The Hot Zone: A Terrifying True Story by Richard Preston
Ya.. this book will keep you up at night. It's pretty gruesome, and horrifying, and eerie and mysterious. Ebola is scary as hell and this book talks about its origins and attempts to find where it came from. The author takes a lot of creative liberty in retelling the stories in the book that span a few decades, but I believe it's also well researched and includes plenty of interviews with people on the ground in Africa, at the CDC and the US Army who are leading experts on it. Really unpleasant and sobering to read about how delicate we are to this little bastard worm of a virus.