What Made the Black Death so Deadly

Maggie Koerth-Baker reports the pretty amazing fact that if you happened to get infected with Yersinia pestis — the bacterium that caused the Black Plague — today, you would have a 97% chance of surviving even without modern medical care. So why did it kill between 30-50% of Europeans in the 14th century? To find out, scientsts have been looking for ancient plague DNA:

 

In 2011, a team led by McMaster University paleogeneticist Hendrik
Poinar became the first to reconstruct a full genome for Black Death era
Yersinia pestis.

This was not a full and complete genome drawn from a single
bacterium inhabiting the body of a single victim. Instead, the genome
was patched together from bits and pieces of DNA in remains taken from London's East Smithfield cemetery.
The small chunks were lined up to create a whole, similar to the way
you make a panoramic photo by combining a series of different shots.
Hendrik Poinar calls it a "draft" of the genome, rather than a smooth,
polished work of biology.

The draft tells us a couple of things. First, the Y. pestis of the
Black Death era is related to modern Y. pestis. In fact, it's probably
the ancestor of all the strains of Y. pestis that exist today. Second —
and this is the weird part — there is really not much difference between
the old Y. pestis and the new. It boils down to about 100 genetic
changes, few of which seem to have given the bacteria enough of an
evolutionary advantage that they spread widely through the population.

Genetically, Y. pestis has barely changed. Its infection profile in
the real world, though, has changed massively. That suggests that at
least some of those small alterations in the genome must have been
extremely important. But which ones? And why? To answer those questions,
you could reverse-engineer the evolution of Y. pestis in the
lab. "We'd have an opportunity to test those changes, one at a time, and
find out," Poinar said. "… If we could do it in a form or fashion
that wouldn't terrify people."

So, who's going to join me in volunteering to be infected with ancient plague for Science? After all, with modern medical care, there's probably at least an 80% chance of survival. I like those odds!

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