Talk:Corvo's Mask/@comment-187.37.173.163-20121022012153/@comment-3410662-20140415193754

A plague is not like a poision. There are several differences, but the easiest is that a plague is a living thing and a poison is not. We've also seen that the Outsider doesn't protect one from all venoms, either; Corvo was poisoned, and the Brigmore Witches are vulnerable to sleepy-time darts.

I like the theory that Serkanos was hit with the Rat Plague at some point in its past, and that as a result the inhabitants of that island built up an immunity to it. That would explain why neither Daud nor Corvo need to worry about getting infected, because you can make a run through the game without using the Elixirs or the Remedies.

The High Regent may have brought the Rat Plague to Dunwall, but that doesn't preclude the possibility of the Outsider's meddling, nor does it prevent him from getting involved afterwards. We've seen that he's more than willing to help spread the plague via one of the Tales of Dunwall episodes, for example.