I'm assuming that you are the GM? If so, make an adventure of it: there is a local herb that will slow/heal the afflictions, but they will need a lot of it. When the character go to harvest it, turns out it's already been harvested! Find out who did it, see how much of the herb you can recover... if you don't have enough, who do you choose to heal?
Yeah, I'm going to second this suggestion. As the GM, you can give them a way to cure disease whether they have the mechanical means at their disposal or not. In fact, given that this is an entire village and not just a few characters, you almost have to provide means of providing mass cure; a ritual isn't going to cut it.
In other words, I wouldn't worry too much about finding something in the books to cover this.
Just out of curiosity, how did these people contract said diseases in the first place?