Very little is known about infection rates in humans before the 1970s, although some isolated cases of HIV infection have been detected in individuals that died in the 1950s and 1960s. A study that used complicated computational models of HIV evolution indicated that it was probably even earlier, in the 1930s, when the first human infections arose although this is far from certain. What we know is that HIV is similar to, and most probably descended from, another retrovirus that infects non-human primates. This retrovirus is called the simian immunodeficiency virus (SIV) and has been isolated from chimpanzees in West Africa. However, whether SIV crossed species in Africa or elsewhere (or indeed in several places and at different times) is unknown and would be difficult to prove.
Whatever its origin, our knowledge of how HIV infects and replicates in cells has steadily grown within the last 20 years and has allowed the enormous advances we have made to confront the AIDS pandemic. Dr Peter Piot, executive director of UNAIDS, optimistically summarized the outcome of this effort in the closure ceremony of this month’s XV International AIDS Conference in Bangkok:
"I truly believe that, for the first time, there is a real chance that we will get ahead of the epidemic. And this momentum has its roots in both the science and the activism of the last decades. But our challenge remains on how to raise action on both fronts to the level we need to achieve full success."