18 December 2021
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 feeds and lays eggs, which causes intense itching with characteristic erythematous papular skin rash having characteristic distribution on hands and feet and body folds.
Signs and Symptoms
Distribution of rash in Classic Scabies in adults and infants.
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. The itching is often worse at night. Scratching may cause skin erosions and secondary bacterial infection. In older patients itching can be worse with little rash, and in immunocompromised patients, there may be widespread non-pruritic scaling.
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.
Nodular scabies is more common among infants and young children. Erythematous nodules up to 5-6 mm in addition to classic skin rash in the groin, armpits, and buttocks are found. Nodules are slow to resolve despite adequate treatment and may persist for months. The lesions may respond to topical and/or intralesional corticosteroids.
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. Infestations spread easily in nursing homes, schools, and shelters where people live in close contact.
Scabies mites are host-specific obligate parasites. They are microscopic less than 1 mm in size. A female lay 10-25 eggs before dying in 8 weeks. The eggs hatch in 3-4 days and move to the surface and mature into adults after 14-17 days. The mites on domestic animals and birds can penetrate the skin and cause itching but they can not complete their life cycle in humans.
Diagnosis is by a 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 is 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, ova, or fecal pellets on microscopic examination in burrow scrapings. Dermoscopy is a highly sensitive method for diagnosing scabies. Mites are not found usually but this does not rule out scabies.
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Treatment is done with topical scabicide or sometimes oral Ivermectin is used.
- 5% Permethrin is the first line of treatment. Permethrin cream is applied to the whole body except the head and face and washed after 8-14 hours. Application is repeated after 10 days. Retreatment is unnecessary unless a new lesion appears within 10 days. Permethrin is highly effective, minimally absorbed, and minimally toxic. For infants and young children, Permethrin should be applied on the head, neck, and face excluding areas around the eyes and mouth. Mittens on the infant’s hand can keep Permethrin out of the 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 are major breaks in the skin such as in crusted scabies. It is applied like Permethrin for 6 hours, washed off, and then treatment repeated after a week.
- 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 % precipitated sulfur in petrolatum is safe and effective for infants and pregnant or lactating women. It is applied for 24 hours for 3 days.
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- Cold bath and calamine lotion application to soothe skin irritation.
- Oral ivermectin is given to patients who do not respond to topical treatment, immunocompromised patients, and patients having crusted scabies. For crusted scabies, Ivermectin is the agent of choice. 200 ug/kg given as a single dose. Ivermectin is not approved for children less than 15 kg by FDA. For infants, pregnant and lactating women Sulfur ointment is a better choice than Ivermectin.
During the first week after treatment itching may increase, and then start decreasing. Oral antihistamines or corticosteroid ointment are given as itching may last 3-4 weeks even after treatment. Mites in the skin get killed but allergy to mite products in the skin may continue for a period of time and itching subsides as the skin sloughs out. Treatment has to be repeated if not healed within a month.
Mites can not live away from the host for more than 3-4 days. Infested person s’ clothing, towels, and bed linen used in the 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. Spraying insecticides indoors is not necessary. Family members and persons in close contact should also receive treatment, even if they show no symptoms to reduce rates of recurrence. Rooms used by those with crusted scabies require thorough cleaning. Use bleach to clean surfaces.
Neogen Insectrin X – 32 Ounce
- Insectrin X Concentrate is a broad spectrum, multi-use insecticide that kills fast and has residual action
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- For use on livestock, animal premises, lawns and ornamentals
- Mix with water or oil for use as a spray and mix with oil for cattle backrubber use to control horn flies, face flies, horseflies, ticks and ear ticks
- Works in conjunction with Prozap bovi-rubs