There's Nothing New Under The Sun

They were the "witches" often spoken of in folklore. The "vampires" that fed on the blood of the living hiding in the shadows afraid of the power of conviction, faith not simply in the cross of Christianity. Those scary beasts and trolls that dragged unwary children underground never to be seen again until their tiny, lifeless bodies showed up as if specifically placed to be found readily. Tiny bodies tortured and flayed. Drained of blood. The townspeople calling for the expulsion of this group of vipers time and again. They poisoned the wells and created plagues throughout history. The victim populations always had to take the poison into their bodies voluntarily in order to infect the population. Then plague broke out.