How is Black Death still affecting health 700 years later?

A study published on Wednesday in the journal Nature indicates that our mediaeval ancestors may have passed on the genes that once helped them survive the Black Death plague to us, only today these genes are making us more susceptible to certain diseases. 

The study analysed the DNA of centuries-old skeletons and found the mutations that helped people survive the plague that swept through Europe and killed at least 200 million. However, these same mutations are linked to auto-immune diseases including, Crohn’s disease, rheumatoid arthritis and lupus.

These diseases turn the immune system responsible for defending our body against disease and infections on us and start attacking the body’s own healthy tissues. “A hyperactive immune system may have been great in the past but in the environment today it might not be as helpful,” said Hendrik Poinar, an anthropology professor at McMaster University in Ontario and senior author of the study. 

The Black Death was the single deadliest event recorded in human history, the plague had swept throughout Europe, the Middle East and northern Africa and wiped out up to 50% of the population in the 14th century. Researchers theorised that seismic events must have impacted human evolution. Therefore, this study shows how germs shape us over time, said the researchers. 

“Our genome today is a reflection of our whole evolutionary history”, said Luis Barreiro, a senior author of the research in the context of our adaptability to different germs over time. He and his colleagues at the University of Chicago, McMaster University in Ontario and the Pasteur Institute in Paris studied the ancient DNA from at least 200 people from London and Denmark. 

The samples of bones, particularly teeth chosen for this study, were from people who died over 100 years that stretched before, during, and after the Black Death. The samples were collected from East Smithfield plague pits in London which was used for mass burials in 1348 and 1349 as well as some others from Denmark. 

The scientists were able to identify four genes which, depending on the variant either protected against or increased susceptibility to the bacteria that causes bubonic plague. 

The results were confirmed using the plague bacterium, Yersinia pestis and samples of blood were taken from people which showed that the helpful mutations were more able to resist the infection than those without, said a media report. 
Therefore, if a person had the right mutation their likelihood of surviving the plague mostly spread by the bite of an infected flea, was 40% higher, said the study. Today those plague-resisting mutations are more common than they were before the Black Death. 

While past research has sought to examine the effect of the Black Death on the human genome, this study shows the significance the plague had on the evolution of the human immune system, said Barreiro. Furthermore, a unique aspect of this research, he added, was to focus on a narrow time window around the event. 

However, the more recent Covid-19 pandemic will not leave a similar legacy on human evolution said, the senior author attributed this to the much lower death rate when compared to Black Death. 

Additionally, Covid killed more elderly people who already had children or those who were past the point of having them, said Barreiro. Whereas evolution works through a person’s ability to reproduce and pass on the genes and since the bubonic plague killed so many across the age spectrum it had a huge impact, he added.