The past is always present. A group of scientists has managed to extract DNA from the teeth of two people who died during the Justinian Plague in the 6th century, and tests have confirmed that the same pathogen was at the root of the Black Plague of the 14th century, with mutations that are still alive today. The strain that caused the Justinian Plague died out, but a different strain emerged 800 years later to cause the Black Death.
By some estimates, the Justinian Plague led to the deaths of almost half of all human life on the planet. The Black Plague claimed an estimated 50 million lives.
And mutations of Yersinia Pestis can still be a problem:
“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. 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” says Dave Wagner, an associate professor in the Center for Microbial Genetics and Genomics at Northern Arizona University.
The samples used in the latest research were taken from two victims of the Justinian plague, buried in a gravesite in a small cemetery in the German town of Aschheim. Scientists believe the victims died in the latter stages of the epidemic when it had reached southern Bavaria, likely sometime between 541 and 543.The skeletal remains yielded important clues and raised more questions.
Researchers now believe the Justinian Y. pestis strain originated in Asia, not in Africa as originally thought. But they could not establish a ‘molecular clock’ so its evolutionary time-scale remains elusive. This suggests that earlier epidemics, such as the Plague of Athens (430 BC) and the Antonine Plague (165 -180 AD), could also be separate, independent emergences of related Y. pestis strains into humans.
“The tick of the plague bacteria molecular clock is highly erratic. Determining why is an important goal for future research” says Edward Holmes, an NHMRC Australia Fellow at the University of Sydney.
Our response to modern infectious diseases is a direct outcome of lessons learned from ancestral pandemics, say the researchers.
“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,” says Holmes.