An atlas of mammalian viruses Book

I read this book nearly 7 years ago. The story always hung around in the back of my memory, but I couldn't remember the title until I searched for it online.
Although I did not like the sudden ending that left some little things unexplained, the rest of the story was a great read for me, as it was my first (supernaturally) mystery book. I admired Fanny, thought her stepsister very silly, and positively despised the red-haired man.