World War Z by Mel Brooks: abridgment vs. unabridged version?

I have to write a paper on World War Z by Mel Brooks due next week. I haven't read it yet, but I do have the audio-book which is abridged (there is no other version that I am aware of). I was wondering if anyone knew both versions. My plan is to listen to the book to get an idea of where certain stories are so I can reference them as I write my paper, but if I am missing half the story, it won't be all that helpful. Does anyone know what is left out and if it is at all significant?