This might be a lost cause trying to fight the creator on this but like wooly said, these zombies kill by tearing humans apart limb from limb using teeth fingers anything, and the victim isn't exactly gonna sit there and take it are they? They'll fight back. The result would be one giant bloody mess but the victim is killed before he gets a chance to turn (2-3 minutes?) anyway there's a giant bloody mess of a corpse, we know zombies drool and salivate like mad when they have the scent of a human so there SHOULD be a transfer of fluids/blood between victim and zombie, and this SHOULD be the case for almost every body in that pile. So all together a good bit of zombie toxin should have been in and around those bodies, I'll guarantee u
angel n
Riley got goo in heir mouths and eyes, so the way I see it, had the virus been active outside the host body, Rigel (Riley/angel) shoulda turned.
But that could totally not be the case in which case PLOT HOLE! TAN TAN TAAAAAAAN!