Wererat

A wererat is a fictional creature akin to a werewolf, but shapeshifting into the form of a rat instead of a wolf. This type of lycanthrope is not found in historical legends, but has become common in modern role playing games and fiction inspired by them. They are commonly portrayed as sewer-dwelling scavengers and opportunistic thieves.

See Ratkin for wererats in White Wolf's "World of Darkness" role-playing setting.

Wererats also appear in the Anita Blake: Vampire Hunter series.