What if TWD "zombie virus" and taking into consideration it's never once disclosed in the show (TWD) but is infact related to the "zombies" Will mentions closer to the end of Season 1 of Sanctuary...as to say they are in the same universe and The Sanctuary is infact the cause of the show "The Walking Dead" since Sanctuary ended in 2011 and TWD began in 2010....who's to say with all the chaos from last seasons of Sanctuary that is not what happened...i mean you gotta admit Daryl said when asked what he did PRE-Z "You Wouldn't Believe Me If I Told You"...
Maybe he worked for the sanctuary....LOL idk crazy fan theory tell me what ya'll think