I found a very good article on the subject.
http://discovermagazine.com/2008/nov/27 ... mic-emerge
It's been *toned* down so that the average non-biologist can understand the concepts better.
I didn't read the article (I just skimmed it thru and thru) because I'm already well versed in the area of infectious disease. However, I would add - if it's not pointed out in the story - that I don't think we've yet to see the worst of the worst, as it were. There are still many species that we haven't encountered as of yet. Species that, for instance, live in the deepest regions of the Congo or the Amazon. The more we "slash and burn" our way (in the quest for more timber or farm land) into those respective regions the more likely we'll come in contact with either new species (those not yet known to science), or rarely encountered species that harbor viruses or bacteria that have the potential to be highly lethal to humans.
It is inevitable that sooner or later we will be hit with a new TB or "Black Death" that's going to wipe a 1/3 or more of our total global population.