From the White Wolf Wiki, the most complete White Wolf reference

The Great Contagion is a plague which struck Creation at the end of the First Age of Man; the plague was so virulent that it killed 90% of the infected population. The Contagion was engineered by the Deathlords, particularly the Dowager of the Irreverent Vulgate in Unrent Veils.

• In Exalted: The Autochthonians, one of the invasion scenarios is based around the idea that Creation's populace has developed immunity to the Great Contagion, and that Autochthonia is devastated by it on contact.

• The cover of the Book of Bone and Ebony shows the creation of the plague at the Well of Udr.