Acquired immunodeficiency syndrome (AIDS) received its utilitarian name in 1982, a year after U.S. doctors recognized an epidemic of pneumonias, rare cancers and assorted bacterial infections among mostly male, mostly young and mostly previously healthy adults. The next year French researchers isolated the cause of the immune system collapse that defined the syndrome: a virus that selectively infects and destroys immune cells themselves.
The human immunodeficiency virus (HIV), which today resides in more than 30 million people and seemed to come out of the blue in the early 1980s, is now known to have been infecting humans for at least a century. Recent studies of preserved tissue samples show HIV present in the former Belgian Congo in 1959, in Haiti by 1966 and possibly in the U.S. as early as 1969. The historic specimens also let scientists calibrate “molecular clocks” to trace the evolution of the virus back to its first appearance in humans.