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Scabies
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Scabies is a contagious ectoparasite skin infection characterized by superficial burrows, intense pruritus (itching) and secondary infection. It is caused by the mite Sarcoptes scabiei. The word scabies itself is derived from the Latin word for "scratch" (scabere). It is most likely to be found in smaller dogs.
, Itch Mite, Mange, Crusted Scabies, Norwegian Scabies, Sarcoptes scabiei, The Itch, Seven-Year Itch
ies is highly contagious and can be spread by scratching, picking up the mites under the fingernails and simply touching another person's skin.
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Encyclopedia
Scabies is a contagious ectoparasite skin infection characterized by superficial burrows, intense pruritus (itching) and secondary infection. It is caused by the mite Sarcoptes scabiei. The word scabies itself is derived from the Latin word for "scratch" (scabere). It is most likely to be found in smaller dogs.
Synonyms
Mite, Itch Mite, Mange, Crusted Scabies, Norwegian Scabies, Sarcoptes scabiei, The Itch, Seven-Year Itch
- Scabies is occasionally referred to as “lice.” However, there is no clinical relationship between scabies and lice.*
Etiology
Scabies is highly contagious and can be spread by scratching, picking up the mites under the fingernails and simply touching another person's skin. They can also be spread onto other objects like keyboards, toilets, clothing, towels and anything else that the mite may be rubbed off onto, especially if a person is heavily infested. (SEE http://www.cdc.gov/scabies/)
Scabies is caused by the mite Sarcoptes scabiei, variety hominis, as shown by the Italian biologist 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 action of the mites moving within the skin and on the skin itself 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 can be transmitted readily throughout an entire household, by skin-to-skin contact with an infected person (e.g. bed partners, schoolmates, daycare). It can be spread by clothing, bedding, or towels. Wash all clothing in very hot water and dry on high heat. Use permethrin sprays for items that cannot be laundered.
The symptoms of itching and rash are caused by an allergic reaction that the human body develops over time to the mites and their by-products under the skin. As such, there is usually a 2-6 week incubation period between infestation and presentation of symptoms. However, in individuals with prior exposure to scabies, the incubation period is much shorter: as little as 1-4 days
There are usually relatively few mites on a normal, healthy person (who is infested with scabies) — 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, although can also occasionally burrow.
History of Discovery
Scabies is an ancient disease. Based on archeological evidence from Egypt and the Middle East, scabies is estimated to date back over 2,500 years . The first recorded reference to scabies is believed to be from the Bible (Leviticus, the third book of Moses) ca. 1200 BCE. Later, the Roman philosopher Aristotle reported on “lice” that would “escape from little pimples if they are pricked” in the fourth century BCE ; scholars believe this was actually a reference to scabies.
Nevertheless, it was the Roman physician Celsus who is credited with designating the term “scabies” to the disease and describing its characteristic features . The parasitic etiology of scabies was later documented by the Italian physician Giovanni Cosimo Bonomo (1663-1969 ADE) in his famous 1687 letter, “Observations concerning the fleshworms of the human body” . With this (disputed) discovery, scabies became one of the first diseases with a known cause .
Epidemiology
Scabies is impressively democratic in its epidemiology: mites are distributed around the world, affecting all ages, races and socioeconomic classes in all different climates. However, it is more often seen in crowded and unhygienic living conditions . Globally, there is an estimated incidence of 300 million cases of scabies a year, 1 million of which occur in the United States.
Signs and Symptoms
The characteristic symptoms of scabies infection include superficial burrows, intense pruritus (itching), a generalized rash and secondary infection. Acropustulosis, or blisters and pustules on the palms and soles of the feet, are characteristic symptoms of scabies in infants.
The superficial burrows appear as short, S-shaped tracks in the skin, and are often accompanied by small, insect-type bites called nodules that may look like pimples . These burrows and nodules are often located in the crevasses of the body, such as between fingers, toes, buttocks, elbows, waist area, genital area, and under the breasts in women .
The intense itching and rash characteristic of scabies infection is caused by an allergic reaction of the body to the burrowing of the microscopic scabies mites. The rash can be found over much of the body; the associated itching is often most prevalent at night .
Secondary infection is often due to impetigo, a type of bacterial skin infection, after scratching. Cellulitis may also occur, resulting in localized swelling, redness and fever (DermNet).
In immunocompromised, malnourished, elderly or institutionalized individuals, infestation can cause a more severe form of scabies known as crusted scabies or Norwegian scabies. This syndrome is characterized by a scaly rash, slight itching and thickened crusts of skin containing thousands of mites. Norwegian scabies is the form of scabies that is hardest to treat.
In individuals never before exposed to scabies, the onset of clinical signs and symptoms is 4-6 weeks after infestation; in previously exposed individuals, onset can be as soon as 1-4 days after infestation.
Morphology
Adult scabies mites are spherical, eyeless mites with four pairs of legs. They are recognizable by their oval, ventrally flattened and dorsally convex tortoise-like body and multiple cuticular spines. Females are 0.30 to .45 mm long and 0.25 to 0.35 mm wide, and males are just over half that size.
Life Cycle
The scabies mite Sarcoptes scabiei var. hominis goes through four stages in its lifecycle: egg, larva, nymph and adult.
