MARY LOUISE KELLY, HOST:
All right. The ongoing Ebola outbreak is an example of how a disease can jump from animals to humans and then spread through a population. A new study looks at one of the most prolific pathogens in human history - the plague. And as NPR's Nate Rott reports, it rewrites the history of that deadly disease.
NATE ROTT, BYLINE: This new study starts with a bit of a mystery that archaeologists uncovered near the oldest and deepest lake in the world, Lake Baikal in southern Siberia. The region is dotted with cemeteries of prehistoric humans, hunter-gatherers who would return to a site to bury their dead over hundreds of years. But one site didn't match what archaeologists were finding at others.
RUAIRIDH MACLEOD: It was kind of a real outlier because the first thing that you noticed was a real excess mortality of kind of kids, of young adolescents and children.
ROTT: Ruairidh Macleod is a post-doctoral researcher at the University of Oxford and the lead author of the new study.
MACLEOD: Most other cemetery sites, you see more like a normal distribution of mortality. So a peak towards mid 20s, when people are doing risky things.
ROTT: There was no evidence of violence, either.
MACLEOD: And they found that it was a super tight time period in which everybody died. So this was also really, really unusual for Lake Baikal.
ROTT: Macleod, who focuses on ancient DNA, wanted to see if there were any clues hidden in their genomes. So using small amounts of their more than 5,000-year-old teeth, where DNA can survive for thousands of years, he reconstructed their genomic data.
MACLEOD: And we decided to compare the data against a large reference database for lots and lots of different pathogen species. And that was when we found this really exciting result that quite a lot of these people had plague DNA in their remains as well.
ROTT: The plague is caused by a bacteria, Yersinia pestis. It's best known for the devastation it wrought through Europe in the 14th century during the Black Death and centuries earlier during the Roman Empire. But this bacteria Macleod and his colleagues describe in the journal Nature was different. It lacked a specific gene that made later plagues so deadly, but it had a super antigen that later strains lacked.
MACLEOD: And what super antigens do is that they cause kind of mass immune system response, and that triggers ultimately cytokine storm and toxic shock syndrome and then death.
ROTT: There are still many questions about the evolution of the plague and where it came from. The researchers say it likely originally spread from marmots, ground squirrels. Taylor Hermes, an anthropologist at the University of Arkansas who was not involved in the new paper, is studying how it may have moved from wild animals to humans to even livestock. And he says this new finding that the plague was moving through hunter-gatherer societies is a powerful reminder.
TAYLOR HERMES: That it's not just big agricultural societies that are sort of like these cesspools for disease.
ROTT: That has long been the dominant theory when talking about infectious disease. He says this new study shows...
HERMES: People of all different scales can cause environmental disruption and bring things out of these environments that can have long-standing impacts even to this day.
ROTT: A lesson worth remembering, he says, in our globalized society.
Nate Rott, NPR News. Transcript provided by NPR, Copyright NPR.
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