HIV-2 is closely related to, but not identical, to HIV-1. HIV-2 is found predominantly in West Africa, where in some areas it is the predominant HIV infection. In other areas it may occur with less frequency than HIV-1. It has also been found in low frequency in Central, East, and Southern Africa. It is spread through sexual intercourse. A few cases have been reported in various Western countries, including the United States, thus far almost entirely in immigrants from West Africa or a few persons who traveled or lived temporarily in that region. Clinically, HIV-2 resembles HIV-1, although in general HIV-2 appears to be somewhat slower to progress to AIDS. Antibodies to HIV-2 cross-react to some extent with standard serologic tests for antibody to HIV-1; the frequency of cross-reaction has been variable (8%-91%). Also, cross-reactivity to HIV-1 tests decreases as severity of HIV-2 infection increases. The typical HIV-2 reaction pattern with HIV-1 tests is a reactive HIV-1 screening test result plus an “indeterminant” Western blot result.

Specific ELISA tests for HIV-2 antibody are not available, and a Western blot technique can be used to verify HIV-2 infection. In addition, commercial tests are now available designed specifically to detect both HIV-1 and HIV-2. These tests are being used predominantly in blood banks.