It all began with a harmless intestinal bacterium, which caused little discomfort in humans. But two gene changes were enough and Yersinia pestis became one of the deadliest diseases in the world - the plague was born.
In the 14th century alone, about 50 million Europeans died from the Black Death. But where did the pathogen, which in some cases killed up to 60 percent of the population in the so-called second plague pandemic, come from?
The origin of the pandemic between the 14th and 17th century was evidently a single strain of pathogens, according to researchers from the Max Planck Institute for the History of Mankind in Jena in the journal Nature Communications. "These results indicate that Yersinia pestis reached Europe from the East," says study author Maria Spyrou.
The plague genome was in the teeth of the dead
For the analysis, the researchers had examined the teeth of 34 plague victims from across Europe, they came from England, France, Germany, Russia and Switzerland. In the teeth, pathogens are often deposited, while at the same time genetic material is particularly well preserved - even that of the plague.
In the lab, researchers were able to isolate and analyze the pest genes. The comparison showed that the individual strains were remarkably similar and all originated from an origin. In the study, he was traced back to two individuals found in Laishevo, a place in what is now the Volga region of Russia. The researchers can not say whether the pathogen was created here.
When the plague reached Europe, two strands developed. The disease ebbed away again and again. According to a previous genetic study, the pest has more commonly passed from rodents to humans throughout history, triggering pandemics. However, it is not certain in which host he has survived for so long, possibly fleas.
Other analyzes, however, assume that the bacteria were repeatedly introduced to Europe via Central Asia. The current study did not provide any new evidence for this theory, but it does not exclude it. Perhaps the plague spread across both ways in Europe.
There are still variants of the bacterium worldwide. However, the strains studied now seem to be extinct. At least no current pathogens of this line are known. A big pandemic is unlikely anyway today, because the pest control can be combated with antibiotics.
The two extinct pestle strains have both had mutations in a part of the genome that control how contagious the bacteria are. The researchers now want to clarify whether the genetic changes could have ensured that the pathogens eventually died out.
Previous genetic analyzes have shown that the plague has been plaguing humanity for thousands of years. The oldest proven pathogens date back to the Bronze Age and are 5000 years old. At that time, however, he was not that dangerous to humans. It is not until the first millennium BC that the pathogen apparently makes use of fleas as intermediaries and triggers the dreaded bubonic plague on humans.