Simian immunodeficiency virus
|Simian immunodeficiency virus|
|Group:||Group VI (ssRNA-RT)|
|Species:||Simian immunodeficiency virus|
Simian immunodeficiency viruses (SIVs) are retroviruses able to infect at least 45 species of African non-human primates. Based on analysis of strains found in four species of monkeys from Bioko Island, which was isolated from the mainland by rising sea levels about 11,000 years ago, it has been concluded that SIV has been present in monkeys and apes for at least 32,000 years, and probably much longer.
Virus strains from two of these primate species, SIVsmm in sooty mangabeys and SIVcpz in chimpanzees, are believed to have crossed the species barrier into humans, resulting in HIV-2 and HIV-1, respectively. 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.
Unlike HIV-1 and HIV-2 infections in humans, SIV infections in their natural hosts appear in many cases to be non-pathogenic. Extensive studies in sooty mangabeys have established that SIVsmm infection does not cause any disease in these animals, despite high levels of circulating virus. However, if this virus infects an Asian or Indian rhesus macaque, the animal will develop simian AIDS (SAIDS). A recent study of SIVcpz in wild living chimpanzees suggests that infected chimpanzees experience an AIDS-like illness similar to HIV-1 infected humans. The later stages of SIV infection turn into SAIDS, much as HIV infection turns into AIDS.
Immunodeficiency resembling human AIDS was reported in captive monkeys in the United States beginning in 1983. SIV was isolated in 1985 from some of these animals, captive rhesus macaques suffering from simian AIDS (SAIDS). The discovery of SIV was made shortly after HIV-1 had been isolated as the cause of AIDS and led to the discovery of HIV-2 strains in West Africa. 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 SIVsmm strain found in sooty mangabeys, whereas HIV-1, the predominant virus found in humans, is derived from SIV strains infecting chimpanzees (SIVcpz).
Differences in species specificity of SIV and related retroviruses may be partly explained by variants of the protein TRIM5α in humans and non-human primate species. This intracellular protein recognizes the capsid of various retroviruses and blocks their reproduction. Other proteins such as APOBEC3G/3F may also be important in restricting cross-species transmission.
SHIV, a virus combining parts of the HIV and SIV genomes, was created for various research purposes, including analyzing how different parts of the virus respond to different antimicrobial drugs and vaccines.
Beatrice Hahn of the University of Pennsylvania recently led a team of researchers to find that chimpanzees do die from simian AIDS in the wild and that the AIDS outbreak in Africa has contributed to the decline of chimpanzee populations. Testing wild chimpanzees, researchers detected organ and tissue damage similar to late-stage human AIDS. The infected chimpanzees had a 10 to 16 times greater risk of dying than uninfected ones; infected females were less likely to give birth, could pass the virus to their infants, and had a higher infant mortality rate than uninfected females.
In 2010, researchers reported that SIV had infected monkeys in Bioko for at least 32,000 years. Based on molecular clock analyses of sequences, it was previously thought by many that SIV infection in monkeys had happened over the past few hundred years. Scientists estimated that it would take a similar amount of time before humans would adapt naturally to HIV infection in the way monkeys in Africa have adapted to SIV and not suffer any harm from the infection.
In 2012, researchers reported that initial infection of Rhesus monkeys by neutralization-resistant SIV strains could be partially prevented through use of an anti-SIVSME543 vaccine obligately including Env protein antigens.
In 2013, a study by a group of authors reported on successful testing of a vaccine containing SIV protein-expressing rhesus cytomegalovirus vector. Approximately 50% of vaccinated rhesus macaques manifested durable, aviraemic control of infection with the highly pathogenic strain SIVmac239.
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In a discovery that sheds new light on the history of AIDS, scientists have found evidence that the ancestor to the virus that causes the disease has been in monkeys and apes for at least 32,000 years — not just a few hundred years, as had been previously thought. ... That means humans have presumably been exposed many times to S.I.V., the simian immunodeficiency virus, because people have been hunting monkeys for millenniums, risking infection every time they butcher one for food.
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- Chimpanzees Do Die From Simian AIDS, Study Finds by Lawrence K. Altman Chimpanzees Do Die from Simian AIDS, Study Finds
- Jonathan L. Heeney; Angus G. Dalgleish; Robin A. Weiss (July 2006). "Origins of HIV and the evolution of resistance to AIDS" (PDF). Science 313 (5786): 462–466. Bibcode:2006Sci...313..462H. doi:10.1126/science.1123016. PMID 16873637.
- ICTV database entry: 188.8.131.52.003
- McNeil Jr, Donald (17 September 2010). "Precursor to H.I.V. Was in Monkeys for Millenniums". The New York Times. Retrieved 17 September 2010.
- "HIV precursor in monkeys ancient: study". CBC News. 17 September 2010. Retrieved 17 September 2010.
- "Neutralization-resistant" refers to strains which are not able to be neutralized by the native immune response due to compensating mutation; see HIV-1 related information.
- . Lay summary available from Bloomberg at "J&J AIDS Vaccine Protects Monkeys in Study as Testing in Humans Begins", published 4 Jan 2012.
- Hansen, Scott G. et al. (2013). "Immune clearance of highly pathogenic SIV infection". Nature 502 (7469): 100–104. doi:10.1038/nature12519.
- Paul M. Sharp; George M. Shaw; Beatrice H. Hahn (April 2005). "Simian Immunodeficiency Virus Infection of Chimpanzees". Journal of Virology 79. p. 3891-3902.
|Wikimedia Commons has media related to Simian immunodeficiency virus (SIV) protease.|
- 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