They didn't. Until I opened this thread. Somehow the virus leapt from Enworld to my Google drive where I store information on my game world, and an innkeeper in a remote northern village served it to a traveler, and before I could get my players to kill the traveler he somehow connected with a troupe of Dwarvish thespians on their way to one of my major cities.
As I write this I'm tracking the spread of....oh, god, how did it get to the other continent? My players don't even know that continent exists yet! They don't even have cheese on that continent.
I might have to burn the whole world and start over.