... He is. You find him experimenting on a woman he intentionally infected with the plague.
Though I'll also note that Dunwall is a pretty crapsack place. As far as the nobility is concerned the plague is the commoner's problem, and they do not even pretend to care about the plight of the common people (another example of which is coming up soon). Even you - playing the ostensible hero of the story - are not trying to find a cure or clean up the city's rat problem; you're trying to put Emily on the throne.
Oh, you have no idea. It gets SO MUCH worse.
Something I've noticed about vidya is that few games that are the first to a trend really get credit for it. It's usually the second or third game to try that hits it big (which makes sense, they can see the errors the previous one made and build on its successes).