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Simian immunodeficiency virus (SIV) is a retrovirus
Retrovirus

A retrovirus is a virus with an RNA genome that replicates by using a viral reverse transcriptase enzyme to transcription its RNA into DNA in the host cell....
 that is found, in numerous strains, in primates; the specific strains infecting humans are HIV-1 and HIV-2, the viruses that cause AIDS
AIDS

Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the HIV ....
.

The origin of HIV is now generally attributed to SIV from Africa
Africa

Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km? including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area....
n primates. HIV-2 is most closely related to SIVsm, the SIV strain that primarily infects Sooty Mangabeys, while HIV-1 is closely related to the chimpanzee
Chimpanzee

Chimpanzee, sometimes colloquially known as a chimp, is the common name for the two Extant taxon species of ape in the genus Pan where the Congo River forms the boundary between the native habitat of the two species:...
 strain of SIV, designated SIVcpz.






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Simian immunodeficiency virus (SIV) is a retrovirus
Retrovirus

A retrovirus is a virus with an RNA genome that replicates by using a viral reverse transcriptase enzyme to transcription its RNA into DNA in the host cell....
 that is found, in numerous strains, in primates; the specific strains infecting humans are HIV-1 and HIV-2, the viruses that cause AIDS
AIDS

Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the HIV ....
.

The origin of HIV is now generally attributed to SIV from Africa
Africa

Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km? including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area....
n primates. HIV-2 is most closely related to SIVsm, the SIV strain that primarily infects Sooty Mangabeys, while HIV-1 is closely related to the chimpanzee
Chimpanzee

Chimpanzee, sometimes colloquially known as a chimp, is the common name for the two Extant taxon species of ape in the genus Pan where the Congo River forms the boundary between the native habitat of the two species:...
 strain of SIV, designated SIVcpz. The most likely route of transmission of HIV-1 to humans involves contact with the blood of chimps that are often hunted for bushmeat
Bushmeat

Bushmeat is the term commonly used for meat of terrestrial animal wild animals, killed for subsistence or commercial purposes throughout the humid tropics of the Americas, Asia, and Africa....
 in Africa.

SIV monkey strains are transmitted sexually and usually do not cause immunodeficiency in their natural hosts, Sooty mangabeys and African Green Monkeys
Chlorocebus

The vervet monkeys or green monkeys are medium-sized primates from the family of Old World monkeys. There are six species currently recognized, although some classify them all as a single species with numerous subspecies....
, even when the infected hosts carry large viral load
Viral load

Viral load is a measure of the severity of a virus infection, and can be calculated by estimating the amount of virus in an involved body fluid....
s. SIV strains may cause an AIDS-like immune deficiency known as SAIDS (simian acquired immunodeficiency syndrome) if they cross species boundaries. For example, SIVagm, the SIV strain from African Green Monkeys causes SAIDS in Pig-tailed macaque
Pig-tailed macaque

The pig-tailed macaques are two macaque sister species. They look almost identical and are best distinguished by their parapatric ranges:* Northern Pig-tailed Macaque, Macaca leonina ...
s. Unlike African Green Monkeys, macaques are native to Asia
Asia

Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area and, with over 4 billion people, it contains more than 60% of the world's current human population....
 and do not carry their own strain of SIV. Interestingly, yellow
Yellow Baboon

The Yellow Baboon is a baboon from the Old World monkey family.Cynocephalus literally means "dog-head" in Greek due to the shape of its muzzle and head....
 and chacma baboon
Chacma Baboon

The Chacma Baboon , also known as the Cape Baboon, is, like all other baboons, from the Old World monkey family. With a body length of up to 115 cm and a weight from 15 to 31 kg, it is among the largest and heaviest baboon species....
s, African monkeys, do not develop SAIDS when they contract SIVagm.

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 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 simian origin of HIV. Further studies indicated 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 (SIVcpz).

The monkey SIV strains do not infect humans and HIV-1 does not infect monkeys. In 2004, this tropism was partly explained by different variants of the protein TRIM5a
TRIM5-alpha

TRIM5a, also written as TRIM5alpha or TRIM5-alpha, is a protein composed of 493 amino acids that is found in the cell of most primates....
 in humans and monkeys. This intracellular protein recognizes the capsid
Capsid

A capsid is the protein shell of a virus . It consists of several oligomeric structural subunits made of protein, called protomers; at the same time the 3-dimensional morphological subunits that can be observed, which may or may not correspond to individual proteins, are called capsomeres....
 of various retroviruses and blocks their reproduction. Other proteins such as APOBEC3G
APOBEC3G

APOBEC3G is a human protein belonging to the APOBEC superfamily of proteins that interferes with the replication of HIV and other retroviruses. This family of proteins has been suggested to play an important role in innate anti-viral immunity ....
/3F
APOBEC3F

Apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like 3F, also known as APOBEC3F, is a human gene....
 may be important in restricting cross-species transmission.

SHIV, a virus created for research purposes by combining parts of the HIV and SIV genomes also exists.

While it is possible that SIV infected the first human being via sexual intercourse, authorities believe that the most likely mode of original transmission was via wounds.

The ICTVdB code of SIV is 61.0.6.5.003.

See also


  • OPV AIDS hypothesis
    OPV AIDS hypothesis

    The oral polio vaccine AIDS hypothesis argues that the AIDS pandemic originated from live polio vaccines prepared in chimpanzee tissue cultures and then administered to up to one million Africans between 1957 and 1960 in experimental mass vaccination campaigns....
  • eu-FEDS


External links

  • , including links to subspecies and sequence data, from the International Committee on Taxonomy of Viruses
    International Committee on Taxonomy of Viruses

    The International Committee on Taxonomy of Viruses is a committee which authorizes and organizes the Taxonomy classification of viruses. They have developed a universal taxonomic scheme for viruses and aim to describe all the viruses of living organisms....


  • , access to sequence data and published articles


  • Peeters et al.: , Emerging Infectious Diseases, Vol 8, No 5, May 2002. Contains a picture of the relationship among the various SIV/HIV strains.


  • BBC News article