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. However, 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.

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.

External links

• Description of SIV, including links to subspecies and sequence data, from the International Committee on Taxonomy of Viruses
• NIH Taxonomy Browser entry for SIV, access to sequence data and published articles
• Peeters et al.: "Risk to Human Health from a Plethora of Simian Immunodeficiency Viruses in Primate Bushmeat", Emerging Infectious Diseases, Vol 8, No 5, May 2002. Contains a picture of the relationship among the various SIV/HIV strains.