Dictionary of Human Evolution and Biology

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Human Immunodeficiency Virus, a type D retrovirus (Retroviridae), one of a number of molecularly related retroviral genomes that utilize mammalian hosts. There are two common forms of the virus that cause AIDS in humans: HIV-1 and HIV-2 (a third form, HIV-O, is very rare). Since the late 1970s, the HIV-1 form has been introduced from Africa into Europe, Asia, and the Americas, and has mutated into several new variant alleles. HIV-2 was until recently still confined to Africa, but it too has begun to appear in HIV variant surveys on other continents. The original source of HIV-1 is chimpanzees, and of HIV-2 is sooty mangabeys. The outbreak of an agent such as HIV from an animal host into humans in a disturbed environment is a scenario familiar to epidemiologists; in this case researchers suspect it was due to the use of primates as bushmeat. The retrovirus contains none of the machinery required for reproduction, so replication and assembly of new viroids occurs by using the host’s molecular machinery. Infection occurs when the virus enters a host’s circulatory system and selectively attaches to the CD4 co-receptors on T cells, which it then invades. An encapsulated reverse transcriptase transcribes the viral RNA to DNA, which is inserted into host DNA by a viral integrase. Eventually, viral mRNA copies are produced by the molecular machinery of the host cell, which are then shuttled (along with host mRNAs) into the cytoplasm where all the polypeptide chains required for the complete assembly of new virions are mechanically produced by the host cell. Finally, the assembled virions erupt from the host cell; eruption lyses host CD4 (T4 helper) cells, an event that eventually compromises the host’s immune system. HIV was formerly known as HTLV-III.

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