Scabies

Scabies (; also sometimes known as the seven-year itch) is a contagious skin infestation by the mite '' Sarcoptes scabiei''. The most common symptoms are severe itchiness and a pimple-like rash. Occasionally, tiny burrows may appear on the skin. In a first-ever infection, the infected person usually develops symptoms within two to six weeks. During a second infection, symptoms may begin within 24 hours. These symptoms can be present across most of the body or just certain areas such as the wrists, between fingers, or along the waistline. The head may be affected, but this is typically only in young children. The itch is often worse at night. Scratching may cause skin breakdown and an additional bacterial infection in the skin.

Scabies is caused by infection with the female mite '' Sarcoptes scabiei ''var.'' hominis'', an ectoparasite. The mites burrow into the skin to live and deposit eggs. The symptoms of scabies are due to an allergic reaction to the mites. Often, only between 10 and 15 mites are involved in an infection. Scabies is most often spread during a relatively long period of direct skin contact with an infected person (at least 10 minutes) such as that which may occur during sex or living together. Spread of the disease may occur even if the person has not developed symptoms yet. Crowded living conditions, such as those found in child-care facilities, group homes, and prisons, increase the risk of spread. Areas with a lack of access to water also have higher rates of disease. Crusted scabies is a more severe form of the disease. It typically only occurs in those with a poor immune system and people may have millions of mites, making them much more contagious. In these cases, spread of infection may occur during brief contact or by contaminated objects. The mite is very small and at the limit of detection with the human eye. It is not readily obvious; factors that aid in detection are good lighting, magnification, and knowing what to look for. Diagnosis is based either on detecting the mite (confirmed scabies), detecting typical lesions in a typical distribution with typical historical features (clinical scabies), or detecting atypical lesions or atypical distribution of lesions with only some historical features present (suspected scabies).

Several medications are available to treat those infected, such as ivermectin or permethrin, crotamiton, and lindane creams. Sexual contacts within the last month and people who live in the same house should also be treated at the same time. Bedding and clothing used in the last three days should be washed in hot water and dried in a hot dryer. As the mite does not live for more than three days away from human skin, more washing is not needed. Symptoms may continue for two to four weeks following treatment. If after this time symptoms continue, retreatment may be needed.

Scabies is one of the three most common skin disorders in children, along with ringworm and bacterial skin infections. As of 2015, it affects about 204 million people (2.8% of the world population). It is equally common in both sexes. The young and the old are more commonly affected. It also occurs more commonly in the developing world and tropical climates. The word scabies is from '' la, scabere'', 'to scratch'. Other animals do not spread human scabies. Infection in other animals is typically caused by slightly different but related mites and is known as sarcoptic mange.

Signs and symptoms

The characteristic symptoms of a scabies infection include intense itching and superficial burrows. Because the host develops the symptoms as a reaction to the mites' presence over time, typically a delay of four to six weeks occurs between the onset of infestation and the onset of itching. Similarly, symptoms often persist for one to several weeks after successful eradication of the mites. As noted, those re-exposed to scabies after successful treatment may exhibit symptoms of the new infestation in a much shorter period—as little as one to four days.

Itching

In the classic scenario, the itch is made worse by warmth, and is usually experienced as being worse at night, possibly because distractions are fewer. As a symptom, it is less common in the elderly.

Rash

The superficial burrows of scabies usually occur in the area of the finger webs, feet, ventral wrists, elbows, back, buttocks, and external genitals. Except in infants and the immunosuppressed, infection generally does not occur in the skin of the face or scalp. The burrows are created by excavation of the adult mite in the epidermis. Acropustulosis, or blisters and pustules on the palms and soles of the feet, are characteristic symptoms of scabies in infants.

File:Acarodermatitis Fuß.jpg, Scabies of the foot
File:Acarodermatitis Arm.jpg, Scabies of the arm
File:Acarodermatitis Hand.jpg, Scabies of the hand
File:Acarodermatitis Finger.jpg, Scabies of the finger

In most people, the trails of the burrowing mites are linear or S-shaped tracks in the skin, often accompanied by rows of small, pimple-like mosquito or insect bites. These signs are often found in crevices of the body, such as on the webs of fingers and toes, around the genital area, in stomach folds of the skin, and under the breasts.

Symptoms typically appear two to six weeks after infestation for individuals never before exposed to scabies. For those having been previously exposed, the symptoms can appear within several days after infestation. However, symptoms may appear after several months or years.

Crusted scabies

The elderly, disabled, and people with impaired immune systems, such as those with HIV/AIDS, cancer, or those on immunosuppressive medications, are susceptible to crusted scabies (also called Norwegian scabies). On those with weaker immune systems, the host becomes a more fertile breeding ground for the mites, which spread over the host's body, except the face. The mites in crusted scabies are not more virulent than in noncrusted scabies; however, they are much more numerous (up to two million). People with crusted scabies exhibit scaly rashes, slight itching, and thick crusts of skin that contain large numbers of scabies mites. For this reason, persons with crusted scabies are more contagious to others than those with typical scabies. Such areas make eradication of mites particularly difficult, as the crusts protect the mites from topical miticides/scabicides, necessitating prolonged treatment of these areas.

Cause

Scabies mite

In the 18th century, Italian biologists Giovanni Cosimo Bonomo and Diacinto Cestoni (1637–1718) described the mite now called '' Sarcoptes scabiei'', variety ''hominis'', as the cause of scabies. ''Sarcoptes'' is a genus of skin parasites and part of the larger family of mites collectively known as scab mites. These organisms have eight legs as adults, and are placed in the same phylogenetic class (Arachnida) as spiders and ticks.

''S. scabiei'' mites are under 0.5 mm in size, but are sometimes visible as pinpoints of white. Gravid females tunnel into the dead, outermost layer (stratum corneum) of a host's skin and deposit eggs in the shallow burrows. The eggs hatch into larvae in three to ten days. These young mites move about on the skin and molt into a " nymphal" stage, before maturing as adults, which live three to four weeks in the host's skin. Males roam on top of the skin, occasionally burrowing into the skin. In general, the total number of adult mites infesting a healthy hygienic person with noncrusted scabies is small, about 11 females in burrows, on average.

The movement of mites within and on the skin produces an intense itch, which has the characteristics of a delayed cell-mediated inflammatory response to allergens. IgE antibodies are present in the serum and the site of infection, which react to multiple protein allergens in the body of the mite. Some of these cross-react to allergens from house dust mites. Immediate antibody-mediated allergic reactions (wheals) have been elicited in infected persons, but not in healthy persons; immediate hypersensitivity of this type is thought to explain the observed far more rapid allergic skin response to reinfection seen in persons having been previously infected (especially having been infected within the previous year or two).

Transmission

Scabies is contagious and can be contracted through prolonged physical contact with an infested person. This includes sexual intercourse, although a majority of cases are acquired through other forms of skin-to-skin conta