Plague that made the Ancients leave the Milky Way

I, for one, do not believe that the Ori sent the plague to the Milky Way that made the Ancients leave. Remember that the Ori didn't know about the Milky Way until Daniel & Vala's slip up. So, I believe that the Ancients most likely experimented with some sort of bacterium or virus or the sort and nearly killed themselves, I mean it wouldn't be the first time.