Scientists have found evidence of the oldest known plague, dating back about 5,500 years ago — some 200 years earlier than previously thought. Rare, modern-day plague persists and is treated with antibiotics. Researchers found ancient DNA from the plague-causing bacteria in teeth from remains buried in four Siberian cemeteries. They tracked the family dynamics of how and when people got sick and dated the oldest outbreak to around 5,500 years ago, affecting a small community of hunter-gatherers. The new research published Wednesday in the journal Nature shows that the prehistoric plague was just as deadly as the bubonic plague, which spread through Europe, the Middle East and northern Africa.