The bacterium Yersinia pestis, the same pathogen responsible for the Justinian plague, the black plague of the fourteenth century and the plague of the seventeenth century, was isolated in the DNA of the skull of a hunter-gatherer who lived 5,000 years ago: it is, to all intents and purposes, the oldest dead in plague known to be. Beyond the sad record, what arouses interest is the “profile” of the pathogen-killer, which at the time seemed less virulent and less capable of causing large-scale epidemics, compared to its subsequent evolutions.
An unwanted guest. Several Neolithic communities in Western Europe went through a sharp decline in population around 5,500 years ago, an event that favored the arrival of the peoples of the East and which has been attributed by some historians to a plague epidemic. Traces of the bacterium Yersinia pestis they were in fact found in a woman who died in Sweden 4,900 years ago.
Now scientists at Christian-Albrecht University in Kiel, Germany, have analyzed DNA taken from the teeth and skulls of four people – a woman, a child and two men – found in a prehistoric landfill in Riņņukalns, Latvia, and lived between 5,300 and 5,050 years ago. In the genetic code of one of the two men, an individual of 20-30 years of age, fragments of DNA and proteins compatible with the prolonged presence of the bacterium were found Yersinia pestis in the blood – an infection that led to his death.
The plague of the origins. Not only is man the oldest victim of the plague; the bacterium that affected it is also of long standing, because it separated from all other known strains 7,200 years ago. It is therefore the oldest plague strain ever found. And you can see: its characteristics make it profoundly different from the bacteria that caused large-scale epidemics in the following millennia.
The disease of an individual. The strain in question lacked the genetic characteristics to be carried by fleas, the main vectors of the plague in the fourteenth century. Five thousand years ago, according to the study authors, it Yersinia pestis it was only transmitted from animals to humans: the victim found may have been bitten by a beaver, as the remains of these rodents were found in a nearby river.
Apparently, the bacterium lacked the genetic tools to spread from human to human and cause violent epidemic waves. The team believes it did not cause bubonic plague, which infects the lymph nodes, but an infection of the blood (septicemic plague) or lungs. It was still a disease chronic and widespread, capable of killing individuals but hardly causing a large-scale plague. Not surprisingly, out of four people buried nearby, only one was sick, and the burial had taken place with care, not in the haste of a health emergency.
The “against” rumors. But not everyone agrees with these conclusions. Simon Rasmussen, a biologist expert in human and bacterial genomics at the University of Copenhagen, continues to believe that the plague was the main cause of the decline of Neolithic civilizations 5,500 years ago. The death of the man found in Latvia is actually part of that period, characterized by large human settlements, migrations and trade, interactions that could have favored the spread of the pathogen.