The Hot Zone
Holly shit, this book is horribly great, and it's nonfiction which makes it more scary but fascinating. The book is about the true story of the Ebola virus. All the events described are true. You can even check it on internet. The story is so dramatic and so well described that you can understand, imagine and also have the feeling of how this lethal virus works inside a host, and how it would feels if you break with Ebola.
This book got me hooked. The virus is so frightening and lethal, and there is not any vaccine or drug 100% effective for it yet, just 1 experimental vaccine. There are 5 different Ebola viruses, and noone knows where they hide. The fatality rate is from 25% to 90%.
There are many deadly viruses and I have learned that we had one very dangerous here, called Junin virus which is a hemorrhagic fever. No cases have been reported since 2008 though.
If you think about those viruses and how they work in the human body and how fast some of them could spray and kill a large number of people, you can think that the human race is threatened.... or you can think that the earth is threatened by a virus called "humans" and it's only trying to get ride of that lethal virus.