Flu, for example, comes from ducks and pigs. Often the virus does not make its natural host, or reservoir, sick. It must undergo genetic changes to infect another species such as humans, changes that can cause illness. Hahn's team found evidence of such genetic changes in their chimp SIV, known specifically as SIVcpz. That is just where this subspecies of chimp lives.
Many scientists think the virus spread to people through infected ape or monkey meat.
People in some parts of Africa often hunt and kill chimpanzees, and a virus can easily spread from blood during butchering. There is a second strain of HIV that infects people, known as HIV-2. It is believed to have started out in a monkey known as a sooty mangabey. Why, in the Belgian Congo in 1957-8. Thank you and a bump.