HIV infection in humans came from a type of chimpanzee in Central Africa. Studies show that HIV may have jumped from chimpanzees to humans as far back as the late 1800s. The chimpanzee version of the virus is called simian immunodeficiency virus. It was probably passed to humans when humans hunted these chimpanzees for meat and came in contact with their infected blood. Over decades, HIV slowly spread across Africa and later into other parts of the world. The virus has existed in the United States since at least the mid to late 1970s. To learn more about the history of HIV in the United States and CDC’s response to the epidemic, see CDC’s HIV and AIDS Timeline.