Wondrous item, common (requires attunement)
This hazel walking stick attunes the moment it is touched. While holding it, you are immune to disease.
Curse. This stick is cursed. Attuning to it curses you until you are targeted by a remove curse spell or similar magic. Rats congregate from all around you wherever you go. In common urban areas, this results in a swarm of rats every 200 yards; in rural fields, a swarm of rats every mile; in lush wilderness, a swarm of rats every 10 miles. Shorter distances and desert lands may produce a number of single rats.
Inspired by a short Brothers Grimm tale: The Ratcatcher, brought to my attention by the most recent Astonishing Legends episode. Definitely primarily a trick to be played on the players, but a pretty harmless one that might have some legs.