What if superman ever contracted a disease?
Okay, now this isn't a question focused on whether it's possible, but are there diseases that could affect him? Suppose some creature survived from the krypton explosion and came to earth carrying diseases from krypton that could affect him. Or what if some scientist developed a virus to kill him (or the virus merely evolved on its own.) Not only would this affect superman, but the alien disease could affect humans as well. That would be interesting I think. The villain, or creature, or whatsit could threaten the world and incapacitate it's greatest hero, which would make a very challenging villain indeed. The disease wouldn't completely incapacitate him though, It'd still be interesting to see him fight when he's been weakened. I think this would be a very interesting comic, has this been done before?