Simian immunodeficiency virus

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? Simian immunodeficiency virus Template:Taxobox begin placement virus Template:Taxobox group vi entry
Family:	Retroviridae
Genus:	Lentivirus
Species:	Simian immunodeficiency virus

|} Simian immunodeficiency virus (SIV) is a retrovirus that is found, in numerous strains, in primates; the strains infecting humans are HIV-1 and HIV-2, the viruses that cause AIDS.

The origin of HIV is now generally attributed to SIV from African primates. HIV-2 is most closely related to SIV-sm, the SIV strain from Sooty Mangabey. HIV-1 is closely related to the chimpanzee strain of SIV, SIV-cpz. The most likely route of transmission from monkeys to humans involves the contact with the blood of hunted animals.

SIV monkey strains are transmitted sexually and usually do not cause disease in their natural hosts. Scientists take this as evidence that host and virus have evolved together for a long time. Immulogical studies have shown that although natural hosts for SIV can carry large viral loads, similar to those seen in humans with advanced AIDS, the natural hosts do not progress to AIDS. Instead, the lack of a strong immune response in natural hosts such as the Sooty mangabey monkey appears to spare them from the chronic immune response and subsequent immunopathogenesis observed in humans and non-natural host species. SIV strains may cause an AIDS like immune deficiency known as SAIDS (Simian Acquired Immunodeficiency Syndrome) if they cross species boundaries. For example, SIV-agm, the SIV strain from African Green Monkeys, causes SAIDS in Rhesus Macaques (the latter are native to Asia and don't carry their own strain of SIV).

SIV was first discovered in 1985, in captive Rhesus Macaques suffering from SAIDS. This was shortly after HIV-1 had been isolated as the cause of AIDS, and it led to the discovery of the HIV-2 strains in West Africa that same year. HIV-2 was more similar to the then-known SIV strains than to HIV-1, suggesting for the first time the primate origin of HIV. Further work illustrated that HIV-2 is derived from the SIVsm strain found in Sooty mangabeys whereas HIV-1, the predominant virus found in humans, is derived from SIV strains infecting chimpanzees.

The monkey SIV strains do not infect humans and HIV-1 does not infect monkeys. In 2004, this was explained by different variants of the protein TRIM5α in humans and monkeys. This intracellular protein recognizes the capsid of various retroviruses and blocks their reproduction.

To better study HIV/AIDS in animal models, researchers have created various HIV-SIV chimeras, viruses whose genome partly comes from HIV and partly from SIV. These are often referred to as SHIV.

The Virus Code of SIV is 61.0.6.5.003.

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