Upon infesting a human host, the adult female burrows into the skin, where she deposits 2-3 eggs per day. These oval eggs are 0.10mm to 0.15mm long and hatch as larvae in 3-4 days. Upon hatching, the 6-legged larvae migrate to the skin surface and then burrow into molting pouches (these are shorter and smaller than the adult burrows). After 3-4 days, the larvae molt, turning into 8-legged nymphs. This form molts a second time into slightly larger nymphs, before a final molt into adult mites. Adult mites then mate when the male penetrates the molting pouch of the female. Mating occurs only once, as that one event leaves the female fertile for the rest of her life (1-2months). The impregnated female then leaves the molting pouch in search of a suitable location for a permanent burrow. Once a site is found, the female creates her characteristic S-shaped burrow, laying eggs in the process. The female will continue lengthening her burrow and laying eggs for the duration of her life.
Diagnosis
Signs and symptoms of early scabies infestation mirror other skin diseases, including dermatitis, syphilis, allergic reactions, and other ectoparasites such as lice and fleas.
Generally diagnosis is made by finding burrows - which often may be difficult because they are scarce, and because they are obscured by scratch marks. 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. Although this sounds simple in practice, actual detection of scabies sites is very difficult - requiring the scraping of dozens of suspicious lesions down to the superficial dermis. This will result in minor bleeding in spots. Even a negative (not finding any mites) scraping will not completely rule out scabies. Sometime, the best diagnosis is by the history, physicial findings and noticing response to effective topical treatment.
Domestic animals
Many domestic animals have their own species of Sarcoptes mites. Though all can transiently affect humans, the mites that cause scabies in animals reproduce on the human body and will multiply within a few days. Humans are especially susceptible to small dogs carrying the mites. Recent outbreaks have started to reach epedemic proportions. 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. Sarcoptes is a genus of skin parasites, and part of the larger family of mites collectively known as “scab mites”; they are also related to the scab mite Psoroptes, also a mite that infests the skin of domestic animals. Sarcoptic mange affects domestic animals and similar infestations in domestic fowls causes the disease known as “scabies leg”. The effects of Sarcoptes scabiei are the most well known, causing “scabies”, or “the itch”. The adult female mite, having been fertilised, burrows into the skin, usually the hands or wrists, however other parts of the body may also be affected, and lays its eggs.
Compromised immune systems
People with compromised immune systems, such as HIV, cancer or transplant patients maybe susceptible to crusted or Norwegian scabies. In this case the scabies go unregulated by cytotoxic cells and spread over the whole body, except the face. These cases require additional treatment options for resolution. Ivermectin is a single oral treatment of choice in these patients combined with any other topical treatment.
Gallery of scabies infections
Evolution of infection
Treatment
Scabies is not curable without prescription medication. The two medication options are a prescription cream or prescription pills; the topical cream is by far the most common treatment.
Medications
Topical
- Permethrin: Another pesticide, Permethrin is classified by the US EPA as a likely human carcinogen, based on reproducible studies in which mice fed permethrin developed liver and lung tumors. Toxicity may resemble allergic reactions. Apply on skin before bedtime and leave it on for about 8 to 14 hours, then shower it off in the morning. Repeat until tube is finished or until rashes disappear (depending on physician's instructions).
- Eurax (USP Crotamiton)
- Malathion Applied for 24 hours; effective in killing both adults and eggs.
- Lindane (Kwellada): For use with patients where permethrin has failed or is contraindicated.
Lindane is FDA approved as safe and effective when used as directed for the second-line treatment for both scabies and lice. Serious side effects are rare and have almost always resulted from product misuse. Lindane is registered for use in 50 countries, with restricted-use status in 33 of these countries. The latter includes the U.S. and Canada, which support public health uses of pharmaceutical lindane but no longer allow agricultural applications. Lindane should be washed off with warm, and not hot, water to avoid absorption through the skin.
- There is some evidence that a 10% sulfur ointment in petroleum jelly applied topically is effective. It is cheap and readily available over-the-counter. It also has the advantange of being able to be used in pregnant women and infants under two months of age.
- Neem oil is deemed very effective in the treatment of scabies although only preliminary scientific proof exists which still has to be corroborated, and is recommended for those who are sensitive to permethrin, a known insecticide which might be an irritant. Also, the scabies mite has yet to become resistant to neem, so in persistent cases neem has been shown to be very effective.
- Tea tree oil in one study was more effective than commercial medications against the scabies mite in an in vitro situation.
Oral
A single dose of Ivermectin has been reported to reduce the load of scabies but another dose is required after 2 weeks for full eradication. In 1999, a small scale test comparing topically applied Lindane to orally administered Ivermectin found no statistically significant differences between the two treatments.
As Ivermectin is easily administered (not requiring a rub down of the whole body like lindane or permethrin twice per treatment), compliance is much better. Ivermectin is used in eradication programs of many parasites of both human and animal.
SIDE EFFECTS may include mild abdominal pain, nausea, vomiting, myalgia and/or arthralgia, which subside. The product is considered safe for use in children over five months of age pregnant woman
Public Health and Prevention Strategies
There is no vaccine available for scabies, nor are there any proven causative risk factors. Therefore, most strategies focus on preventing re-infection. All family and close contacts should be treated at the same time, even if asymptomatic. Cleaning of environment should occur simultaneously, as there is a risk of reinfection. Therefore it is recommended to wash and hot iron all material (such as clothes, bedding, and towels) that has been in contact with scabies infestation.
Cleaning the environment should include:
- Vacuuming floors, carpets, and rugs.
- Disinfecting floor and bathroom surfaces by mopping.
- Cleaning the shower/bath tub after each use.
- Daily washing of recently worn clothes, towels and bedding in hot water, drying in a hot dryer and steam ironing.
Itchiness during treatment
Options to combat itchiness include antihistamines such as chlorpheniramine. Prescription: Hydroxyzine (Atarax).
See also
External links
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