HIV Variation
Like any virus, HIV has mutated to form distinct subtypes. Today, there are five major subtypes — A, B, C, D, and E — each of which tends to predominate in specific areas of the world. All of the HIV subtypes most likely originated in sub-Saharan Africa. People infected with a single subtype then carried it to specific regions in other parts of the world. Over time, each subtype became established in different geographical areas. The virus then underwent further mutation to create individual strains of each subtype.
One would assume that this mutation process would continue indefinitely. But this has not been the case. In fact, only a small number of mutations give the virus an advantage and are therefore retained in the HIV genome. HIV has to retain certain characteristics if it is to remain effective. That’s why we believe there are a limited number of subtypes and strains. Although new minor subtypes have been identified, no new major ones have been discovered in more than 15 years. Click here for more information about genetic variation in HIV.