Earliest strain of plague bacteria found in neolithic Swedish mass grave

By Dr. Ananya Mandal, MDDec 6 2018

Researchers have unearthed a strain of plague bacteria Yersinia pestis, in a woman who was buried in Sweden during the stone ages. This is one of the earliest strains of plague discovered and the results of the study titled, “Emergence and spread of basal lineages of Y. pestis during the Neolithic decline,” were published in the latest issue of the journal Cell.  

3D illustration Enterobacterias. Gram negativas Proteobacteria, bacteria such as salmonella, escherichia coli, yersinia pestis, klebsiella. Image Credit: Rost9 / Shutterstock

The researchers found a 20 year old woman who belonged to the farming community and was one of the 78 persons who were found in a passage grave in Gökhem in western Sweden. The team undertook genetic tests to look at the possible causes of death. The DNA from her teeth showed the ancient strain of the plague which was dated from around 5,000 years ago. This was also noted in another person buried alongside her. Nicolás Rascovan, a biologist at Aix-Marseille University in Marseille, France, lead author of the study said that a grave with so many individuals could mean that they all died of the plague epidemic. This tomb was of limestone and was dated to Neolithic times he added.

This is considered to be the oldest evidence of plague, according to the researchers. Simon Rasmussen at the University of Copenhagen in a statement said, “This is the earliest strain of the plague that we know about, and it probably played a big role in the decline of the population. You suddenly have this big outbreak and a lot of people are going to die.”

The strain of plague detected at Gökhem is one that causes pneumonic plague explain researchers. This type of plague that affects the lungs commonly, is more severe and rapidly fatal compared to bubonic plague that mainly affects the lymph nodes. Black Death across Europe in the 14th Century killed around 200 million people and that was an epidemic of bubonic plague.

According to Rasmussen the origin of the plague as a disease among humans can be said to have appeared around 6,000 years back in regions that are now Ukraine, Romania and Moldova. These areas were inhabited by tens of thousands of individuals and there was overcrowding, poor hygiene and sanitation and close proximity to animals. All of these led to breeding of pathogens he explained.

The researchers went on to write that plague bacteria first appeared among the Eurasians living in settlements around 5,700 years back. It spread rapidly among populations that were farmers via traders and trading routes. The traders travelled via horse drawn carts and took the microbes with them to far off lands. According to the scientists there was a collapse of these large settlements and plague epidemics could be one of the reasons for such declines. This decline is called the neolithic decline which led to a fall in the European populations around 5,500 years back. Rasmussen explained, “We know that there was this decline in the population in neolithic times and that made it possible for people to migrate into Europe. When that happened, it completely changed the genetic makeup of the early Europeans. It turned Europeans into what they are today.” This movement brought with it the strains of the microbes, the researchers added.