scabies

Scabies 

Definition

Scabies is a relatively contagious infection caused by a tiny mite(Sarcoptes scabiei).

Description

Scabies is caused by a tiny insect about 0.3 mm long called a mite. When a human comes in contact with the female mite, the mite burrows under the skin, laying eggs along the line of its burrow. These eggs hatch, and the resulting offspring rise to the surface of the skin, mate, and repeat the cycle either within the skin of the original host, or within the skin of its next victim.

The intense itching almost always caused by scabies is due to a reaction within the skin to the feces of the mite. The first time someone is infected with scabies, he or she may not notice any itching for a number of weeks (four to six weeks). With subsequent infections, the itchiness will begin within hours of picking up the first mite.

Causes and symptoms

Scabies is most common among people who live in overcrowded conditions, and whose ability to practice good hygiene is limited. Scabies can be passed between people by close skin contact. Although the mites can only live away from human skin for about three days, sharing clothing or bedclothes can pass scabies among family members or close contacts. In May 2002, the Centers for Disease Control (CDC) included scabies in its updated guidelines for the treatment of sexually transmitted diseases.

The itching, or pruritus, from scabies is worse after a hot shower and at night. Burrows are seen as winding, slightly raised gray lines along the skin. The female mite may be seen at one end of the burrow, as a tiny pearl-like bump underneath the skin. Because of the intense itching, burrows may be obscured by scratch marks left by the patient. The most common locations for burrows include the sides of the fingers, between the fingers, the top of the wrists, around the elbows and armpits, around the nipples of the breasts in women, in the genitalia of men, around the waist (beltline), and on the lower part of the buttocks. Babies may have burrows on the soles of their feet, palms of their hands, and faces.

Scratching seems to serve some purpose in scabies, as the mites are apparently often inadvertently removed. Most infestations with scabies are caused by no more than 15 mites altogether.

Infestation with huge numbers of mites (on the order of thousands to millions) occurs when an individual does not scratch, or when an individual has a weakened immune system. These patients include those who live in institutions; are mentally retarded, or physically infirm; have other diseases which affect the amount of sensation they have in their skin (leprosy or syringomyelia); have leukemia or diabetes; are taking medications which lower their immune response (cancerchemotherapy, drugs given after organ transplantation); or have other diseases which lower their immune response (such as acquired immunodeficiency syndrome or AIDS). This form of scabies, with its major infestation, is referred to as crusted scabies or Norwegian scabies. Infected patients have thickened, crusty areas all over their bodies, including over the scalp. Their skin is scaly. Their fingernails may be thickened and horny.

Diagnosis

Diagnosis can be made simply by observing the characteristic burrows of the mites causing scabies. A sterilized needle can be used to explore the pearly bump at the end of a burrow, remove its contents, and place it on a slide to be examined. The mite itself may then be identified under a microscope.

Occasionally, a type of mite carried on dogs (Sarcoptes scabiei var. canis) may infect humans. These mites cannot survive for very long on humans, and so the infection is very light.

Treatment

Several types of lotions (usually containing 5% permethrin) can be applied to the body, and left on for 12-24 hours. One topical application is usually sufficient, although the scabicide may be reapplied after a week if mites remain. Preparations containing lindane are no longer recommended for treating scabies as of 2003 because of the potential for damage to the nervous system. Itching can be lessened by the use of calamine lotion or antihistamine medications.

In addition to topical medications, the doctor may prescribe oral ivermectin. Ivermectin is a drug that was originally developed for veterinary practice as a broad-spectrum antiparasite agent. Studies done in humans, however, have found that ivermectin is as safe and effective as topical medications for treating scabies. A study published in 2003 reported that ivermectin is safe for people in high-risk categories, including those with compromised immune systems.

Prognosis

The prognosis for complete recovery from scabies infestation is excellent. In patients with weak immune systems, the biggest danger is that the areas of skin involved with scabies will become secondarily infected with bacteria.

Prevention

Good hygiene is essential in the prevention of scabies. When a member of a household is diagnosed with scabies, all that person's recently-worn clothing and bedding should be washed in very hot water.

Resources

Books

Beers, Mark H., MD, and Robert Berkow, MD., editors. "Scabies (The Itch)." Section 10, Chapter 114 In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Periodicals

Burroughs, R. F., and D. M. Elston. "What's Eating You? Canine Scabies." Cutis 72 (August 2003): 107-109.

Scabies is a contagious skin infection common among people who live in overcrowded, less than ideal hygienic environments. It is caused by the infestation of female scab mites that, upon contact, burrows under the victim's skin and lays eggs along the lines of passage. Once the eggs hatch, the new mites rise to the skin's surface, mate, and repeats the infestation. Scabies can occur anywhere on the body, including the armpit, groin, buttocks, genital area, and ankles, as shown in the illustration above.

(Illustration by Electronic Illustrators Group.)

Burstein, G. R., and K. A. Workowski. "Sexually Transmitted Diseases Treatment Guidelines." Current Opinion in Pediatrics 15 (August 2003): 391-397.

