Australasian Science: Australia's authority on science since 1938

DNA Reveals How Plague Spread

DNA fragments from 1500-year-old teeth have revealed that two of the world’s most devastating plagues were caused by distinct versions of the same bacteria.

The research, by an international collaboration of scientists, examined DNA fragments from the 1500-year-old teeth of two victims of the Plague of Justinian, and produced the oldest pathogen genomes ever obtained.

The dental samples came from ancient plague victims buried in a small cemetery in the German town of Aschheim, who are believed to have died in the final stages of the Justinian epidemic when it reached southern Bavaria between 541 and 543.

The scientists reconstructed the pathogen’s genome and compared it with a database of more than 100 contemporary Yersinia pestis genomes. “We discovered that the bacterium responsible for the Plague of Justinian, which jumped from rats to humans and killed many millions of people in the sixth century, faded out on its own,” said Prof Edward Holmes of the University of Sydney, who was co-lead author of the study published in Lancet Infectious Disease.

Little has been known about the origins or cause of the Plague of Justinian, which helped bring an end to the Roman Empire, killing virtually half the world’s population as it spread across Asia, North Africa, Arabia and Europe.

The study concluded that the Justinian outbreak was an evolutionary “dead-end” that was distinct from strains involved in the Black Death and other plague pandemics.

“This study raises intriguing questions about why a pathogen that was both so successful and so deadly died out. One testable possibility is that human populations evolved to become less susceptible,” Holmes said.

The findings not only give a new historical perspective but could lead to a better understanding of the dynamics of modern infectious disease.