Study Reveals How the Plague Became Less Deadly and Duration Extended

Recent research has shed light on the evolution of the bacteria responsible for the plague, demonstrating that over centuries, the pathogen became less lethal while its pandemics persisted for longer periods. The study analyzed ancient samples of Yersinia pestis from three major plague outbreaks—the Justinian plague of the 500s, the Black Death of the 1300s, and the ongoing third pandemic beginning in the 1850s—finding a clear trend: the bacteria's genes evolved to reduce their virulence over time.

This decrease in virulence meant that infections caused by the bacteria were less severe, which paradoxically allowed the pandemics to last longer. The less deadly the infection, the more opportunities it had to spread among populations. Researchers confirmed this by infecting rats with contemporary plague samples, observing that the disease persisted longer when its virulence was diminished.

Today, antibiotics effectively treat the plague, but understanding the bacteria's historical evolution provides insights into pathogen adaptation. "This knowledge helps us grasp how pathogens adapt to different circumstances, which is crucial for managing future outbreaks," explained microbiologist Javier Pizarro-Cerda of France's Pasteur Institute. The findings highlight the importance of studying the genetic changes of pathogens to improve our preparedness and response to infectious diseases.

For more details, the study was published in the journal Science and can be reviewed here.