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acquired immunodeficiency syndrome,fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders. It was first recognized as a disease in 1981. The virus was isolated in 1983 and was ultimately named the human immunodeficiency virus (HIVHIV,
human immunodeficiency virus, either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States.
..... Click the link for more information. ). There are two forms of the HIV virus, HIV-1 and HIV-2. The majority of cases worldwide are caused by a subgroup of HIV-1. In 1999 an international team of genetic scientists reported that the strain of HIV-1 responsible for most cases of AIDS can be traced to a closely related strain of virus, called simian immunodeficiency virus (SIV), that infects a subspecies of chimpanzee (Pan troglodytes troglodytes) in W central Africa. Chimpanzees are hunted for meat in this region, and the virus may have passed from the blood of chimpanzees into humans through superficial wounds, probably in the early 1920s. AIDS is now believed to have reached the Caribbean in the 1960s and United States in the early 1970s.
Action of the Virus
In a process still imperfectly understood, HIV infects the CD4 cells (also called T4 or T-helper cells) of the body's immune system, cells that are necessary to activate B-lymphocytes and induce the production of antibodies (see immunityimmunity,
ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
..... Click the link for more information. ). Although the body fights back, producing billions of lymphocytes daily to fight the billions of copies of the virus, the immune system is eventually overwhelmed, and the body is left vulnerable to opportunistic infections and cancers.
Signs and Symptoms
Some people develop flulike symptoms shortly after infection, but many have no symptoms. It may be a few months or many years before serious symptoms develop in adults; symptoms usually develop within the first two years of life in infants infected in the womb or at birth. Before serious symptoms occur, an infected person may experience fever, weight loss, diarrhea, fatigue, skin rashes, shingles (see herpes zosterherpes zoster,
infection of a ganglion (nerve center) with severe pain and a blisterlike eruption in the area of the nerve distribution, a condition called shingles. The causative organism is varicella zoster, a common, filtrable virus that is also known to cause chicken pox.
..... Click the link for more information. ), thrushthrush,
in medicine, infection caused by the fungus Candida albicans, manifested by white, slightly raised patches on the mucous membrane of the tongue, mouth, and throat. The mucous membrane beneath the patches is usually raw and bleeding.
..... Click the link for more information. , or memory problems. Infants may fail to develop normally.
The definition of AIDS has been refined as more knowledge has become available. In general it refers to that period in the infection when the CD4 count goes below 200 (from a normal count of 1,000) or when the characteristic opportunistic infections and cancers appear. The conditions associated with AIDS include malignancies such as Kaposi's sarcomaKaposi's sarcoma
, a usually fatal cancer that was considered rare until its appearance in AIDS patients. First described by an Austro-Hungarian physician, Moritz Kaposi, in 1872, it appears in three forms and is characterized by vascular skin tumors.
..... Click the link for more information. , non-Hodgkin's lymphomalymphoma, non-Hodgkin's,
any cancer of the lymphoid tissue (see lymphatic system) in which the Reed-Sternberg cells characteristic of Hodgkin's disease (the other category of lymphoma) are not present.
..... Click the link for more information. , primary lymphoma of the brain, and invasive carcinoma of the cervix. Opportunistic infections characteristic of or more virulent in AIDS include Pneumocystis carinii pneumoniapneumonia
, acute infection of one or both lungs that can be caused by a bacterium, usually Streptococcus pneumoniae (also called pneumococcus; see streptococcus), or by a virus, fungus, or other organism.
..... Click the link for more information. , herpes simplexherpes simplex
, an acute viral infection of the skin characterized by one or more painful, itching blisters filled with clear fluid. It is caused by either of two herpes simplex viruses: Type 1, herpes labialis,
..... Click the link for more information. , cytomegaloviruscytomegalovirus
, member of the herpesvirus family that can cause serious complications in persons with weakened immune systems and infants. A common virus, it is estimated that up to 80% of Americans carry cytomegalovirus by the time they reach adulthood.
..... Click the link for more information. , and diarrheal diseases caused by cryptosporidiumcryptosporidium
, genus of protozoans having at least four species; they are waterborne parasites that cause the disease cryptosporidiosis. One of the species appears to be responsible for most of the illnesses.
