Distinguishing HIV-1 and HIV-2
The widely used term, "HIV," generally refers to HIV-1, the most prevalent form worldwide. However, two types have been identified: HIV-1 and HIV-2. Both are transmitted via the same routes,13 both are associated with similar opportunistic infections, and both cause AIDS.14 However, HIV-2 has a lower viral load,14-16 is less pathogenic,15,16 generally progresses more slowly than HIV-1,16,17 and is mostly confined to West Africa.
The breakdown of the immune system from HIV-2 infection is less dramatic and occurs at a slower rate than it does with HIV-1.18 Also, neutralization escape—that is, the ability to mutate and dodge an attack from neutralizing antibodies—is less common in HIV-2 infections.19 Thus, characteristics of HIV-1 including a higher viral load, greater pathogenicity, and the ability to escape neutralization more often, contribute to its widespread prevalence.
Both types of HIV appear to have originated from simian immunodeficiency viruses (SIV) in chimpanzees (Pan troglodytes) and sooty mangabeys (Cercocebus atys; SM).20,21 SIV are retroviruses that infect primates; certain strains of SIV are thought to have mutated into HIV and subsequently infected humans.20,22