Scabies
From Wikipedia, the free encyclopedia
| ICD-10 | B86. |
|---|---|
| ICD-9 | 133.0 |
| DiseasesDB | 11841 |
Scabies is a transmissible ectoparasite skin infection characterized by superficial burrows, intense pruritus (itching) and secondary infection. The word scabies comes from the Latin word for "scratch" (scabere).
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[edit] Etiology
Scabies is caused by the mite Sarcoptes scabiei, variety hominis, as shown by the Italian biologists Diacinto Cestoni in the 18th century. It produces intense, itchy skin rashes when the impregnated female tunnels into the stratum corneum of the skin and deposits eggs in the burrow. The larvae, which hatch in 3-10 days, move about on the skin, molt into a "nymphal" stage, and then mature into adult mites. The adult mites live 3-4 weeks in the host's skin.
The motion of the mite in and on the skin produces an intense itch which may resemble an allergic reaction in appearance. The presence of the eggs produces a massive allergic response which, in turn, produces more itching.
Scabies is transmitted readily, often throughout an entire household, by skin-to-skin contact with an infected person (e.g. bed partners, schoolmates, daycare), and thus is sometimes, although inaccurately, classed as a sexually transmitted disease. Spread by clothing, bedding, or towels is a less significant risk, though possible.
[edit] Onset
It takes approximately 4-6 weeks to develop symptoms after initial infestation. Therefore, a person may have been contagious for at least a month before being diagnosed. This means that person might have passed scabies to anyone at that time with whom they had close contact. Someone who sleeps in the same room with a person with scabies has a high possibility of having scabies as well, although they may not show symptoms.
The symptoms are caused by an allergic reaction that the body develops over time to the mites and their by-products under the skin, thus the 4-6 week "incubation" period. There are usually relatively few mites on a normal, healthy person — about 11 females in burrows. Scabies are microscopic although sometimes they are visible as a pinpoint of white. The females burrow into the skin and lay eggs there. Males roam on top of the skin, however, they can and do occasionally burrow. Both males and females surface at times, especially at night. They can be washed or scratched off (however scratching should be done with a washcloth to avoid cutting the skin as this can lead to infection), which, although not a cure, helps to keep the total population low. Also, humans create antibodies to the scabies mites which do kill some of them.
[edit] Signs, symptoms, and diagnosis
A delayed hypersensitivity (allergic) response resulting in a papular eruption (red, elevated area on skin) often occurs 30-40 days after infestation. While there may be hundreds of papules, fewer than 10 burrows are typically found. The burrow appears as a fine, wavy and slightly scaly line a few millimeters to one centimeter long. A tiny mite (0.3 to 0.4 mm) may sometimes be seen at the end of the burrow. Most burrows occur in the webs of fingers, flexing surfaces of the wrists, around elbows and armpits, the areolae of the breasts in females and on genitals of males, along the belt line, and on the lower buttocks. The face usually does not become involved in adults.
The rash may become secondarily infected; scratching the rash may break the skin and make secondary infection more likely. In persons with severely reduced immunity, such as those with HIV infection, or people being treated with immunosuppressive drugs like steroids, a widespread rash with thick scaling may result. This variety of scabies is called Norwegian scabies.
Scabies is frequently misdiagnosed as intense pruritus (itching of healthy skin) before papular eruptions form. Upon initial pruritus the burrows appear as small, barely noticeable bumps on the hands and may be slightly shiny and dark in color rather than red. Initially the itching may not exactly correlate to the location of these bumps. As the infestation progresses, these bumps become more red in color.
Generally diagnosis is made by finding burrows, which often may be difficult because they are scarce, because they are obscured by scratch marks, or by secondary dermatitis (unrelated skin irritation). If burrows are not found in the primary areas known to be affected, the entire skin surface of the body should be examined.
The suspicious area can be rubbed with ink from a fountain pen or alternately a topical tetracycline solution which will glow under a special light. The surface is then wiped off with an alcohol pad; if the person is infected with scabies, the characteristic zigzag or S pattern of the burrow across the skin will appear.
When a suspected burrow is found, diagnosis may be confirmed by microscopy of surface scrapings, which are placed on a slide in glycerol, mineral oil or immersion in oil and covered with a coverslip. Avoiding potassium hydroxide is necessary because it may dissolve fecal pellets. Positive diagnosis is made when the mite, ova, or fecal pellets are found.
[edit] Scabies in animals
Many domestic animals have their own species of Sarcoptes mites, and all are contagious to humans as zoonoses. The most frequently diagnosed form is Sarcoptic mange in dogs. In dogs and other animals, scabies produces severe itching and secondary skin infections. Affected animals often lose weight and become unthrifty.
