The biology and epidemiology of HIV infections.

The world now has a pandemic of infection by the human immunodeficiency virus type I (HIV-1). More recently, a focus of epidemic HIV-2 infection in West Africa has been noted and this too is spreading internationally. HIV-2 closely resembles a simian lentivirus, SIV; SIV isolates have now been made from African (but not Asian) old world monkeys and SIV infection in macaques may provide the best animal model for HIV. All of these viruses share a tropism for the CD4 molecule, which is intimately involved in their pathogenesis. The immune response to these viruses has yet to demonstrate any protective immunity.