Medical science has come a long way since the days of blood letting and leper colonies. We can now cure all kinds of diseases that mowed people down in their droves back in the Olden Days. But, however far we've come, there are still diseases out there that have remained one step ahead of us all this time. Some of these diseases are so rare that we've not been able to study them long enough to even find out what causes them. Others, however, are incredibly common and yet we still can't seem to figure out how to defeat them. Both rare and common diseases alike continue to puzzle and perplex scientists. Some diseases require us to delve deep into our own DNA, some are the work of tenacious and dangerous viruses that will do anything to avoid extermination and some of them we simply don't know the cause of, let alone the cure.