Spillover: Animal Infections and the Next Human Pandemic

by David Quammen

That was the case in 1999, when Feng Gao produced a phylogenetic study of SIVcpz and its relationship to HIV-1. At the time there were only three known strains of SIVcpz, all drawn from captive chimps, with Gao’s paper adding a fourth. The work appeared in Nature, highlighted by a commentary calling it “the most persuasive evidence yet that HIV-1 came to humans from the chimpanzee, Pan troglodytes.” In fact, Gao and his colleagues did more than trace HIV-1 to the chimp; their analysis of viral strains linked it to individuals of a particular subspecies known as the central chimpanzee (Pan troglodytes troglodytes), whose SIV had spilled over to become HIV-1 group M. That chimpanzee lives only in western Central Africa, north of the Congo River and west of the Oubangui. So the Gao study effectively identified both the reservoir and also the geographical area from which AIDS must have arisen. It was a huge discovery, as reflected in the headline of Nature’s commentary: FROM PAN TO PANDEMIC. Feng Gao at the time was a postdoc in Hahn’s lab.