Sorry to bring up Doctor Who again, but in the episode New Earth (If you don't understand what's going on read this: http://tardis.wikia.com/wiki/New_Earth_%28TV_story%29
) they had people infected with every disease in the universe. Now, let's have every disease GIANTmicrobes has infect someone as an experiment. Then, as part of the experiment, they release nanobots to kill all viruses and bacteria (and prions and parasites etc...) in the body. But they go psycho and kill every cell in the body. The lab that the body was in (Let's call him "Bob") goes under quarantine, and the scientists are forced to leave. It's up to the Microbes to destroy this nano-threat!
We're missing Aerials, Aquatics, Critters, and some Menageries, but we have most of them!
Everyone gets to make up a nanobot if they want, each with its own abilities. We start with Standard-Bot, but we make up some more as we go along. Each player picks one Corporeal or Disease to play as. Name, gender, personality, etc. This doesn't have to be scientifically accurate! Brain cells can swim in the blood stream if they want for the purpose of this game only! We work together, so no T4s killing E. Colis!