Get to know STD: Scabies

Other skin disease that is grouped into a sexually transmitted disease (STD) is Scabies. This time the learning series about STD (get to know STD) will discuss about Scabies. All the material below is quoted from Wikipedia entirely. Happy reading!

Sarcoptes Scabiei (Source: Wikipedia)

Scabies is an ancient disease. Archeological evidence from Egypt and the Middle East suggests scabies was present as early as 494 BC. The first recorded reference to scabies is believed to be from the Bible (Leviticus, the third book of Moses) circa 1200 BC. Later, in the fourth century BC, the ancient Greek philosopher Aristotle reported on "lice" that "escape from little pimples if they are pricked" scholars believe this was actually a reference to scabies.

Nevertheless, Greek physician Celsus is credited with naming the disease "scabies" and describing its characteristic features. The parasitic etiology of scabies was later documented by the Italian physician Giovanni Cosimo Bonomo (1663–99 AD) in his famous 1687 letter, "Observations concerning the fleshworms of the human body". With this discovery, scabies became one of the first diseases with a known cause.

Scabies (from Latin: scabere, "to scratch"), also called Norwegian scabies or colloquially the seven-year itch, is a contagious skin infection caused by the mite Sarcoptes scabiei. The mite is a tiny and usually not directly visible parasite which burrows under the host's skin, causing intense allergic itching. The infection in animals other than humans is caused by a different but related mite species, and is called sarcoptic mange.

Scabies is classified by the World Health Organization as a water-related disease. The disease may be transmitted from objects, but is most often transmitted by direct skin-to-skin contact, with a higher risk with prolonged contact. Initial infections require four to six weeks to become symptomatic. Reinfection, however, may manifest symptoms within as few as 24 hours. Because the symptoms are allergic, their delay in onset is often mirrored by a significant delay in relief after the parasites have been eradicated. Crusted scabies, formerly known as Norwegian scabies, is a more severe form of the infection often associated with immunosuppression.

Norwegian Scabies in HIV patient, need 6 months from first itch to be like this (Source: Wikipedia)

The characteristic symptoms of a scabies infection include intense itching and superficial burrows. The burrow tracks are often linear, to the point that a neat "line" of four or more closely placed and equally developed mosquito-like "bites" is almost diagnostic of the disease. In the classic scenario, the itch is made worse by warmth, and is usually experienced as being worse at night, possibly because there are fewer distractions. As a symptom, it is less common in the elderly.

The superficial burrows of scabies usually occur in the area of the hands, feet, 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.

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, and under the breasts of women.

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, it is not unknown for symptoms to appear after several months or years. Acropustulosis, or blisters and pustules on the palms and soles of the feet, are characteristic symptoms of scabies in infants.

The elderly and people with an impaired immune system, such as HIV, cancer, or those on immunosuppressive medications, are susceptible to crusted scabies (formerly 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. Sufferers of crusted scabies exhibit scaly rashes, slight itching, and thick crusts of skin that contain thousands of mites. Such areas make eradication of mites particularly difficult, as the crusts protect the mites from topical miticides, necessitating prolonged treatment of these areas.

Scabies at inguinal area on male (Source: www.std.about.com)

The symptoms are caused by an allergic reaction of the host's body to mite proteins, though exactly which proteins remains a topic of study. The mite proteins are also present from the gut, in mite feces, which are deposited under the skin. The allergic reaction is both of the delayed (cell-mediated) and immediate (antibody-mediated) type, and involves IgE (antibodies, it is presumed, mediate the very rapid symptoms on reinfection). The allergy-type symptoms (itching) continue for some days, and even several weeks, after all mites are killed. New lesions may appear for a few days after mites are eradicated. Nodular lesions from scabies may continue to be symptomatic for weeks after the mites have been killed.

Scabies may be diagnosed clinically in geographical areas where it is common when diffuse itching presents along with either lesions in two typical spots or there is itchiness of another household member. The classical sign of scabies is the burrows made by the mites within the skin. To detect the burrow, the suspected area is rubbed with ink from a fountain pen or a topical tetracycline solution, which glows under a special light. The skin is then wiped with an alcohol pad. If the person is infected with scabies, the characteristic zigzag or S pattern of the burrow will appear across the skin; however, interpreting this test may be difficult, as the burrows are scarce and may be obscured by scratch marks. A definitive diagnosis is made by finding either the scabies mites or their eggs and fecal pellets. Searches for these signs involve either scraping a suspected area, mounting the sample in potassium hydroxide and examining it under a microscope, or using dermoscopy to examine the skin directly.

Sites of Scabies (Source: Wikipedia)

Symptoms of early scabies infestation mirror other skin diseases, including dermatitis, syphilis, various urticaria-related syndromes, allergic reactions, and other ectoparasites such as lice and fleas.

Mass treatment programs that use topical permethrin or oral ivermectin have been effective in reducing the prevalence of scabies in a number of populations. No vaccine is available for scabies. The simultaneous treatment of all close contacts is recommended, even if they show no symptoms of infection (asymptomatic), to reduce rates of recurrence. Asymptomatic infection is relatively common. Since mites can only survive for two to three days without a host, objects in the environment pose little risk of transmission except in the case of crusted scabies, thus cleaning is of little importance. Rooms used by those with crusted scabies require thorough cleaning.

A number of medications are effective in treating scabies; however, treatment must often involve the entire household or community to prevent reinfection. Options to improve itchiness include antihistamines.

Permethrin

Permethrin is the most effective treatment for scabies, and is the treatment of choice. It is applied from the neck down, usually before bedtime, and left on for about eight to 14 hours, then showered off in the morning. One application is normally sufficient for mild infections. For moderate to severe cases, another dose is applied seven to 14 days later. Permethrin causes slight irritation of the skin, but the sensation is tolerable. The medication, however, is the most costly of topical treatments.

Ivermectin

Ivermectin is an oral medication shown by many clinical studies to be effective in eradicating scabies, often in a single dose. It is the treatment of choice for crusted scabies, and is often used in combination with a topical agent. It has not been tested on infants and is not recommended for children under six years of age.

Topical ivermectin preparations have been found to be effective for scabies in adults, and are attractive due to their low cost, ease of preparation, and low toxicity. It has also been useful for sarcoptic mange (the veterinary analog of human scabies).

Scabies is one of the three most common skin disorders in children, along with tinea and pyoderma. As of 2010 it affects approximately 100 million people (1.5% of the population) and is equally common in both genders. The mites are distributed around the world and equally infect all ages, races, and socioeconomic classes in different climates. Scabies is more often seen in crowded areas with unhygienic living conditions. Globally as of 2009, an estimated 300 million cases of scabies occur each year, although various parties claim the figure is either over- or underestimated. About 1–10% of the global population is estimated to be infected with scabies, but in certain populations, the infection rate may be as high as 50–80%.