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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.


References in periodicals archive ?
A Danish team conducted this new study to learn more about how smoking affects heart attack risk in people with HIV compared with HIV-negative people, and to estimate the proportion of heart attacks that might be avoided if HIV-positive people never smoked or if smokers quit.
HIV-positive patients have different ways of interpreting and internalising HIV- and AIDS-related information whilst health professionals don't always establish the correctness and level of internationalisation of said information within the HIV-positive patient (Evian 2011).
The ban on the donation of organs from HIV-positive donors and related research was enacted as part of the Organ Transplant Amendments Act of 1988, around the time when AIDs was just becoming part of America's conscience.
The proportion of women who intended to have children was greater among HIV-negative women (68%) than among HIV-positive ART users (31%) and HIV-positive women who had never used ART (29%).
The initially seronegative spouses were monitored regularly for "seroconversion"-that is, conversion from HIV-negative to HIV-positive.
A change in bone turnover occurs in HIV-positive patients.
HIV-positive refugees usually have no families to look after them and rarely have UNHCR-registered ID cards.
Although the large gay tour operators don't currently offer vacations specifically geared toward HIV-positive men, Toto Tours (TotoTours.
For example, Anna Yoeza, a 36-year-old mother of six, tested HIV-positive while at the hospital for prenatal care.
Three papers in the August issue of the Journal of Urban Health: Bulletin of the New York Academy of Medicine find a larger number of HIV-positive men are sexually active with women than with other men, putting women at greater and increasing risk of exposure.
His second wife is also HIV-positive, he told the conference, "but we postponed having a baby until we knew how mother-to-child transmission could be prevented.