> The problem is exponential growth and how hard these things are to kill. Zombie bear, for example, is basically invincible and will probably make a lot of zombie people. 

Bears to begin with aren't exactly all over the place and maybe a considerable problem in Colorado and up in Canada. But human growth would have pushed them deep into thick wild life reservations. So chances are a zombie bear won't "sense" a human as readily as a zombie-person because they're not anywhere where there are people. Zombie tigers: sure. But there's also not many and they're only all of four places set aside for them in India. Push comes to shove high-explosive ordinance will take care of them if the Indian military needs to sacrifice an iconic species just to keep them from killing enough people to make a new hot-spot for an epidemic.