Bio weapons have been used since the days of castles and sieges, where the attacking army would launch dead/sick animals (typically cattle) over the enemies walls in attempt to make defenders ill
It is a good thing we have good hygiene, antibiotics, and specific vaccines against the plague in modern times
(some countries still have a stockpile of antibiotics against this disease just in case of a bio terrorism attack)
It's getting more and more depressing that my very modern country sucks at handling a quarantine worse than George Washington with Yellow Fever in the 1700's.
Oh, well good thing the fucking national capital has 0 magic users guarding their walls incase this exact thing happens. Especially when they're on high alert for a group with magic users they think will try to bum rush the gates and already knew which gates they'd use. Fucking idiots.