A Plague On Both Your Houses!

by Shraddha Chakradhar

The famous words by Shakespeare (via Mercutio in Romeo and Juliet) are immortal, and so is, apparently, the plague’s influence. The plague, the Black Death, the one that Mercutio is referring to when he curses the Capulets and Montagues, is still around today. The same one that killed nearly half of the world’s population in the mid-14th century, plus or minus a few changes in the DNA structure. I know this now because I had to write a 600-word story about it this morning. I had between the hours of 9AM and noon to research and write a story about the Black Death. Needless to say, it was nerve-wracking. But I actually had a lot of fun doing it. For one, the topic was fascinating. As I was telling a colleague of mine, “I love medieval Europe and anything related to medieval Europe.” And second, I couldn’t afford to meditate for longer than a few seconds on the construction of a particular sentence. The urgency to get the story done and let little things go was refreshing from my usual routine of obsessing over using one word over another.

Anyway, I am posting my final product here. How do you think I did for 3 hours of work? (Bear in mind, we have thus far been giving a week to do something like this)

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A collaboration of scientists from Germany and Canada has sequenced what they call a “draft” of the genome of Yersinia pestis, the bacterium responsible for the Black Death in Europe. Their paper was published online in Nature on October 12, 2011.

In an interview for NatureVideo, University of Cambridge Historian John Hatcher said, “The Black Death was an epidemic on an unimaginable scale. It swept across Europe in the mid-14th century, killing…up to half of the population, 1 in 2 of the population in a space of 7 years.”

The collaborative team was led by Kirsten I. Bos of McMaster University in Ontario and Johannes Krause of the University of Tübingen in Germany. Using the remains of teeth and bones they found in an ancient burial ground for Black Death victims in East Smithfield outside London, England, the team was able to sequence and reconstruct the ancient DNA of Y. pestis.

Discovered in 1894 by scientist Alexandre Yesin of the Pasteur Institute, Y. pestis has been infecting both human and animal populations for centuries. It originally evolved as a harmless soil-dwelling organism. The pathogenic strain, however, is found in fleas, which spread it to rats, which in turn spread it to human beings. And this pathway was how the Black Death spread so rapidly.

While most people are familiar with the devastating effects of the Black Death, fewer still know that the bacterium continues to infect people today, albeit in a less severe manner. “Although we think of the [Black Death] plague as something that happened a long time ago and [it] decimated European populations then, it’s still very much an ongoing concern, and a very important pathogen today,” said senior editor of Nature Magdalena Skipper in the NatureVideo interview.

In a Nature podcast interview, Johannes Krause said that there were approximately 2,000 cases a year worldwide in countries like the United States and Mexico, parts of Africa, as well as Asian countries such as China and India.

What the researchers were interested to know, Krause revealed in the same podcast interview, was how different current strains of the bacteria are from the ancient strains. What they found was surprising:

“We found almost no difference between the ancient plague and the modern plague strains” said Krause.  The difference was a matter of a few positions in the DNA sequence. These few positions, he elaborated, are ancestral to the modern strain. In other words, all the strains of Y. pestis that affect humans today descended from the ancient plague’s strain.

Why this is surprising is because of the effect that these similar strains have on human populations. The Black Death killed half the existing population, whereas the plague today affects less than 1% of the world’s seven billion population.

The reason for the difference is that medieval Europe was exposed to the plague for the first time when it was “unleashed” according to Krause. They had no prior immunity to protect themselves against it. Other reasons for the severity of the Black Death lie in factors that distinguish the mid-14th century world from the modern world: factors such as difference in climate and environment, as well as social and lifestyle changes.

What we can learn from the study is how quickly a pathogen can wreak havoc on a population that has no previous exposure.

“Paradoxically, society was able to cope much better in the 14th century with deaths on this horrendous scale than we would be able to cope today” said John Hatcher. “Today we have such complex interconnections that anything on that scale today would cause complete chaos.”

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