Yeah, I heard about most of the little kerfuffle over rats with treasure. While not part of the original discussion, it was interesting watching the ripples pass from g+ to the blogosphere. But this got me thinking. OK, why would rats have copper pieces? Then I came up with this little idea.
Armor Class: 7 
Hit Dice: 1d4 hit points
Attacks: Bite (1d4)
Saving Throw: 17
Special: Carry Disease
Miser rats are the product of a young wizard’s failed attempt to end a vermin infestation. The wizard conjured a magical plague to wipe out the rats. Unfortunately, the surviving rats adapted to the disease and continued to thrive. Miser rats are affected by and carriers of a blood thinning disease (know as Artemis’s Rat Anemia). Because of this they have a craving for some metals. Primarily, copper and iron. Their nests are often littered with gnawed nails, needles and coins.
A character bitten by a Miser Rat must make a saving throw versus disease. If the character fails then he has contracted Artemis’s Rat Anemia. Until the character is cured of the disease, he has a -2 penalty to Strength and Constitution. Natural healing occurs at half the normal rate and magical healing is one half effective.