• Scenes from an earlier outbreak of bubonic plague

The heyday of the bubonic plague ended about 400 years ago, but that doesn’t mean the disease doesn’t still exist. [Insert noise of impending doom here.] There are between 1,000 and 3,000 cases worldwide per year—a mere drop in the bucket compared to the 75 to 200 million during the Black Death of the Middle Ages—and scientists, in particular Wyndham Lathem, a professor of microbiology-immunology at Northwestern’s Feinberg School of Medicine, are curious about what made the disease tick.

So Lathem and his colleagues are tracking the evolution of bubonic plague, in particular Yersinia pestis, the bacteria that causes it.

“We want to see if it’s gotten more or less deadly over time,” he says. “Was the strain from the 1350s anything close to what we have now, or was it an offshoot? So many people died. Maybe the old strain, the one that was superdeadly, doesn’t exist.”