KickballDeac
Bernie Eskimo Bro
Because decomposing bodies tend to be riddled with bacteria and that leads to infection which kills you.
But infection with the zombie 'virus', not run of the mill bacteria. Andrea got bit by a fresh walker and was 'burning up' when they found her.
(I'm just being a fanboy and nitpicking, I don't actually care about the bio/immuno-logistics of the show that much)