..... Click the link for more information. or isospora. In addition, hepatitishepatitis
, inflammation of the liver. There are many types of hepatitis. Causes include viruses, toxic chemicals, alcohol consumption, parasites and bacteria, and certain drugs.
..... Click the link for more information. C is prevalent in intravenous drug users and hemophiliacs with AIDS, and an estimated 4 to 5 million people who have tuberculosistuberculosis
(TB), contagious, wasting disease caused by any of several mycobacteria. The most common form of the disease is tuberculosis of the lungs (pulmonary consumption, or phthisis), but the intestines, bones and joints, the skin, and the genitourinary, lymphatic, and
..... Click the link for more information. are coinfected with HIV, each disease hastening the progression of the other. Children may experience more serious forms of common childhood ailments such as tonsillitis and conjunctivitisconjunctivitis
, inflammation or infection of the mucosal membrane that covers the eyeball and lines the eyelid, usually acute, caused by a virus or, less often, by a bacillus, an allergic reaction, or an irritating chemical.
..... Click the link for more information. . These infections conspire to cause a wide range of symptoms (coughing, diarrhea, fever and night sweats, and headaches) and may lead to extreme weight loss, blindness, hallucinations, and dementia before death occurs.
Transmission and Incidence
HIV is not transmitted by casual contact; transmission requires a direct exchange of body fluids, such as blood or blood products, breast milk, semen, or vaginal secretions, most commonly as a result of sexual activity or the sharing of needles among drug users. Such a transmission may also occur from mother to baby during pregnancy or at birth. Saliva, tears, urine, feces, and sweat do not appear to transmit the virus. Since 2010 several studies have shown that transmission of HIV is significantly reduced to individuals who take antiretroviral drugs prophylactically. In 2012 the Food and Drug Administration approved a pill that combines two antiretroviral drugs, tenofovir and emtricitabine, for use in preventing HIV infection, and in 2014 the Centers for Disease Control and Prevention called for the regimen to be prescribed to individuals at risk for infection.
By 2015 it was estimated that some 36.7 million people were infected with HIV worldwide, the great majority in Third World countries; more than 30 million had died from AIDS. The disease in sub-Saharan Africa, which has been especially hard hit, in the main has been transmitted heterosexually and has been exacerbated by civil wars and refugee problems and less restrictive local mores with regard to sex. Some 25.5 million people were infected with HIV in this region, where, in many countries, the prevalence of AIDS has lowered the life expectancy. Nonetheless, the spread of the disease had slowed somewhat during the previous decade; an estimated 3.2 million new HIV infections occurred in 2001, but only 2.1 million in 2015.
In the United States, the demographics of AIDS have changed over time. In the 1980s it was seen mainly in homosexual and bisexual men and was one of the spurs to the gay-rights movementgay-rights movement,
organized efforts to end the criminalization of homosexuality and protect the civil rights of homosexuals. While there was some organized activity on behalf of the rights of homosexuals from the mid-19th through the first half of the 20th cent.
..... Click the link for more information. , as activists lobbied for research and treatment monies and began education and prevention programs. Also in the early years, before careful screening of blood products was deemed necessary, the virus was contracted by an estimated 9,000 hemophiliacs (see hemophiliahemophilia
, genetic disease in which the clotting ability of the blood is impaired and excessive bleeding results. The disease is transmitted through females but almost invariably affects male offspring only.
..... Click the link for more information. ), and a small number of people were infected by surgical or emergency blood transfusions. Before long, however, the majority of new HIV infections were seen in drug users who contracted the disease from shared needles or unprotected sex; a large proportion of infected women were drug users or partners of drug users. Since the early 21st cent., however, the majority of new cases again have been in homosexual and bisexual men. Nearly a third of the infants born to HIV-infected women are infected with the virus. (Some of these infants test positive for AIDS only because of the mother's antibodies and later test negative.) In general, the number of new infections in the United States has diminished significantly since the mid-1980s, when they were estimated at 130,000 a year. Although annual infections increased somewhat during the late 1990s from the lows reached in early 90s, they subsequently leveled off and again began decreasing, to less than 40,000 in 2015.
Tests and Treatment
Various blood tests now are used to detect HIV. The most frequently used test for detecting antibodies to HIV-1 is enzyme immunoassay. If it indicates the presence of antibodies, the blood is more definitively tested with the Western blot method. A test that measures directly the viral genes in the blood is helpful in assessing the efficacy of treatments.
