No one knows exactly how it happened. It may have entered through a cut or bite wound, the blood of a chimpanzee seeping into an exposed fingertip or forearm or foot. But in the early 1900s, probably near a West African rainforest, it's thought that a hunter or vendor of bush meat -- wild game that can include primates -- acquired the first strain of a simian immunodeficiency virus that virologists consider the ancestor of HIV. A new study led by the University of Nebraska-Lincoln has supported this hypothesis by reporting the first in vivo evidence that strains of chimpanzee-carried SIVs can infect human cells. They include the SIV ancestor of HIV-1 M -- the strain responsible for the global HIV pandemic -- and another ancestral strain of HIV found only among residents of Cameroon. Yet the researchers further discovered that the SIV ancestors of two HIV strains not identified in humans also managed to invade human cells after multiple exposures in the lab. https://www.sciencedaily.com/releases/2016/07/160722092947.htm
