So there's an idea that we may have been inadvertantly evolving super diseases that are extremely resistant to conventional medicines. Essentially, as we know, drugs are never 100% effective. When a drug is used, the bacteria/viruses that survive are ones that are resistant to that particular drug and then can pass on their resistance, thus rendering the drug less effective in the future.
If you Google "drug resistance evolution", there's a bunch of stuff written out there on it.
There's pretty much a race going on with diseases evolving vs how fast the drug manufacturers can keep creating effective drugs - a pretty nasty problem to crack.