The bite is toxic in so far as it's highly septic, on account of being full of rot. It's like the pits in Komodo Dragon teeth that catch bits of food to sit there and decay giving them an infectious bite, only more so since the walker's whole mouth is rotting flesh. It's unclear whether there's a higher level of toxicity apart from that.
Amputation can save people from getting sick and dying, just like with gangrene.
Die by any means, you will rise, even if you've never seen a zombie. The infection is pandemic.
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...You are Number Six. Respect Popeye