I look forward to seeing cow corpses flung over the battlements.
Ehhhh... I'm torn. I see what Siegbert's getting at. It could just be an unnecessary component that would complicate things and possibly be overpowered/annoying.
But if they could make it work, it might be an interesting feature that could be used situationally. Like, maybe it could have a small contamination radius and take a minute or two to infect (the closer you are, infects faster? It could encourage the use of doctors. and if it got out of hand, guards could block off part of the castle.