Here's my take: we already know wolves, coyotes, bears, leopards, lions and tigers, along with everyother land carnivore will gladly add a human to the dinner menu of the chance poses itself. In the event of an apocaliptyc event, those would be already accounted for as dangers.

Dogs, I'd risk even domestic pigs, once cut off from human care, would become predatorial. Dogs, even today, can spontaneously form wild packs, capable of predatorial behaviour and aggressive towards humans. Pigs, on the other hand, have a scary capacity to regress and become feral when let loose on the wild; there are records of domestic pigs escaping from farms only to be taken down months or years later by hunters, turned into gigantic animals, covered in thick air and boasting long and sharp, tusk-like, teeth and a very mean and aggressive temper, not like the common wild boar that will actively avoid humans if possible.

These new predator would pose more of a threat than those we already account as such.