I dealt with a plague last year: a small demon, inhabiting a well, or perhaps it was just bad water and rats. It hardly matters. I used fire and salt and the prayer of John the Baptist, also called Johannes Fontus, who watches over springs and freshets. When I was a child, I learned the song of his severed head upon the water, and it is known to drive out the lesser beasts of Angra Mainyu. If one has such a thing, why not use it? At least, I never knew a plague made worse by holy songs. For the sake of argument, I also had them drive out the vermin, drain the whole cistern and burn it dry, then rake out the ash and reline it. Vastly expensive, and there was a lot of grumbling, but do you know: one or the other did the trick. That’s why my prices are high these days. I actually get results.