Cracking the Genome of the Black Death

Scientists crack Black Death’s genetic code

By Kate KellandPosted 2011/10/12 at 2:23 pm EDT

LONDON, Oct. 12, 2011 (Reuters) — Scientists have mapped out the entire genetic map of the Black Death, a 14th century bubonic plague that killed 50 million Europeans in one of the most devastating epidemics in history.

A Wayson stain of the Yersinia pestis bacterium, responsible for the plague that ravaged Europe between 1347 and 1351. REUTERS/CDC

The work, which involved extracting and purifying DNA from the remains of Black death victims buried in London’s “plague pits,” is the first time scientists have been able to draft a reconstructed genome of any ancient pathogen.

Their result — a full draft of the entire Black Death genome — should allow researchers to track changes in the disease’s evolution and virulence, and lead to better understanding of modern-day infectious diseases.

Building on previous research which showed that a specific variant of the Yersinia pestis (Y. pestis) bacterium was responsible for the plague that ravaged Europe between 1347 and 1351, a team of German, Canadian and American scientists went on to “capture” and sequence the entire genome of the disease.

“The genomic data show that this bacterial strain, or variant, is the ancestor of all modern plagues we have today worldwide. Every outbreak across the globe today stems from a descendant of the medieval plague,” said Hendrik Poinar, of Canada’s McMaster University, who worked with the team.

“With a better understanding of the evolution of this deadly pathogen, we are entering a new era of research into infectious disease.”

Major technical advances in DNA recovery and sequencing have dramatically expanded the scope of genetic analysis of ancient specimens, opening up new ways of trying to understand emerging and re-emerging infections.

Experts say the direct descendants of the same bubonic plague still exist today, killing around 2,000 people a year.

A virulent strain of E. coli bacteria which caused a deadly outbreak of infections in Germany and France earlier this year was also found to contain DNA sequences from plague bacteria.

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New Light on the Black Death

Molecular Clues Hint at What Really Caused the Black Death

Wynne Parry, LiveScience Senior Writer
Date: 07 September 2011 Time: 12:25 PM ET
A depiction of the black death from a 15th century Bible.

The Black Death arrived in London in the fall of 1348, and although the worst passed in less than a year, the disease took a catastrophic toll. An emergency cemetery in East Smithfield received more than 200 bodies a day between the following February and April, in addition to bodies buried in other graveyards, according to a report from the time.

The disease that killed Londoners buried in East Smithfield and at least one of three Europeans within a few years time is commonly believed to be bubonic plague, a bacterial infection marked by painful, feverish, swollen lymph nodes, called buboes. Plague is still with us in many parts of the world, although now antibiotics can halt its course.

But did this disease really cause the Black Death? The story behind this near-apocalypse in 14th century Europe is not clear-cut, since what we know about modern plague in many ways does not match with what we know about the Black Death. And if plague isn’t responsible for the Black Death, scientists wonder what could’ve caused the sweeping massacre and whether that killer is still lurking somewhere.

Now, a new study using bone and teeth taken from East Smithfield adds to mounting evidence exhumed from Black Death graves and tantalizes skeptics with hints at the true nature of the disease that wiped out more than a third of Europeans 650 years ago.

This team of researchers approached the topic with open minds when they began looking for genetic evidence of the killer.

“Essentially by looking at the literature on the Black Death there were several candidates for what could have been the cause,” said Sharon DeWitte, one of the researchers who is now an assistant professor of anthropology at the University of South Carolina.

Their first suspect: Yersinia pestis, the bacterium that causes modern plague, including bubonic plague.

The speed of plague

In 1894, Alexander Yersin and another scientist separately identified Y. pestis during an epidemic in Hong Kong. Years later the bacterium was given his name. Yersin also connected his discovery to the pestilence that swept Europe during the Black Death, an association that has stuck.

One problem, however, is that compared to the wildfire-like spread of the Black Death, the modern plague moves more leisurely. The modern plague pandemic began in the Yunnan Province of China in the mid-19th century, then spread to Hong Kong and then via ship, to India, where it exacted the heaviest toll, and to San Francisco in 1899, among many other places.

The disease that caused the Black Death is believed to have traveled much quicker, arriving in Europe from Asia in 1347, after the Golden Horde, a Mongol Army, catapulted plague-infected bodies into a Genoese settlement near the Black Sea. The disease traveled with the Italian traders and later appeared in Sicily, according to Samuel Cohn, a professor of medieval history at the University of Glasglow and author of “The Black Death Transformed: Disease and Culture in the Early Renaissance Europe” (Bloomsbury USA, 2003).

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