The author writes about the history of knowledge being attained when it comes to infections diseases - there's plenty of interesting stuff in there but the prose itself was not as attention-holding as I'd have liked. That said, I did learn a lot of things about infections - from the fact that the "Hollywood" version of Ebola is far worse than the real disease (people don't 'bleed out through all their pores') but that there is a virus that infects tent catapillars in exactly that manner (causing them to essentially melt) that itself might be responsible for the huge swings in that catapillar's population over the years - and by extension this might pertain to many other fauna.
Another point of interest: the way some animals (like certain bats) can be reservoirs of pathogens, making it nigh impossible to eradicate the disease without killing the entire reservoir species (assuming that it's even known). And HIV seems to have crossed over from monkeys in Africa around 1908 - but didn't spread much for decades.
The upshot of the book is that humanity - ourselves a kind of infection on the planet - is due for another pandemic, though nobody can guess as to from whence that will come. So lots of good factoids, but a bit too flowery in the writing.