Game: Cell: emergence

We like to think that if any nasty germs gain access to our insides, our helpful antibodies will simply kill them all off and we won't even notice. Perhaps we'll get a bit of a sniffle, but that's it. Of course, then you get all the various movies and books and the like that envision the story of a virus that our bodies simply cannot cope with, and it ends up going on a rampage through the human race, cutting the world population down to size.