Certainly this idea of so-called emerging infectious diseases is a big concern in the medical community. There have been, I guess really with the advent of HIV probably in the 80's, this idea that new and uncharacterized infectious agents really were emerging. I think that, in general, that there was this perception that because of medical advances in the last hundred years that infectious diseases were really a thing of the past, that it wasn't very interesting. We had discovered all the viruses and bacteria, we have drugs that can fight them, antibiotics, and now we should concentrate on cancer and heart disease. Well, it turns out that infectious agents and nature are still are a lot cleverer than we thought, and clearly we have not won this battle about infectious agents.
I think that the huge population growth in the world and the expansion of humans into remoter areas of the world and the spread of humans from one place to another has clearly increased the ability of infectious agents to gain a hold in human populations. So things like Ebola virus and Hanta virus that are incredibly nasty viruses that really kill people, but in really isolated places, still exist. But we shouldn't forget things like influenza viruses, which sound very boring and commonplace, still have the potential to cause great medical harm.
So I just don't think we should forget the lessons of microbiology, that infectious agents are constantly trying to figure out ways to infect people and that we really can't consider this battle won.