Plagued Vermin are rats that have been affected by eating plagued grain from the Conspicuous Crates found in towns and the plagued corpses littering the streets. They are part of the Zombie infestation world event.
Attacking one causes the attacker to become infected.
Unlike Plagued Roaches, the Plagued Vermins aggro city guards. These will become infected, and will turn into zombies if not cleansed fast enough.
Killing them with a pet will prevent them from spreading the plague.