Genomics Reconstructs DNA of the Black Death

The bacterium Yersinia pestis decimated almost 50 percent of Europe’s population from 1347-1351 in what is now referred to as the Black Death. It also left a legacy of current pestis strains, creating small outbreaks of plague throughout the world.

Today with the advancement of genomics technology, scientists have mapped the entire DNA sequence of the pestis to increase understanding of pathogen evolution and adaptation for re-emerging infections as well as to explain exactly why the ancient bacterium was so deadly.

According to historians, pestis travelled from China over to Europe on the Silk Road trading route. Fueled by a fresh population of hosts, the bacterium spread like wildfire throughout Europe, inflicting a illness-related death toll unmatched so far in human history.

“Italian chroniclers said at the time that the living were scarcely able to bury the dead,” said John Hatcher, historian from university of Cambridge, to Nature Magazine. During the Medieval Era, rats spread the Black Death to humans, and today strains of pestis continue to transfer between rodents and humans, producing around 2,000 cases of plague throughout the United States and the world each year.

A team of researchers led by German scientist Johannes Krause, from the University of

Genomics, the study of genes and their function, has had massive implications for research into ancient pathogens.

Tubingen, Germany, extracted pestis-infected living tissue inside the teeth of four Black Death victims buried at the East Smithfield cemetery in London, England. The scientists then sequenced Yersinia pestis, producing a total of 2,366,647 high-quality chromosomal reads with an average DNA fragment length of 55.53 base pairs.

By reconstructing a draft of the Y. pestis bacterium, Krause and his team revealed that the Black Death is the likely cause for its widespread distribution into the human population. The DNA reconstruction also showed that Y. pestis has close relatives in the 21st century that are emerging in the world.

While no current strain of Yersinia pestis is exactly like the one that killed more than 30 million people over 660 years ago, Krause and his team have found very little difference in the strains living on earth today. This lack of difference in both the ancient and the modern strains of Yersinia pestis support his notion that factors such as environment and host susceptibility may actually have been the key to Yersinia pestis’ widespread.

“We have antibiotics today that can cure the plague. People don’t actually die from the plague today,” says Krause in Nature Magazine’s podcast. What Krause suspects right now is that the reason the plague was so lethal during the Medieval Era was because it was the first occurrence of that strain of pestis, and the people were not adapted at that time to handle the bacterium.

For future outbreaks, Krause is not particularly worried about the current strains of plague because available antibiotics can handle it. The big worry that he and his team see is how the pandemic of Yersinia pestis in the 14th century derived from it having never occurred in the European population before.

According to Krause, the genomics of Y. pestis and its modern strains should be at the forefront of epidemiological discussions to better understand potential outcomes and outbreaks of emerging pathogens.

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