If you want the book to remain mysterious, steer clear of all reviews. Including this one. 
 Cordyceps is freaking creepy, and has found its way into many modern zombie stories, like the game The Last Of Us. There's nothing more gross to me than mushrooms that take over people. I saw a documentary about how it takes over ants, and was terrified of it ever since. On real life it can't hurt humans, but still... 
 It was an excellent book, with great motifs and disgusting visceral imagery. The girl is a lovely character, but all in all the characters didn't leave much of an impression on me. Except the "good" doctor Caldwell, who is a total sadistic sociopathic bitch. I hated her guts, and for that I loved her for making me feel. Even so she could have been more horrible. 
 The authors vocabulary gave me pause dozens of times. He frequently used archaic terms, strange meanings of terms, and words I'd never even heard of. It was frustrating sometimes, and I would have been in deep trouble had I not read this on my kindle fire with my trusty highlights and dictionary. This was especially strange given the rather casual way the book was written. To be fair, it was if different characters had different voices in their chapters, so twas intentional I presume. 
 Verdict: Great book. Read it.