It wasn’t just rats. Body lice may have helped spread bubonic plague.

The bubonic plague pandemic of the 14th century gained infamy as much for its death toll — 25 million in Europe alone — as for the horror of the disease itself. Scientists have long blamed rat-transmitted fleas for the plague’s swift spread. But recent research points the finger at an additional culprit: body lice. A study in the journal PLOS Biology suggests that body lice are capable of transmitting Yersinia pestis, the bacterium that causes plague, more effectively than previously thought. Past research has focused on rodent-borne fleas as a...