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What is HIV? HIV (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. 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. The exact origin of the virus in humans is unclear. Scientists surmise that it jumped from an animal population, probably African monkeys or chimpanzees, to humans via a bite or meat. The first case documented in humans dates from 1959. Robert Gallo of the U.S. National Institutes of Health and Luc Montagnier of France’s Pasteur Institute isolated the virus independently in 1983. It went through several name changes before the official name, human immunodeficiency virus, was agreed upon. AIDS 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. The virus was isolated in both France and the United States in 1984 and was ultimately named the human immunodeficiency virus (HIV). There are two forms of the HIV virus, HIV-1 and HIV-2. The majority of cases worldwide are caused by HIV-1. In 1999 an international team of genetic scientists reported that HIV-1 can be traced to a closely related strain of virus, called simian immunodeficiency virus (SIV), that infects a subspecies of chimpanzee (Pan troglodytes) in west-central Africa. Chimpanzees are hunted for meat in this region, and it is believed the virus may have passed from the blood of chimpanzees into humans through superficial wounds.Thanks to www.infoplease.com
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