Simian immunodeficiency virus (SIV) is a retrovirus that is found, in numerous strains, in primates; the specific strains infecting humans are HIV-1 and HIV-2, the viruses that cause AIDS. Viruses can be classified in several ways, such as by their geometry, by whether they have envelopes, by the identity of the host organism they can infect, by mode of transmission, or by the type of disease they cause. ... ss-RNA RT is the single stranded Ribonucleic acid genome that is present in the HIV virus. ... Genera Alpharetrovirus Betaretrovirus Gammaretrovirus Deltaretrovirus Epsilonretrovirus Lentivirus Spumavirus A retrovirus is a virus which has a genome consisting of two identical plus sense RNA molecules. ... // Comments A lentivirus is a genus of slow viruses of the retroviridae family, characterized by long incubation period. ... Genera Alpharetrovirus Betaretrovirus Gammaretrovirus Deltaretrovirus Epsilonretrovirus Lentivirus Spumavirus A retrovirus is any virus belonging to the viral family Retroviridae. ... For the ecclesiastical use of this term, see primate (religion) Families 13, See classification A primate is any member of the biological order Primates, the group that contains all lemurs, monkeys, and apes, including humans. ... Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... The human immunodeficiency virus (HIV) is a frequently mutating retrovirus that attacks the human immune system and which has been shown to cause acquired immune deficiency syndrome (AIDS). ... The human immunodeficiency virus (HIV) is a frequently mutating retrovirus that attacks the human immune system and which has been shown to cause acquired immune deficiency syndrome (AIDS). ... Acquired Immunodeficiency Syndrome or Acquired Immune Deficiency Syndrome (AIDS or Aids) is a collection of symptoms and infections in humans resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV). ...

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 (SMs]. HIV-1 is closely related to the chimpanzee strain of SIV, designated SIV-cpz. The most likely route of transmission of HIV-1 to humans involves contact with the blood of chimps that are often hunted for bushmeat in Africa. A world map showing the continent of Africa. ... Binomial name Cercocebus atys (Audebert, 1797) The Sooty Mangabey (Cercocebus atys), also called the White-collared Mangabey, is an Old World monkey of Guinea Bissau, Gabon, and Cameroon. ... Type Species Simia troglodytes Blumenbach, 1775 Species Pan troglodytes Pan paniscus Chimpanzee, often shortened to chimp, is the common name for the two extant species in the genus Pan. ...

SIV monkey strains are transmitted sexually and usually do not cause AIDS in their natural hosts, SMs and African Green Monkeys(AGMs). Scientists suggest that this lack of response is evidence that SMs and AGMs have evolved together for a long time. One potential explanation for this unusual induction of tolerance is that SIV successfully incorporates itself into a system that protects the gametes and the developing monkey in utero from potential immune responses during the very early stages of pregnancy. This model is known as the eutherian fetoembryonic defense system (eu-FEDS) hypothesis. Evidence in favor of this paradigm is that the very mild immune response that AGMs and SMs mount against SIV closely mirrors the maternal immune response to the developing eutherian. Type Species Simia aethiops Linnaeus, 1766 Species Chlorocebus sabaceus Chlorocebus aethiops Chlorocebus djamdjamensis Chlorocebus tantalus Chlorocebus pygerythrus Chlorocebus cynosuros The vervet monkeys or green monkeys are medium-sized primates from the family of Old World monkeys. ... The Eutherian Fetoembryonic Defense System, also known by the acronym eu-FEDS is a hypothetical model describing a specific type of immunological tolerance that occurs during reproduction in mammals[1] Eutherians are members of the taxon Eutheria, which encompasses all mammals with a true placenta. ... Eutheria is a taxon (specifically, an infraclass) nearly synonymous with Placentalia, containing the placental mammals and the nearest ancestors of placental mammals (which are known only from the fossil record). ...

Immunological studies have shown that AGMs and SMs infected with SIV carry large viral loads and display similar levels of infection and subsequent apoptosis of CD4+ T cells observed in human patients infected with HIV-1. However, these natural hosts do not progress to AIDS. Instead, this weak immune response against SIV in AGMs and SMs appears to spare them from the chronic immunopathologies observed in humans and non-natural (heterologous) host species. These immunopathologies are of course almost always fatal if not treated.

SIV strains may cause an AIDS-like immune deficiency known as SAIDS (Simian AIDS) if they cross species boundaries. For example, SIV-agm, the SIV strain from AGMs causes SAIDS in Rhesus Macaques. Unlike AGMs, Rhesus monkeys are native to Asia and do not carry their own strain of SIV. Binomial name Macaca mulatta Zimmermann, 1780 The Rhesus Macaque (Macaca mulatta), often called the Rhesus Monkey, is one of the best known species of Old World monkeys. ... World map showing the location of Asia. ...

SIV was first discovered in 1985, in captive Rhesus macaques suffering from SAIDS. This observation was made 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 studies indicated that HIV-2 is derived from the SIVsm strain found in SMs whereas HIV-1, the predominant virus found in humans, is derived from SIV strains infecting chimpanzees (SIV-cpz). 1985 (MCMLXXXV) was a common year starting on Tuesday of the Gregorian calendar. ...

The monkey SIV strains do not infect humans and HIV-1 does not infect monkeys. In 2004, this tropism 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. 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... TRIM5α (also written as TRIM5alpha or TRIM5-alpha) is a protein that is found in the cells of many mammals and fends off various retrovirus infections. ... The outer shell of a virus is called the capsid. ...

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. Look up chimera, Chimaera in Wiktionary, the free dictionary. ...

The Virus Code of SIV is 61.0.6.5.003.

See also

• OPV AIDS hypothesis
• eu-FEDS

According to the oral polio vaccine (OPV) AIDS hypothesis, the AIDS pandemic originated from live polio vaccines prepared in chimpanzee tissue cultures (at least some of which were almost certainly contaminated with chimpanzee SIV) which were administered to up to one million Africans between 1957 and 1960. ... The Eutherian Fetoembryonic Defense System, also known by the acronym eu-FEDS is a hypothetical model describing a specific type of immunological tolerance that occurs during reproduction in mammals[1] Eutherians are members of the taxon Eutheria, which encompasses all mammals with a true placenta. ...

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.

• "HIV origin 'found in wild chimps'" BBC News article