Yeah everyone has the disease regardless of how they die, in the comics the reveal came at the prison when Tyrese's daughter dies from getting shot and she turns, I forget who they did it with on the show...Shane?

 

Though I'm not sure how the biting seems to work, it seems if you already have the virus then getting bit shouldn't do much (i can understand if they ripped off a chunk of your arm and it gets infected, but just getting bit seems lame.  Probably over thinking it though. 

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