User blog comment:ImperiexSeed/Supernatural Mysteries/@comment-3481504-20120408022053/@comment-1509826-20120408180402

Its not a natural illness, its a supernatural one, but even then its sick an illness, and thus shares traits with one, ie its contagous. For the record there are actually some dieses that can do that sort of thing, particually ones that affect the brain, although this is only a secondary trait, there are none that only do that.

It is like a disease, but it isn't a natural one. And who's to say Pestilence couldn't do that? Just because he didn't use it, doesn't make it immpossible, after all the only time he could have used it to any advantage is when fighting sam and dean, and why infect them with a slow disease that makes them mad, when he had all the much more painful and horrible real diseases to hit them with?