Scientists reconstruct Black Death DNA - ABC Online

ELEANOR HALL: Now to our story about the scientists who've reconstructed the genetic code of the germ behind the Black Death. The team extracted fragments of DNA from the teeth of four plague victims buried in East London about 700 years ago.

The plague killed around 50 million people when it swept through Europe between 1347 and 1351. The scientists say mapping it will help them understand modern day pathogens, as Ashley Hall reports.

ASHLEY HALL: To extract the secrets of the Black Death, the researchers headed first to a grave site known as a plague pit in East London. There, they found medieval corpses, with their teeth intact.

HENDRIK POINAR: Teeth actually turn out to be one of, a couple of good sources of ancient DNA. The teeth, actually the enamel is quite good at preserving the DNA so it is a bit of time capsule so to speak.

ASHLEY HALL: Associate Professor Hendrik Poinar is a co-author of the study that's been published in Nature magazine. He's a specialist in anthropology and infectious diseases at McMaster University in Ontario.

HENDRIK POINAR: And within the root pulp where of course connective tissue and blood is of course fed into the tooth as it grows, there actually the blood-borne pathogen sat for the last 660 years.

ASHLEY HALL: So they drilled into the teeth, and found enough DNA fragments to identify the pathogen that caused such devastation. It is known as Yersinia pestis.

HENDRIK POINAR: This particular sequence is the ancestor or great grandmother if you wish, of all the modern pestis-circulating pathogens today. So all the plague outbreaks we see across the globe today have their origins in medieval Europe in the 1340s and '50s.

We have a set of changes in this ancient one that we don't yet know, we don't find a smoking gun I guess is the easiest way to say it. We don't see a smoking gun that could immediately allow us to identify a punitive change in the virulence.

That being said we don't know since we haven't reconstructed the proper order that the genes sit on this genome, whether or not that order and this constellation of changes we find might actually have induced greater virulence and been so nasty.

ASHLEY HALL: Hendrik Poinar says the plague terrorised the population.

HENDRIK POINAR: For most people it was the end of the world and it was the apocalypse and everything was coming to a crashing end, the rains and no food and this massive infection. I mean, it is very hard for us to imagine a third or a half of a population in a city like London collapsing.

ASHLEY HALL: Monash University's Professor Constant Mews is a medieval historian.

CONSTANT MEWS: There is a wonderful description in the beginning of Boccaccio's Decameron which is a collection of stories where he sets the storytelling among a group of men and women who want to escape from the plague and he has a wonderful eyewitness account and he describes three different responses.

Some people completely panicked and shut themselves up and others said well look, we may as well make great fun and enjoy ourselves because tomorrow we are going to die and then a few people who were more cautious and tried to sort of find a balance between those two ways.

ASHLEY HALL: Nonetheless, survivors of the plague did identify ways to keep themselves safe, as another of the study's authors, Professor Johannes Krause from the University of Tubingen explains.

JOHANNES KRAUSE: They knew that you shouldn't be close to a plague victim when it dies because when the body temperature falls below 35 degrees, all the fleas are leaving the body. They are kind of looking for a new host so that is kind of the moment when the risk of infection is the biggest.

And people are actually seen the medieval age that doctors get much more infected by the plague than for example and the grave diggers because the moment the person dies this is really when the fleas are leaving the sinking ship if you want.

ASHLEY HALL: The infection still kills 2000 people a year, raising the question of how safe it is to replicate the pathogen's DNA. What would happen if the code fell into the wrong hands? Professor Poinar says that's not a concern, because modern medicine would make short work of the ancient pathogen

ELEANOR HALL: Ashley Hall reporting.