Fawcett, R. S. "Ivermectin Use in Scabies." American Family Physician 68 (September 15, 2003): 1089-1092.

Santoro, A. F., M. A. Rezac, and J. B. Lee. "Current Trend in Ivermectin Usage for Scabies." Journal of Drugs in Dermatology 2 (August 2003): 397-401.

Organizations

American Academy of Dermatology (AAD). 930 East Woodfield Road, Schaumburg, IL 60173. (847) 330-0230. http://www.aad.org.

Key terms

Mite — An insect parasite belonging to the order Acarina. The organism that causes scabies is a mite.

Pruritus — An unpleasant itching sensation. Scabies is characterized by intense pruritus.

Topical — A type of medication applied to the skin or body surface.

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scabies /sca·bies/ (ska´bēz) a contagious skin disease due to the itch mite, Sarcoptes scabiei; the female bores into the stratum corneum, forming burrows (cuniculi), attended by intense itching and eczema caused by scratching.scabiet´ic

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Norwegian scabies  a rare, severe form associated with an immense number of mites, with marked scales and crusts, usually accompanied by lymphadenopathy and eosinophilia.

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sca·bies (skbz)

n.

1. A contagious skin disease caused by Sarcoptes scabiei and characterized by intense itching.

2. A similar disease in animals.

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scabies

[skā′bēz]

Etymology: L, scabere, to scratch

a contagious disease caused by Sarcoptes scabiei, the human itch mite, characterized by intense itching of the skin and excoriation from scratching. The mite, transmitted by close contact with infected humans or domestic animals, burrows into outer layers of the skin, where the female lays eggs. Two to 4 months after the first infection, sensitization to the mites and their products begins, resulting in a pruritic papular rash most common on the webs of fingers, flexor surfaces of wrists, and thighs. Secondary bacterial infection may occur. Diagnosis may be made by microscopic identification of adult mites, larvae, or eggs in scrapings of the burrows. All contacts are treated simultaneously with topical application of permethrin, crotamiton, or another scabicide. Oral antihistamines and salicylates reduce itching. It is also recommended that clothes and bedding be washed in hot water and dried in a hot dryer. A more severe form of scabies is observed in immunocompromised patients and is characterized by vesicles and thick crusts over the skin. This form is known as Norwegain scabies and is treated with Ivermectin.

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scabies (skāˑ·bēz),

n an infectious condition caused by the human itch mite
Sarcoptes scabiei and distinguished by persistent itching that creates a raw, irritated lesion. A papular, pruritic rash may develop on the thighs, flexor region of the wrist, or the webs between the fingers approximately 2 days to 4 months after the first infection. A secondary bacterial infection is a potential complication.

Scabies.

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scabies (skā´bēz),

n a contagious disease caused by
Sarcoptes scabiei, the itch mite, characterized by intense itching of the skin.

Scabies.

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scabies

infestation by mites of the genus Sarcoptes. See also sarcoptic mange.

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feline scabies

see notoedrescati.

scabies incognito

a variant of sarcoptic mange in dogs in which mites are difficult or impossible to recover in skin scrapings, presumably because of the extensive grooming and generally high level of skin hygiene that lacks only the use of a scabicide. Also there are usually only a few mites present once an immunity develops. Further infection may cause a hypersensitivity but the mites present will still be in small numbers.

Norwegian scabies

a variety characterized by immense numbers of mites and marked scaling of the skin. Seen in immunocompromised patients.

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scabies

Mite infestation Dermatology A severe form of infestation with the itch mite, Sarcoptes scabiei var hominis, which most commonly affects children, and spreads by direct physical contact with infected individuals–ergo it is often familial or institutional; it is characterized by intense itching that develops ± 1 month after the first exposure to the mite, which infers that the manifestations are due to hypersensitivity Clinical Intensely pruritic linear eruption corresponding to the tracks of the burrowing beasts; the pruritus results in excoriation and secondary pyoderma, often in the head & neck with sparing of the palmoplantar regions; while the papules and 'tracks' of the burrowing mite are most prominent on the hands and arms, the 'scabies rash' is found on the armpits, waist, buttocks, inner thigh, and ankles, sites that where S Scabiei is rarely found Diagnosis Established by dissecting organisms or eggs from mite tunnels, placing them in 20% KOH or mineral oil and examination by the LM Treatment Lindane lotion, benzene hexachloride. See Crusted scabies.

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Patient discussion about scabies.

Q. Can scabies be on the face? About a week ago, several bumps, red and itchy, appeared on my face. I have had scabies on other parts of my body and although it feels quite similar, it doesn’t really look the same. Can it be scabies? Is it other thing?

A. If you indeed have scabies on your face, it may come from two sources: either from your scalp, where it hides when you treat the rest of your body, or your pillow. First you should be sure it's scabies (have you seen a doctor?) If it's scabies, try to wash all your pillows and change them, and then treat your face.