Human immunodeficiency virus

Two species of HIV can infect humans: HIV-1 and HIV-2. HIV-1 probably originated in southern Cameroon after jumping from wild chimpanzees (Pan troglodytes troglodytes) to humans during the 20th century. HIV-2 most probably originated from the Sooty Mangabey (Cercocebus atys), an Old World monkey of GuineaBissau, Gabon, and Cameroon. HIV-1 is the most virulent, is the easiest transmitted, and is the cause of the majority of HIV infections globally. The earliest known instance of HIV-1 infection in humans is a plasma sample taken in 1959 from an adult male living in what is now the Democratic Republic of Congo. HIV-2 is less transmittable and is largely confined to West Africa. Although a variety of theories exist elucidating the transfer of HIV to humans, no single hypothesis is accepted and the topic remains controversial.