A team of geneticists has found the first known case of plague on the body of a 20-year-old peasant woman who was buried some 5,000 years ago in Sweden. The strain of the bacteria Yersinia pestis found in the DNA extracted from their teeth presents the same genetic variants that currently make deadly lung plague if it is not treated in time. Another corpse of a twenty-year-old farmer in the same grave of Frälsegården, in the south of the country, also has traces of the pathogen. The authors of the finding believe they are facing the signs of the first great pandemic of humanity.
Some 5,000 years ago, Europe was experiencing a dark period of which very little is known. It's been centuries some immigrants Asians had brought crops and livestock to the continent. By that time, the first cities with up to 20,000 inhabitants had flourished, where people and livestock lived together in a small space with little hygiene. For unknown reasons, at that time there was a sharp decline in the population of between 30% and 60%, similar to what happened in the Middle Ages with the Black Death. Some of the cities were burned and abandoned. It was the end of the stone age.
The plague strain that killed the Swedish girl appeared about 5,700 years ago, according to her genetic analysis, which makes it the closest to the ancestor of all the plague variants that have emerged since then. Geneticists from Sweden, Denmark and France have analyzed the genome of more than a thousand corpses from this era and the later Bronze Age. The results show that "in a very short period of time, 600 years approximately, many strains of plague spread throughout Eurasia, from the southeast of the Russian steppe to Sweden," explains Nicolás Rascován, a biologist at the University of Aix-Marseille and first author of a study published today in Cell about these findings. "We also show that there were no large human migrations that could explain this dispersion, given that we do not see crossbreeding among the different infected populations. Just at the time when we saw the plague spread, great technological innovations arose, such as wheeled transport and animal traction, the ideal means of spreading the pathogen over long distances. It is the first time in the history of humanity that there were simultaneously the right conditions for the emergence of diseases and at the same time their spread over great distances and that is why we think that this was probably the first great pandemic, "explains this Argentine researcher.
The study indicates that the common ancestor of all Y. pestis modern must have appeared somewhere in Eastern Europe. The team proposes as hypothesis that its origin could be in the enigmatic Cucuteni culture, which flourished in the current Moldova, Romania and Ukraine about 5,700 years ago and whose large settlements were pasture of intentional fire. The objective of the team is to try to find DNA in one of these devastated sites to confirm their idea.
After the Neolithic crisis, about 4,700 years ago, a new wave of immigrants arrived: the Yamnaya, a lineage of nomadic herders from the Eurasian steppes that some experts blame invade Europe by blood and fire and almost completely replace local males. The possibility that the yamnaya, they also introduced the Indo-European languages, bring the plague. But the new work shows that the disease had been in Europe for hundreds of years. "We believe that what these people found was a Europe with ghost towns and a population decimated by the plague and other causes," explains Simon Rasmussen, a geneticist at the University of Copenhagen and co-author of the study. "The Yamnaya had a completely different lifestyle, they did not build large settlements, with which they were possibly less vulnerable to the disease of the peasants," stresses the researcher.
Carles Lalueza-Fox, geneticist of the Institute of Evolutionary Biology of Barcelona, studies the genetic mark of the yamnaya and the plague in populations of the Iberian Peninsula. "It was a time of crisis, violence and abandoned settlements that until now had been attributed to other causes, such as the aridification of crops, but this new explanation seems more plausible," he says. The expert points out that thanks to the analysis of ancient DNA found in tombs that had been discarded but was accessible in public databases, the authors of this study have managed to uncover a "pandemic of which until now there was no historical record".
It is the first time in the history of humanity that the conditions for the emergence of diseases and their spread over great distances were given "
The plague bacteria began as an innocuous microbe, the study authors point out. The plagues of the Neolithic and the Bronze Age were probably less virulent than those that produced the worst pandemics, such as that of Justinian in the sixth century –40 million dead– or the medieval black plague that annihilated half of the inhabitants of the big European cities, because they did not have the gene that allows it to be transmitted by fleas –which in turn ride on rats– and other mutations that greatly increased their aggressiveness. It is the same thing that would happen later with smallpox, malaria, Ebola and Zika, and what will happen with the next great pandemic of this century.