From what I understand, there will have to be a collaborative effort on the part of more than one class to complete the quest for a cure to the plague. The alchemist covers one part of it... after getting the plagued hearts (which I believe they have to have help getting), and making a potion of some sort (I think I read this potion is good for curing for a period of time longer than that of Cure Noxious but still not permanent), the alchemist returns to the NPC and is told that they still need to determine the origin/cause of the plague which must be done by some other class.
Sooooo... the quest will not be completable by any one class, rather a collaborative effort by more than one. Sounds like a good quest for members of a guild to take on.