Simian immunodeficiency virus

Simian immunodeficiency viruses (SIV) are retroviruses that are found in over 40 African primates.

Viruses 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 are widely believed 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 is used to infect an Asian Rhesus Macaque, the animal will develop simian AIDS.

A recent study of SIVcpz in wild living chimpanzees suggests that infected chimpanzees experience an AIDS-like illness similar to HIV-1 infected humans.

History

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 SIV_sm strain found in sooty mangabeys whereas HIV-1, the predominant virus found in humans, is derived from SIV strains infecting chimpanzees (SIV_cpz).

Transfer to Humans

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 TRIM5α in humans and monkeys. This intracellular protein recognizes the capsid of various retroviruses and blocks their reproduction. Other proteins such as APOBEC3G/3F may be important in restricting cross-species transmission.

Unusual case

French doctors treating the 62-year-old Cameroonian woman who was living in Paris said they initially spotted some discrepancies in routine viral load tests.

Further analysis of the HIV strain she was infected with showed it was more closely related to SIV from gorillas than HIV from humans.

She is the only person known to be infected with the new strain, but the researchers expect to find other cases.

Before moving to Paris, she had lived in a semi-urban area of Cameroon and had no contact with gorillas or bush meat, suggesting she caught the virus from someone else who was carrying the gorilla strain.

Analysis of the virus in the laboratory has confirmed that it can replicate in human cells.

Co-author Dr David Robertson, from the University of Manchester, said it was the first definitive transfer of HIV seen from a source other than a chimpanzee, and highlighted the need to monitor for the emergence of new strains.

"This demonstrates that HIV evolution is an ongoing process.

"The virus can jump from species to species, from primate to primate, and that includes us; pathogens have been with us for millions of years and routinely switch host species."

The fact the patient had been diagnosed in France showed how human mobility can rapidly transfer a virus from one area of the world to another, he said. ([1])

Research: Past and Current

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

Dr. Beatrice Hahn of the University of Alabama at Birmingham recently lead 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, pass the virus to their infants, and had a higher infant mortality rate than uninfected females.^[1]

The ICTVdB code of SIV is 61.0.6.5.003. ^[2]

See also

• OPV AIDS hypothesis
• eu-FEDS

References

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