The AIDS pandemic is expanding continually and effective means for protection and therapy to halt this development have still to be established. Human immunodeficiency virus type 1 (HIV-1) accounts for most of the AIDS cases and has been subject of extensive research for >20 years. HIV type 2 (HIV-2) has received much less attention as a cause of AIDS, but should be considered carefully for two major reasons:

The actual number of HIV-2 infections may be underestimated, as a result of poor monitoring and miss-diagnosis, in part due to unawareness in areas where HIV-1 is more prevalent. Although HIV-2 was first detected in endemic West African populations, it is not restricted to this area. Today HIV-2 infections have been identified in many parts of the world, including countries that have no direct links with Western Africa. Accurate discrimination between HIV-1 and HIV-2 is important because the efficacy of certain HIV-1 antivirals may be limited for treatment of HIV-2. The pathogenesis and transmission rates of HIV-2 are generally more moderate than those of HIV-1, which makes this virus a valuable tool for studying these processes. The differences and similarities between these human lentiviruses (and other primate lentiviruses) allow for identification of factors (determined by host genetics, immune responses or the virus) that contribute to viral virulence. Knowledge of these factors and their role in the course of virus infection may facilitate disease management and vaccinations strategies.

This review discusses what is presently known about HIV-2, with respect to epidemiology and virus spreading, the course of infection, efficacy of antiviral treatment and virus characteristics of HIV-2 variants and how they compare and differ with HIV-1.