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human immunodeficiency virus, either of two closely related retrovirusesretrovirus,
type of RNA virus that, unlike other RNA viruses, reproduces by transcribing itself into DNA. An enzyme called reverse transcriptase allows a retrovirus's RNA to act as the template for this RNA-to-DNA transcription.
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 that invade T-helper lymphocytes and are responsible for AIDSAIDS
or 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.
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. 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. HIV-2, seen more often in western Africa, has a slower course than HIV-1. There are many strains of both types and the virus mutates rapidly, a trait that has made it especially difficult for researchers to find an effective treatment or vaccine. In many cases, a person's immune system will fight off the invasion of HIV for many years, producing billions of CD4 cells daily, always trying to keep up with the HIV's mutations, before it succumbs and permits the well-known signs of AIDS to develop.

HIV is especially lethal because it attacks the very immune system cells (variously called T4, CD4, or T-helper lymphocytes) that would ordinarily fight off such a viral infection. Receptors on these cells appear to enable the viral RNA to enter the cell. As with all retroviruses, once the RNA is inside the cell, an enzyme called reverse transcriptase allows it to act as the template for its own RNA to DNA transcription. The resultant viral DNA inserts itself into a cell's DNA and is reproduced along with the cell and its daughters. In 2012 the Food and Drug Administration approved a pill that combines two antiretroviral drugs, tenofovir and emtricitabine, for use in preventing infection with HIV, and two years later the Centers for Disease Control and Prevention called for the drug combination to be prescribed to uninfected patients who are at risk for AIDS in an effort to reduce number of new HIV infections.

The exact origin of the virus in humans is unclear. Scientists surmise that HIV-1 jumped from African chimpanzees, who harbor a similar strain of SIV (simian immunodeficiency virus), to humans via the butchering of meat or an animal bite. The first case documented in humans dates from 1959, but genetic analysis published in 2008 estimated that it originated some time between 1884 and 1924. A 2014 analysis suggested that the most widespread form of HIV-1 in humans originated in 1920s in what was then the Belgian Congo. AIDS is believed to have spread to the Caribbean in the 1960s and the United States in the early 1970s. The virus was isolated by Luc MontagnierMontagnier, Luc Antoine,
1932–, French virologist, M.D. Sorbonne, 1960. Montagnier was a researcher at the Medical Research Council at Carshalton, London (1960–63), the Institute of Virology in Glasgow, Scotland (1963–65), and the Curie Institute in Orsay,
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 of France's Pasteur Institute in 1983. It went through several name changes before the official name, human immunodeficiency virus, was agreed upon.

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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Field evaluation of the determine rapid HIV diagnostic test in Honduras and the Dominican Republic.
Unlike in other minority groups, Chung says, there is a disturbing lack of information about transgender people and HIV. "To know how to address HIV prevention as well as HIV medical services, we need to know where these communities are," she says.
"How would I break the sad news to my husband?" Though she told him that same day, he never revealed his own HIV status.
Ron Goldschmidt, M.D., cofounder of the NCCC, advised that these are some of the questions dental clinicians should consider if they think they have been exposed to HIV:
(32) However, a woman who has had malaria during pregnancy is less susceptible to malaria during subsequent pregnancies, unless the woman is also HIV infected (31).
(37) Multivariate analyses of data from the HIV Out-Patient Study (HOPS) cohort (23) indicate that the following are risk factors for lipoatrophy: exposure to and duration of thymidine analogs (particularly stavudine and zidovudine), age, CD4 T-cell count, viral load, duration of therapy in general, and White race.
Risk-based testing was particularly likely among men who were aware of HAART, men who had ever had anal intercourse without using a condom, men who had been tested anonymously, men who had asked at least one recent new sex partner about his HIV stares and men who had reduced their risks after being tested (1.3-1.8).
The group comprises Medivir AB, subsidiary Medivir UK Ltd, Medivir HIV Franchise AB and Medivir Personal AB.
(5) However, most of the studies of hormonal contraceptives and HIV have been conducted among women at high risk of HIV infection, including sex workers in Africa.
But HIV has never been just another communicable disease; it's passed on by used needles and sex, often of the taboo sort, be it between men or just outside of marital monogamy.
If they think that they might be infected with the HIV virus, 49.8% answered that they would consult with a medical specialist, 53.7% would take an HIV test at medical institutions and 35.2% would take the test at public health offices.
George Mulcaire-Jones, president and founder of Maternal Life International, who knows first-hand that condoms don't work because of his regular travels to Africa to work hands-on in the war against AIDS, says that condoms do little physically to prevent transmission of HIV and exacerbate the problem by promoting promiscuity where that behaviour is most deadly, in Asia and Africa.