I recently read "Marvel Zombies vs. Army of Darkness", and it reveals that the Zombie Plague seen on Earth-2149 started when
an infected Sentry was teleported to 2149 along with Ash.
How was this character infected, though? If he's Patient Zero, then where did the plague come from originally? Where did it start?
I've read almost all of the Zombie-related story arcs (still missing a couple) and have yet to see this question answered.