I remember reading about a village that actually brought in large numbers of cats to deal with their rat problem, believing that the rats were spreading the pla

I remember reading about a village that actually brought in large numbers of cats to deal with their rat problem, believing that the rats were spreading the plague. The cats did a fairly successful job of killing the rats off and, as a result, they had a huge plague outbreak. The scholars at the time concluded that the rats and the plague were unrelated. With the benefit of hindsight, we know that the plague is spread by Yersinia Pestis, which is carried by rats and transmitted to humans through fleas. The fleas generally prefer the taste of rat blood and only bite humans when they get really hungry. Of course, when a bunch of cats kill the rats, they have to make do with what's available and the fleas start going after people, vomiting the bacteria trapped within their gut into the human blood stream, spreading the plague.