Wild gorillas carriers of an SIV virus close to the AIDS virus

This new simian immunodeficiency virus, called SIVgor, has the special feature of being genetically close to an HIV-1 variant called group O. Although rarely found in humans, this variant has nevertheless been the source of cases of AIDS.

The discovery of this new virus prompts the research group to ask the crucial question on the source and route for infection of the gorillas. It broadens substantially the scope of research on the ability of these viruses to cross over from one species to another.

In 2005, 40.3 million people in the world, including 25.8 million in Sub-Saharan Africa, were living with HIV. The question of the origin of HIV-1, responsible for the AIDS pandemic, has been stimulating the scientific community for many years.

Some months ago, the team of Martine Peeters, director of research at IRD, and Eric Delaporte, director of the mixed research unit UMR 145 jointly involving the IRD and the University of Montpellier 1, showed the chimpanzee subspecies living in the Congo Basin (2) to be the reservoir of HIV-1 virus group M, the source of the world pandemic and that of another, very rare variant, HIV-1 group N. However, the reservoir of the third HIV-1 group, group O which infects humans (3), remained unidentified up to now.

This team announces, in an article in the journal Nature, the discovery of a simian immunodeficiency virus (SIV) infection in wild gorillas. Samples of faeces collected from different communities of gorillas found in the remotest areas of the Cameroon tropical forest were found to contain antibodies against this virus, called SIVgor.

The genetic characteristics of the virus were present again in three gorillas living more than 400 km apart. Phylogenetic analysis of SIVgor showed it to be related to HIV-1 group O found in humans, essentially in Cameroon and in neighbouring countries.

This discovery of an HIV-1 related virus in wild gorillas does not, however, call into question the fact that chimpanzees are the primary reservoir of SIV/HIV viruses that crop up again in gorillas and in humans. As Martine Peeters of the IRD says, “the viruses of groups M and N are, very clearly, the consequence of inter-species transmission from chimpanzee to humans, whereas the origin of HIV-1 group O is less apparent. It cannot be excluded that chimpanzees infected by HIV-1 group O might have contaminated humans and the gorilla independently, or that the gorilla, having been contaminated by the chimpanzee, might have contaminated humans”.

This work thus opens up a Pandora’s box on the questions and speculations concerning the ability of these viruses to cross over from one species to another.

The main challenges facing these teams for future work will be determination of the prevalence, the geographical distribution and biology of SIV infections in these great apes, not forgetting the question of how the gorillas were contaminated. This last point remains a mystery,all the more so that gorillas are herbivores and that contacts between chimpanzees and gorillas are considered as rare.

Footnotes:

(1) UMR 145: Fran Van Heuverswijn, Cecile Neel, Florian Liegeois, Christelle Butel, Eric Delaporte and Martine Peeters jointly involving the IRD and the University of Montpellier1
University of Alabama (Beatrice Hahn and her colleagues),
University of Nottingham (Paul Sharp and his colleagues)
PRESICA Project of Cameroon headed by Eitel Mpoudi-Ngole.
(2) Keele BF, Van Heuverswyn F, Li Y, Bailes E, Takehisa J, Santiago ML, Bibollet-Ruche F, Chen Y, Wain LV, Liegeois F, Loul S, Mpoudi Ngole E, Bienvenue Y, Delaporte E, Brookfield JF, Sharp PM, Shaw GM, Peeters M, Hahn BH. Chimpanzee Reservoirs of Pandemic and Nonpandemic HIV-1. Science. 2006 , 313 : 523-6

(3) Scientists have known for a long time that the Aids virus shows a very strong genetic variability. Two main types of the virus exist: HIV 1 and HIV 2. HIV 1, the most widely spread in the world, embraces three groups (M, N,O) which manifest different genetic characteristics. Within group M, the most frequent, still 9 further subtypes can be distinguished (A, B, C, D, F, G, H, J, K), genetically close yet distinct.