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Arizona Scientists Pinpoint Birthplace of Plague


Northern Arizona University biologists have pinpointed the source of one of the deadliest plagues of all time. The discovery not only solves some ancient mysteries about the first pandemic, but could also provide answers in the event of a bioterrorism threat.

Their results were just published in the peer-reviewed scientific journal PLOS Pathogens.

First a brief history lesson: There were three pandemics associated with plague. The most recent began around 1850 and it’s still killing people in some places today. The second one going back in time began in the 14th century and included an epidemic called the Black Death that wiped out about 20 percent of Europe’s population. The oldest pandemic started in the 6th century (about 1,500 years ago) and likely caused the fall of the early Roman Empire.

We didn’t know much about it until recently when Northern Arizona University biologist Dave Wagner got involved.

"I started working on plague because we have it here in northern Arizona in native ground squirrels," Wagner said.

About five years ago he changed his focus from squirrels to humans. Wagner and some other scientists mapped out what they call the global family tree of plague to show how it spread around the world.

At about the same time some homebuilders developing a new subdivision in Munich dug up some ancient skeletons. By German law they have to stop and let archaeologists inspect the remains.

"They found certain burials where it wasn’t just a single individual, it was multiple individuals in the same grave," Wagner said. "And traditionally that’s thought to be indicative of an infectious disease coming through and killing a large number of people."

The skeletons were about 1,500 years old so the best way to find DNA was in their teeth. German scientists ground down the teeth, extracted the DNA, then Wagner and his colleagues isolated and studied the DNA.

"Now most of the DNA that’s going to come out of that tooth is human DNA and so we were sort of looking for a needle in a haystack. We’re looking for plague DNA inside all that human DNA," Wagner said.

And keep in mind that it’s ancient DNA, so it’s been degraded and fragmented over time.

Biologist Dawn Birdsell was the one who first confirmed the teeth had the plague bacterium called yersinia pestis. She couldn’t wait to tell Wagner.

"I was extremely excited," Birdsell said. "It was very late at night though, so Dave was asleep. But he got the email at 4 in the morning when he wakes up."

They then repeated the process several times in different labs to ensure the results were the same. The Arizona and German scientists confirmed the plague bacterium caused the first pandemic. Their discovery dispels many other theories. The team then took their study a step further using molecular technology to develop a DNA fingerprint. This enabled them to locate the likely source of the first pandemic to China where they found a similar strain.

"Plague perhaps like maybe no other disease has changed the course of human history multiple times," said David Engelthaler, director of programs and operations at TGen North in Flagstaff. So what these researchers found really advanced our understanding of the history of plague. It’s also helped explain the human history as well so it’s fairly significant.

Now you may be wondering why we don’t see major pandemics today. Two reasons: Our hygiene has improved and we’ve cleaned up our cities. And Dave Wagner says antibiotics pretty much take care of the first sign of plague.

"But in places where those things aren’t as well established, for example Madagascar and other places in Africa, there’s still hundreds if not thousands of human cases every year," Wagner said.

Plague may not be an infectious disease that many people are concerned about today but the Department of Homeland Security, or DHS, has been very interested in these results. Wagner says if there was a bioterrorism event, the agency would want to detect it quickly and develop a DNA fingerprint to determine the source.

"And so we see this as the ultimate validation of those approaches that we’ve developed for DHS," Wagner said. "Because if you can do this on a strain from 500 A.D. then you should be able to do it on contemporary material that might be used in a bioterrorism event."

Wagner and his team’s next step is to piece together the genome to try to learn what made the strain so deadly.