Scientists say that the Black Death, the bubonic plague which killed 75 to 200 million people when it struck in the 1300s, and the Plague of Justinian that killed up to 5,000 a day at the height of its pandemic, were caused by different strains of the same bacteria and have warned of a possibility that new strains of the bacteria could strike in the future.
In a new study published in Lancet Infectious Diseases, Jan.28, researchers extracted bits of DNA from the teeth of two German victims who were killed by the Justinian plague 1,500 years ago, and used these to reconstruct the genome of the plague's pathogen, Yersinia pestis. The researchers then compared this with 131 other strains of Y. pestis in the database of other plagues including the Black Death and those that occurred in the 19th century and found this to be distinct.
"We conclude that the Y pestis lineages that caused the Plague of Justinian and the Black Death 800 years later were independent emergences from rodents into human beings," the researchers wrote.
The researchers were also stumped as to why the plague suddenly died out. "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?" said study lead author Hendrik Poinar, director of the Ancient DNA Centre at McMaster University in Canada.
Jeremy Austin, from the Australian Centre for Ancient DNA, explained the implication of the study's findings. "It certainly tells us that these catastrophic diseases aren't things that evolve once, and then lurk around waiting for an opportunity to reappear - they actually evolve multiple times from different ancestors," he said. "Which makes it very much harder to predict when they're going to happen next, and how they evolve and therefore how you might prevent them happening."
Dave Wagner, professor in the Center for Microbial Genetics and Genomics at Northern Arizona University also warned there could be a future outbreak. "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," he said. "If the Justinian plague could erupt in the human population, cause a massive pandemic, and then die out, it suggest it could happen again."
Experts, however, believe modern plague epidemic would not be as devastating. "Plague is something that will continue to happen but modern-day antibiotics should be able to stop it," Poinar told the Associated Press.
Poinar also said that doctors should be vigilant. If the plague transforms into an airborne version, Pionar warned, it would be difficult to arrest the spread of the bacteria because it can reach the lungs and its droplets can easily spread by coughing. Such an eventuality can kill people within 24 hours of being infected.
The scientists, Poinar added, should keep a close watch on the rodent population as they are known carriers of the plague.
The research was funded by McMaster University, Northern Arizona University, Social Sciences and Humanities Research Council of Canada, Canada Research Chairs Program, US Department of Homeland Security, US National Institutes of Health, Australian National Health and Medical Research Council.
