Gene helped overcome the Black Death, may put us at risk now

The gene that shielded the body from the bubonic plague may lead to increased risk of autoimmune diseases in the present population.

The second biggest pandemic of plague, the Black Death, wiped out almost half the population of Europe and North Africa. The plague ravaged Europe from 1347 to 1351 and kept reappearing in certain regions for centuries afterwards.

Now, a group of international scientists have analysed DNA samples from the remains of plague survivors and found that some genes produced proteins that shielded the body from the disease. However, those same genes have been linked with increased risk of autoimmune diseases today. 

The Black Death or the bubonic plague is said to have originated in the East. Plague-causing bacteria called Yersinia pestis travelled on the fleas of rats aboard ships heading towards the Mediterranean. From there, it rapidly spread inland and by 1350, it reached the edges of the European continent including Scotland, Scandinavia and the Baltic countries. Rough estimates show that the plague killed 25 million people across Europe.

The study, published in Nature, examined over 500 samples of DNA— focusing on a 100-year time period — from the remains of people who died before, during and after the plague. They extracted samples from individuals buried in London, including the East Smithfield plague pits, and Denmark.

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Having searched for genetic adaptation related to the plague, scientists found that the Black Death was a powerful selection force that altered genetic diversity associated with the immune system.

The study, which comprised researchers from McMaster University, the University of Chicago, the Pasteur Institute and other organisations, found that individuals with two identical versions (alleles) of the gene ERAP2 were 40% more likely to survive the plague than those with the opposite version of the gene, as the ‘protective’ version of the gene fought off the pathogen much more effectively.