Cause of the Most Devastating Pandemics in History Revealed

A new study reveals that two of the world's most devastating pandemics, the plague of Justinian and the Black Death, were caused by distinct strains of the same pathogen.

Researchers at McMaster University (Hamilton, ON, Canada), Northern Arizona University (Flagstaff, USA), the University of Sydney (Australia), and other institutions isolated miniscule DNA fragments from the 1,500 year old teeth of two victims of the Justinian plague, who were buried in the Aschheim-Bajuwarenring cemetery (Bavaria, Germany); these are the oldest pathogen genomes obtained to date. Using these short fragments, the researchers reconstructed the genome of the bacterium responsible, and compared it to a database of genomes of more than a hundred contemporary strains.

The results showed that the bacterium was a strain of Yersinia pestis, the same pathogen responsible for the Black Death. But while the strain responsible for the Justinian outbreak was an evolutionary “dead-end” and faded out on its own, the other, likely a descendant of the Black Death strain, lead to another worldwide pandemic spreading from Hong Kong across the globe in the late 1800’s. According to the researchers, these findings suggest a new strain of plague could emerge again in humans in the future. The study was published online on January 28, 2014, in the Lancet Infectious Diseases.

“About 200 rodent species carry the plague and could potentially infect other animals or humans. Scientists need to sharpen their surveillance of plague in rodent populations to try averting future human infections,” said lead author Associate Professor Hendrik Poinar, PhD, director of the McMaster Ancient DNA Center. “If we happen to see a massive die-off of rodents somewhere, then it would become alarming. Plague is something that will continue to happen, but modern-day antibiotics should be able to stop it.”

The Plague of Justinian struck in the sixth century and it is estimated to have killed between 30 and 50 million people—virtually half the world's population—as it spread across Asia, North Africa, The Arabian peninsula, and Europe. The Black Death struck some 800 years later with similar force, killing 50 million Europeans in just four years (1347-1351).

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