There is no cure for AIDS, but it may be treated with a number of different antiretroviral drugs, often in combination. Early treatment with retrovirals, as soon as a person tests positive for infection with HIV, has been shown in studies to reduce to the transmission of HIV. Drugs such as AZTAZT
, drug used to treat patients infected with the human immunodeficiency virus (HIV), which causes AIDS; also called azidothymidine. Originally developed in 1964 as an anticancer drug, AZT was never approved for that purpose.
..... Click the link for more information. , ddI, and 3TC, which are reverse transcriptase inhibitors, have proved effective in delaying the onset of symptoms in certain subsets of infected individuals. The addition of a protease inhibitorprotease inhibitor
, any of a class of drugs that interfere with replication of the AIDS virus (HIV), by blocking an enzyme (protease) necessary in the late stages of its reproduction.
..... Click the link for more information. , such as saquinovir, amprenavir, or atazanavir, to AZT and 3TC has proved very effective, but the drug combination does not eliminate the virus from the body. Efavirenz (Sustiva), another type of reverse transcriptase inhibitor, must be taken with protease inhibitors or older AIDS medicines. Highly active antiretroviral therapy (HAART), a combination typically of three or more anti-AIDS drugs, is now the preferred treatment. Opportunistic infections are treated with various antibiotics and antivirals, and patients with malignancies may undergo chemotherapy. These measures may prolong life or improve the quality of life, but drugs for AIDS treatment may also produce painful or debilitating side effects.
Many experimental AIDS vaccines have been developed and tested, but none has yet proved more than modestly effective, including some that underwent full-scale testing. The development of a successful vaccine against AIDS has been slowed because HIV mutates rapidly, causing it to become unrecognizable to the immune system, and because, unlike most viruses, HIV attacks and destroys essential components of the very immune system a vaccine is designed to stimulate.
Governments and the pharmaceutical industry continue to be under pressure from AIDS activists and the public in general to find a cure for AIDS. Attempts at prevention through teaching "safe sex" (i.e., the relatively safer sex accomplished by the use of condoms), sexual abstinence in high-risk situations, and the dangers to drug users of sharing needles have been impeded by those who feel that such education gives license to promiscuity and immoral behaviors.
See S. Sontag, AIDS and Its Metaphors (1989); S. Flanders, AIDS (1991); G. Corea, The Story of Women and AIDS (1992); J. Pepin, The Origins of AIDS (2011); publications of Gay Men's Health Crisis, the National Institute of Allergy and Infectious Diseases, and the Centers for Disease Control and Prevention.
, form of political and social organization typical of Western Europe from the dissolution of Charlemagne's empire to the rise of the absolute monarchies. The term feudalism is derived from the Latin feodum,
..... Click the link for more information. , type of feudal due paid by a vassal to his suzerain (overlord). Aids varied with time and place, although in English-speaking countries aids were traditionally due on the knighting of the lord's eldest son, on the marriage of the lord's eldest daughter, and for ransom of the lord from captivity. These are the three aids specified in the Magna CartaMagna Carta
or Magna Charta
[Lat., = great charter], the most famous document of British constitutional history, issued by King John at Runnymede under compulsion from the barons and the church in June, 1215.
..... Click the link for more information. (1215), which forbade the king to levy aids from the barons on occasions other than these, except by the "common counsel" of the realm. It is difficult to distinguish aids from other feudal dues such as scutagescutage
, feudal payment, usually in cash, given in lieu of actual military service due from a vassal to an overlord. It applied especially to the vassals of the king. Scutage collection increased noticeably in the later 12th cent.
..... Click the link for more information. and tallagetallage
, Fr. taille, a type of feudal tax. In its origins tallage is not clearly distinguishable from aids (a type of feudal due), and in Germany it never developed beyond an occasional "voluntary" gift from vassal to lord.
..... Click the link for more information. . The term had a much wider scope than was indicated in the Magna Carta. In general, aids fell into disuse with the decline of feudalism, although they continued nominally in most places. On the Continent, the aids often became land or justice taxes due the local lords. In France, the aids were converted later into a royal tax that continued until the French Revolution.