I am a long-time survivor living with HIV for 20 years. I am frequently asked questions concerning the different strains of HIV. I'm wondering how many strains have been identified and, as time goes on, are more strains being discovered? Also does every new strain come from a mutation of HIV? Thanks for your help. You are a great source for HIV/AIDS information.

Hard question to answer because it depends on how specific you want to get. There are type strains (subtypes or clades) that go from A to J. These are somewhat geographical in origin. There are circulating recombinant forms (CRFs) which are viruses that have pieces of different subtypes. Many have been discovered and more continue to be found. These are probably as a result of new infection in someone who was already infected. Finally each patient has multiple viral strains within them. These are called quasispecies, in that they are all not a true unique strain or species, but differ by a small amount from each other.