I read a short novel some years ago, based on pretty much the same premise, except, rather than there being numbers of infected zombies, there was just this one malevolent being, who could take over bodies after they died. The twist was that he could keep the bodies he inhabited moving and human-like for a limited period of time. They started gradually to decay. In the climactic scene, the protagonist had managed to corner him in an old house and blow up and burn the house. As the cells started to try to creep back together and reassemble themselves on the walls as a humanoid, the hero came in and blasted them with a flame-thrower...