system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] Who carried the earliest origin of the zombie virus of Earth-2149?
gpt
A version of the Sentry who was sent to Earth 2149 from Earth 91126, and then bit that universe's Captain/Colonel America, Hawkeye, and Ms. Marvel shortly thereafter.

It's unknown where the Zombie chain in Earth 91126 started, but it's basically stated that that some weird ass causality loop was implemented by a Watcher to keep the virus contained between the 2 universes: Earth 91126 sends an infected Sentry to Earth 91126 which then sends infected heroes into the past of Earth  2149, which starts the infection there, and causes sequence of events to repeat themselves.