Half of Europe’s population was wiped out and society as a whole was disrupted.
The plague bacterium Yersinia pestis was around in Europe between 1347 and 1353 and is known as one of the greatest killers of all time.
And now scientists in the Nature magazine that the bacterium has also left a lasting mark on our genetic material, making diseases such as rheumatoid arthritis, diabetes and chronic intestinal inflammation more common today.
Plague cemeteries studied
In the new study, the scientists combed through as many as 516 samples of ancient DNA, taken from the bones and teeth of people who died before, during or shortly after plague outbreaks in London and Denmark, respectively.
One of their theories was that the bubonic plague caused significant changes in the development of our immune system during its deadly journey through Europe, Asia and Africa. And they were right.
In the genes that regulate the immune system, the researchers found four genetic variations that either protected against Y. pestis or increased susceptibility to it. For example, the changes determined who survived the pandemic and who did not.
Genes strengthen soldiers of the body
They found the most striking change around the gene ERAP2, which ensures that the immune system can detect and fight infections.
This is done by the immune system’s ‘scavengers’, macrophages, which ingest and digest viruses and bacteria. The macrophages then cut up the bacteria and take them to the B and T cells of the immune system, so that they can attack. It works a bit like an alarm system.
The new study shows that people with two identical copies of the ERAP2 gene were 40 percent more likely to survive the plague than those who didn’t.
Higher risk of serious diseases
The survivors could therefore also pass these changes on to their descendants, who then had an advantage in later pandemics.
But while the genetic variations in the Middle Ages served mainly as a defense against the common plague, today the same changes can increase the risk of autoimmune diseases such as rheumatoid arthritis, diabetes and chronic intestinal inflammation, where the immune system attacks the body’s own tissues. That is what the researchers write in their report.
Research leader Hendrik Poinar of McMaster University in Hamilton, Canada, compares the two copies of the ERAP2 gene with scissors that cut up bacteria and viruses.
In the Middle Ages, such scissors were crucial to the survival of the individual, while now paradoxically they can have a harmful side effect.
‘The genes you got from your ancestors for surviving the Black Death date back to a time when infectious diseases were a major threat. But now the overactive scissors see your own tissue as an enemy and attack it,” he says MailOnline.