The earliest known plague outbreak happened in what is now Russia 5,500 years ago. Scientists found the evidence in ancient teeth.

About 5,500 years ago, several dozen hunter-gatherers died near Lake Baikal. DNA from the bacterium that causes plague survived in their teeth. Science journalist Ilya Kabanov, who runs the Telegram channel Laiflong Muki, explains how a study of ancient burial grounds became something of a detective story — and why the discovery changes our understanding of the history of epidemics.