In late September of 2005, the world was struck with a terrible, virulent plague. In the early days of this plague, it was believed to be well under control. Casualties were few and far between, constrained to indoor quarantine zones, protecting the outside world from the violent malady. These quarantine zones did not last long. Common vermin and pets acted as carriers, delivering this plague out to the greater world.
Men, women and children were all infected. The young died instantly. The old were forced to weather a tortured, wasting existence prior to their death. Innocent bystanders acted as unknowing carriers, delivering the plague from one victim to the next. The death toll rose high enough that major city centers had been almost completely killed off, leaving only piles of corpses to rot in the streets.
We're not talking about the Black Death or a modern pandemic like SARS or H1N1. We're talking about Corrupted Blood, a disastrous plague that struck within the virtual world of Azeroth, hurtling World of Warcraft into the public eye and placing it under scientific scrutiny.