

Mode of transmission

Direct skin-to-skin contact is the most common way to share the infestation. The mites can also be spread through furniture, clothes, and bedding. Indirect spread can occur more easily when a person has crusted scabies.
Facilities such as nursing homes, schools, shelters where people live in close contact with one another often infestations spread easily.

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Scabies mites are host-specific obligate parasites. They are microscopic less than 1 mm in size. The mites on domestic animals and birds can penetrate the skin and cause itching but they can not complete their life cycle in humans. Female Itch Mite lay 10-25 eggs before dying in 8 weeks. The eggs hatch in 3-4 days and moves to the surface and mature into adults after 14-17 days.

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Diagnosis

Diagnosis is by combination of history, finding typical rash, especially burrows (which look like a pencil mark) and itching that is out of proportion to physical findings and similar symptoms in other households. Burrows usually in hands or feet are pathognomonic of scabies. Burrows are Linear or wavy scaly skin tract up to 1 cm may be visible with dark papule at one end that contains the mite. Confirmation is by finding mites by using a dermatoscope or finding mites, ova, or fecal pellets on microscopic examination in burrow scrapings. Usually, mites are not found but this does not exclude scabies.

Treatment

Treatment is with topical scabicide or sometimes oral ivermectin is used.

  • 5% Permethrin is first line of treatment. Permethrin cream is applied to whole body except head and face and washed after 8-14 hours. Application is repeated after 10 days. Retreatment is unnecessary unless new lesion appear within 10 days. Permethrin is highly effective, minimally absorbed and minimally toxic. For infants and young children, permethrin should be applied on head, neck and face excluding area around eyes and mouth. Mittens on infant’ s hand can keep permethrin out of mouth.
  • 1 % Lindane lotion (Gama benzene hexa chloride) (Not recommended for children less than 2 years and in pregnancy and lactation). Lindane has a potential for neurotoxicity, especially if there is major breaks in skin such as in crusted scabies. It is applied like Permethrin for 6 hours, washed off and then treatment repeated after a week.
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  • 10 % Crotamiton cream or lotion can be applied to scabies nodules in children. The cream is applied for 24 hours, washed off and then reapplied again for another 24 hours.
  • 5-10 % precepitated sulfur in petrolatum is safe and effective for infants, pregnant or lactating women. It is applied for 24 hours for 3 days.
  • Cold bath and calamine lotion to soothe skin irritation.
  • Oral ivermectin is given to patients who do not respond to topical treatment, immunocompromised patients and for crusted scabies. For crusted scabies Ivermectin is the agent of choice. 200 ug/kg given as single dose. Ivermectin is not approved for children less than 15 kg by FDA. For infants, pregnant and lactating women Sulfur ointment is better choice than Ivermectin.

During first week after treatment itching may increase but start decreasing after a week. Oral antihistamines or corticosteroids ointment are given as itching may last 3-4 week even after treatment. Mites in skin get killed but allergy to mite products in skin may continue for a period of time and itching subsides as skin sloughs out. Treatment has to be repeated if not healed within a month.

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Infested person s’ clothing, towels, and bed linen used in previous four days should be washed in hot water (60°C) and heat dried. Things that can not be washed, sealed in a plastic bag for at least 5 days. Mites can not live away from the host for more than 3-4 days so insecticides foggers or spraying insecticides indoors is unnecessary. Family members and persons in close contact should receive treatment as well, even if they show no symptoms of infection to reduce rates of recurrence. Rooms used by those with crusted scabies require thorough cleaning. Use bleach to clean surfaces.

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