Human immunodeficiency virus type 2 (HIV2).

In the mid 1980's a second human retrovirus, capable of causing the acquired immunodeficiency syndrome (AIDS), was isolated from patients of West African origin. This virus, now called human immunodeficiency virus type 2 (HIV2), was found to be distinct from human immunodeficiency virus type 1 (HIV1) but closely related to simian immunodeficiency viruses (SIV). Although the genomes of HIV1 and HIV2 are similar there are significant differences in nucleotide and amino acid sequences, most marked with the envelope genes and proteins. Both viruses, however, bind to the same CD4 cellular receptor. HIV2 is largely confined to West Africa where it is the dominant HIV, though patients infected with HIV2 have been described in Europe and America. Its transmission, clinical features and immunological effects are similar to those associated with HIV1 infection. However, there is some suggestion that the incubation period from infection to clinical disease may be longer than with HIV1 and that HIV2 may be less pathogenic. Patients with sera that react with both HIV1 and HIV2 antigens have been described, but it is unclear whether this represents serological cross reactivity or true double virus infection. Testing for HIV2 antibodies may become increasingly necessary in HIV2 non-endemic areas.