January 28, 2014
Pathogen Responsible For Two Historical Plagues Could Re-emerge
[ Watch the Video: Pathogen Behind Ancient Plagues Could Come Back Someday ]
Brett Smith for redOrbit.com - Your Universe Online
Both the Plague of Justinian in 541 and Black Death some 800 years later were responsible for widespread fatalities across Europe. Now, new research in The Lancet Infectious Diseases journal has found that both pandemics were caused by different strains of the same pathogen.
The international team of study authors also concluded that a new strain of plague could emerge in the future.
"The research is both fascinating and perplexing, it generates new questions which need to be explored, for example why did this pandemic, which killed somewhere between 50 and 100 million people die out?" asked Hendrik Poinar, an investigator with the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University in Canada.
The Plague of Justinian is thought to have played a large role in the fall of the Roman Empire as it killed an estimated 30 to 50 million people across Asia, North Africa, the Middle East and Europe. In the 14th century, Black Death would have a similar devastating effect – killing 50 million Europeans between 1347 and 1351.
Using state-of-the-art processes, the study team isolated small DNA fragments from the 1,500-year-old teeth of two victims of the Justinian plague, interred in Bavaria, Germany. Utilizing brief DNA fragments, they reassembled the genome of a strain of Yersinia pestis, the bacterium behind the plague, and compared it to a repository of genomes containing over a hundred contemporary strains of the pathogen.
The researchers found that the strain behind for the Justinian outbreak was essentially an evolutionary cul-de-sac and was unique from strains that would evolve later and eventually cause the Black Death and other plague pandemics – such as a historical pandemic that spread out from Hong Kong.
"We know the bacterium Y. pestis has jumped from rodents into humans throughout history and rodent reservoirs of plague still exist today in many parts of the world,” said Dave Wagner, an associate genetics professor at Northern Arizona University. “If the Justinian plague could erupt in the human population, cause a massive pandemic, and then die out, it suggest it could happen again. Fortunately we now have antibiotics that could be used to effectively treat plague, which lessens the chances of another large scale human pandemic.”
The researchers noted that the study’s skeletal remains from victims of the Justinian plague yielded significant clues and inspired more questions.
While the researchers now believe that the Justinian Y. pestis strain started in Asia, not in Africa as previously believed, they could not ascertain a 'molecular clock,' so its evolutionary time-scale continues to be elusive. The team said previous epidemics, like the Plague of Athens (430 BC) and the Antonine Trouble (165 -180 AD), could also be different, individual emergences of relevant Y. pestis strains.
"The tick of the plague bacteria molecular clock is highly erratic. Determining why is an important goal for future research" said study author Edward Holmes, an evolutionary biologist at the University of Sydney.
"This study raises intriguing questions about why a pathogen that was both so successful and so deadly died out. One testable possibility is that human populations evolved to become less susceptible," he added.
"Another possibility is that changes in the climate became less suitable for the plague bacterium to survive in the wild," Wagner said.