Scientists believe the Black Death, one of the worst infectious disease outbreaks in human history, has left a mark on the immune systems of people living today.
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Four DNA variants appear to have helped boost survival rates during the 14th-century plague, which was caused by the bacteria Yersinia pestis and is thought to have killed up to 60% of the western Eurasian population in just eight years.
Researchers from the University of Chicago, McMaster University in Ontario and the Pasteur Institute in Paris now say that “at least two of those variants associated with surviving the Black Death can be linked to autoimmune conditions common in modern society – including Crohn's disease and rheumatoid arthritis ”, reported The Washington Post.
“Our genome today is a reflection of our whole evolutionary history” as we adapt to different germs, said Luis Barreiro, a senior author of the research.
The Black Death was a 14th-century pandemic of bubonic plague, a disease caused by the bacterium Yersinia pestis. The term is a “reference to the gangrenous blackening and death of body parts, such as the fingers and toes, that can happen with the illness,” said the BBC.
While the plague has been wiped out in most of the world, “cases do continue to occur annually in rural areas of Africa, Asia and even America,” according to Oxford University, which has been working on a vaccine against the ancient illness.
There are three different types of plague: bubonic, pneumonic and septicaemic.
“If left untreated, the bubonic form has a 30 percent to 60 percent fatality rate and the pneumonic form is almost always fatal. Both bubonic and pneumonic plague can develop into a life-threatening infection of the blood called septicaemia,” explained the university.