A team of researchers may have discovered the origin of the bubonic plague which wiped out one-third to one-half of the European population in the Middle Ages.
Scientists from the Max Planck Institute for the Science of Human History analyzed DNA from the bacterium Yersinia pestis found on a pair of skeletons buried together in a single grave in the Samara region in Russia nearly 4,000 years ago, Science Daily has reported.
The DNA revealed that the bacteria found on the two skeletons contained the parent genetic material that resulted in the Black Death–an outbreak of bubonic plague that killed at least a third, and possibly as much as half, of the population of Europe between 1347–1351.
“Both individuals appear to have the same strain of Y. pestis,” commented one of the scientists, Kirsten Bos.
“And this strain has all the genetic components we know of that are needed for the bubonic form of the disease.
“So plague, with the transmission potential that we know today, has been around for much longer than we thought.”
One of the scientists involved in that project, evolutionary geneticist Morten Allentoft, from the Natural History Museum of Denmark, thinks that the plague might have played a part in the mass migration that occured at the time from the steppes–what is now Ukraine and Russia–into Europe and central Asia.
History shows there were such migrations, Allentoft told the Scientific American, “but we didn’t know what the cause of these quite sudden migrations was.”
The form of plague Allentoft’s team discovered lacked the gene that allowed it to live in fleas.
The Y. pestis bacterium causes many varieties of plague, but the three main types were bubonic, which is spread by flea bites; pneumonic, which can spread through inhaling infected saliva (from coughing or sneezing victims); and septicaemic, which is spread through blood.
The bubonic plague was so deadly because fleas had so many potential hosts, from rats to household pets, and people themselves. Stopping the spread of fleas is much more difficult than avoiding the other two vectors.
This latest research proves that both types of plague coexisted, although it remains unclear whether both were equally prevalent.
“Whether the lineages were equally prevalent in human populations, and the extent to which human activities contributed to their spread, are questions that would need further investigation,” explained senior author of the study, Johannes Krause.
“Additional Bronze Age and Iron Age plague genomes could help pinpoint key events that contributed to the high virulence and spread of one of humankind’s most notorious pathogens.”
Plagues caused by the Y. pestis bacterium have killed millions in Europe and Asia, and as recently as the late 1800s, it killed tens of thousands in China.
The plague has not been eradicated. In 2014, Chinese authorities quarantined the city of Yumen in Gansu province after a plague broke out there.