A person in Arizona recently died of pneumonic plague—a rare and severe form of the disease. An expert explains how the bacteria that spurred the Black Death centuries ago continues to claim lives

A sudden death caused by the pneumonic plague has caused a stir. Previously known to be the cause of bubonic plague, people are expressing their concern regarding the contagious disease and how did it come back.

Pneumonic plague is both “the least common and most dangerous type of plague,” according to the Cleveland Clinic.