On the topic of the 'roadkill-eating werewolf' do note that most mundane diseases (ie: the kind of thing that would be contracted by eating improperly prepared, raw, or rotting food) have abysmally low save DCs, and thus are not likely to cause any SERIOUS problems for an experienced D&D character.
I recommend instead adding roleplay effects such as indigestion, diarhea, and the like, with no hard game mechanics except in the most severe cases (if they go on a roadkill binge-eating spree, then maybe hit them with the Sickened condition until they can receive magical assistance to cure it, or for 2 or 3 days if they decide to just wait it out)