Unusual Apocalyptic Blights and Plagues

[D20ragon]

I'm looking for things more on the mundane side.
Mundane in that I'm just not interested in overtly magical illnesses, (no changing into insects or melting into olive oil) though having the disease be subtly magic is certainly fine. Essentially, I'm designing an end of the world disease scenario for a fantasy game I'm running, and apart from the usual "contagious madness/death" disease, I'm a little stumped. The only thing I can think of at the moment is a plague causing infertility, which could be interesting thematically, but I'm curious to see what ya'll have to say. Essentially the disease should be a little out of the ordinary in terms of its effects and/or the way it applies said effects, while still being able to cause the collapse of a society.