[edit] Compromised immune systems
People with compromised immune systems may not develop antibodies to the mites and may develop crusted Norwegian scabies. In this case, many form scabs or develop very red skin especially in the elderly and the mentally handicapped where white or gray crusted areas develop with little itching and little or no red bumps and mite population numbers soar to hundreds, thousands, or millions in AIDS patients[citation needed]. These cases require additional treatment options to ensure a complete kill. Ivermectin is the treatment of choice in these patients combined with any other topical treatment.
 Scabies on the Foot |
 Scabies on the Arm |
 Scabies on the Hand |
 Scabies of the Finger |
[edit] Treatment
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The neutrality of this section is disputed. Please see the discussion on the talk page. |
[edit] Medications
Treatments basically fall into a few different categories: topical "pesticide" applications, systemic "tablet" doses which have the advantage of ensured total coverage, and the least toxic treatment is 10% sulfur ointment, a cost-effective treatment with the least long-term side-effects.Topical (surface) medications are often effective and must be applied thoroughly to all skin from the neck down, especially to areas known to be primarily affected (skin folds, hands, etc.). The topical medication of choice is 5% permethrin because it is safe for all age groups: it should be applied for eight to twelve hours (overnight is the most convenient) then washed off. A second treatment of permethrin a week later may be recommended. Multiple applications of the cream is usually required to completely rid the body of the bugs.
Lindane (hexachlorocyclohexane) creams or lotions are considered historical treatments, and should be avoided because they have been shown to have neurotoxic effects in children and infants;[citation needed] Lindane is no longer available in the UK or Australia, but is still available in the U.S.. Similarly, 5–10% sulfur ointments are considered historical.
Although the mites are rapidly killed by treatment, itching can last for up to four weeks after treatment. A single dose of ivermectin (dosing: 200 µg/kg) has been reported to cure, but is an off-label use; some authorities recommend repeating treatment at 14 days.
Additional topical treatments include 10% crotamiton (except to eyes, nose, mouth), 25% benzyl benzoate cream or lotion.
A person can be reinfected with scabies: all household contacts must be treated simultaneously, even if asymptomatic.
The following agents have been used in the treatment of scabies:
- Lindane: (Kwell®, Kwellada®). For use with patients where permethrin use is contraindicated.[1]
- Malathion: Common pesticide, nervous system toxin in high quantities, no known mutagenic or carcinogenic properties in humans have been confirmed.[2]
- Permethrin: Another pesticide, lacks carcinogenic and teratogenic testing in humans although animal tests showed no signs of carcinogenic or teratogenic effects. Toxicity may resemble allergic reactions. [3]
- Crotamiton (Eurax®): Less toxic, but less effective. Must use for roughly 3 days. [4]
- Benzyl benzoate: Less toxic, but can cause asthmatic and allergic reactions. Must use for a week on 1st, 4th, and 7th day.[citation needed]
- Ivermectin (Stromectol®): Broad spectrum anti-parasite medication. Newest scabies treatment. Safer than other alternatives and is the easiest and quickest to use. [5]
- 10% sulfur ointment: Safest treatment.[citation needed] Non-toxic. Used in pregnant women and infants under two months of age but effective in everyone if used for 7 days.[citation needed] It is available over-the-counter, and is also the cheapest treatment. May be used as often with no risk of toxicity.[citation needed] Drawbacks include: messy, stained clothes, therefore, one should not wear white sheets and T-shirts after application.[citation needed]
Steroids or corticosteroids should not be used to combat itching. These can cause a weakened immune system creating various new diseases and the worst type of scabies.[citation needed] Options include antihistamines such as cetirizine. Prescription: Doxepin (Sinequan® - oral or Zonalon® - topical).
Without a host, scabies mites survive for a few hours in the environment (the mites rapidly dry out). Therefore it is recommended, after treatment, to wash all material (such as clothes and bedding) that has been in prolonged contact with the infested person or persons in the last four days.
Approximately 300 million cases of infestation with scabies occur worldwide annually.
Scabies also occurs in dogs; see article at mange. Dog mites can easily be transferred to humans. Although mites that infect dogs are not able to complete their life cycle on humans, they can cause quite a bit of itching before they finally die. Dogs with mange should be treated to avoid continuously re-infecting humans.
Bird mites have also be noted to cause a similar disease.[1]
[edit] References
- The Merck Manual of Diagnosis and Therapy, 17th edition, 1999
- Clinician's Pocket Reference, 9th edition, 2002
- Taber's Cyclopedic Medical Dictionary, 17th edition, 1993
- United States Centers for Disease Control and Protection
- World Health Organization Essential Medicines Library
- American Social Health Association
- Chosidow O. "Scabies". New Engl J Med 354 (16): 1718–1727.
[edit] Numbered references
- ^ Kong TK, To WK (2006). "Bird-Mite Infestation". New Engl J Med 354 (16): 1728.
[edit] External links
- Morgellons-Message-Board Morgellons-scabies-Message-Board
