The phrase “emerging disease”, to describe an infectious disease that is new to humans or which is suddenly increasing its geographical range or number of cases, dates back to the 1960s. But it was the realisation in the late 1970s and early 1980s that the world was in the throes of previously unrecognised pandemics of genital herpes and AIDS, that really propelled the term into the mainstream. The causative agent of genital herpes was type 2 herpes simplex virus (HSV-2), a pathogen that was reasonably well-known at the time, but whose capacity for explosive spread had been underestimated. AIDS, on the other hand, was a completely new infectious agent – one which we now know had been spreading unrecognised since the early 20th century.

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