The Origin, Evolution, and Epidemiology of HIV-1 and HIV-2

HIV-1 originated in the early 1920s in southern Cameroon and the Democratic Republic of Congo. From Africa, HIV rapidly spread in the late 1960s to the Caribbean and then the United States, Europe, and other areas of the world, leading to the global AIDS pandemic. Both HIV-1 and HIV-2 descended genetically from Simian immunodeficiency virus via cross-species transmission. HIV-1 group M was the first lineage discovered and represents the pandemic form of the virus. Group M consists of nine viral subtypes (A–K), has a widespread distribution, and accounts for approximately 95% of all HIV-1 infections. HIV-2 was not discovered until 1986 and makes up approximately 3% of cases worldwide. It is found mainly in West Africa. The genetic diversity of HIV does not appear to significantly affect viral response to antiretroviral therapy. However, viral diversity continues to present challenges for the development of an effective HIV vaccine.