Many viral diseases that affect us originate from viruses crossing over into humans from another animal species and when a virus makes such a jump it may find the human species to be less hospitable for its replication. In this, HIV-1 is no exception: there have been four separate crossover events between primates and humans (M, N, O and P) but only one of these (M) has achieved pandemic proportions. It has been suggested that the success of HIV-1 group M is because the chimpanzee virus that originated group M was probably more primed to both enter and survive in humans than the primate viruses that originated the three other groups.

Scientists determined the gorilla as the animal origin of HIV-1 group O. Credit: “Gorilla 2582”. Licensed under CC BY-SA 2.5 via Wikimedia Commons

To understand the origin of HIV-1’s second most successful group (O), researchers collected thousands of fecal (the more scientific term for poop) samples from gorillas and analyzed them for the presence of gorilla SIV (SIVgor). By looking at the genetic similarities shared by SIVgor and HIV-1 they could determine that HIV-1 group O emerged following the transfer of SIVgor from gorillas to humans.

While this has been the focus of most media reports about the published paper, the researchers both asked and answered a far more interesting question: could the different primate origins of groups M and O explain why only group M dominates the global HIV-1 scene. They address this by comparing the proteins of these two viruses and according to Dr. Athe Tsibris their results show that “the inability of group O to spread extensively in the human population is due to a lack of opportunities rather than a genetic effect”. This demonstrates that chance plays a major part in determining which viruses that jump into humans will become global pathogens and which won’t.

Managing Correspondent: Fernanda Ferreira

Acknowledgements:
Special thanks to Dr. Athe Tsibris, an assistant professor at Harvard Medical School, for expert commentary on the origins of HIV.

Original article:
Origin of the HIV-1 group O epidemic in western lowland gorillas

Other media coverage:
Two Strains of H.I.V. Cut Vastly Different Paths

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