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Plague Why the plague became so deadly
The dangerous infectious disease Pest has accompanied mankind for thousands of years and has repeatedly led to devastating epidemics with millions of deaths in the past. Now, researchers have discovered that the plague pathogen has existed for much longer than previously thought. This was in a harmless form apparently already in the Bronze Age among the people spread.
"Black Death" is one of the worst epidemics in history
The plague is one of the most devastating epidemics in human history and led to severe epidemics, especially in the Middle Ages. However, the infectious disease, also known as "black death", apparently occurred at least 3,000 years earlier than previously thought. Because like an international research team led by Eske Willerslev from the University of Copenhagen in the journal "Cell"
shows, the pathogen can be traced back to the Bronze Age almost 5000 years ago.
Pest virus: what made the plague so deadly. Image: Giovanni Cancemi - fotolia Bubonic plague is usually caused by stings of infected fleas
However, it can be assumed that the plague bacterium Yersinia pestis was initially not a major threat to humans, the scientists report in a press release by the publisher "Cell Press". Instead, it was only in the first millennium BC that it used the opportunity to use fleas as a transmitter. Actually, the plague is a disease of wild rodents such as mice, rats or squirrels. But even their parasites can carry the pester in itself and spread by stitches under the rodents.
In this way, people can also be infected with the so-called "bubonic plague": The flea stings an infected host, picks up the plague bacterium and passes it on another stitch. As a result, a transfer from one person to another is also possible, which can quickly lead to a dangerous epidemic or pandemic. A plague septicemia can also occur when bacteria enter the bloodstream through a flea sting. The pneumonic plague, on the other hand, is usually passed on from person to person by droplet infection.
Researchers find traces in examined teeth
The researchers had examined the teeth of 101 people for genetic traces of the bacterium Yersinia pestis, which came from excavations or museums, according to the release. The individuals lived mostly in the Bronze Age in Europe and Asia. In seven cases, the scientists were finally able to prove the pathogen, which were people who had lived between 2794 and 951 BC. The first historically proven pandemic to date is the "Justinian Plague", which extended from Constantinople in the years 541-767 through numerous Mediterranean ports to the Rhine.
"Protective gene" detectable only from the year 951 before Christ
In order to understand the development of the bacterium, the researchers then examined 55 specific genes, which are of central importance in the pathogenic properties of the bacterium. The result: The so-called "ymt gene" could not be detected in the found early pest irritant, by which the pathogen is otherwise protected in the intestine by fleas. Accordingly, the scientists would assume that Yersinia pestis was not initially transmitted via parasites, the report says. Since the ymt gene was detected only from the year 951 before Christ, probably only the later form of the plague bacterium used fleas as an intermediate host to trigger the disease.
Although the early form of the pathogen was less dangerous in comparison, the researchers may be responsible for the large scale population movements in the Bronze Age in Europe and Asia, scientists suggest. Because people could have fled the outbreaks of the disease or repopulated areas where an epidemic had previously claimed many victims.
Pest claims 50 million deaths in the 14th century
The spread of the pathogen then took place quickly. From the first millennium BC, the formerly relatively harmless bacterium finally developed into one of the deadliest pathogens humanity has ever faced, explain the scientists. For in the 14th century alone, the plague fell victim to about 50 million people, the World Health Organization (WHO) estimates.
"The study changes our view of when and how the plague affected human populations and opens up new opportunities to study the evolution of disease," said study lead Willerslev. "In addition, our study changes the historical understanding of this extremely important human pathogen and makes it possible that other so-called epidemics such as the plague of Athens and Antonine could have been caused by Yersinia pestis," adds co-author Simon Rasmussen of the Technical University Denmark in Lyngby.
Left untreated, the plague is usually deadly
The infectious disease, however, is still not defeated today, but is still locally limited, especially in Africa (e.g., Madagascar, Congo), Asia (e.g., Russia, Kazakhstan, India), and America (e.g., Peru, southwestern US). If the disease is not treated in time with antibiotics, it is usually fatal. In 2013, according to the WHO, of 783 people worldwide, 126 were killed.
"The underlying evolutionary mechanisms that have enabled the evolution of Y. pestis are still effective today. And to learn more about it will help us to understand how future pathogens can develop or how their dangerousness can increase, "says Simon Rasmussen (nr)