The Black Death, the single greatest mortality event in recorded history, left a huge impression on the makeup of genes that code our immune systems. Centuries later, certain genetic variants related to surviving the Black Death continue to influence people's risk of disease and health.
In a new study, an international team of scientists analyzed over 500 ancient DNA samples extracted from people who died before, during, or shortly after the Black Death outbreaks in London and Denmark.
Caused by the bacterium Yersinia pestis, the Black Death was a cataclysmic bubonic plague pandemic that devastated Western Eurasia and North Africa between 1346-52 BCE. Hundreds of millions of people were killed, most prominently in Europe where up to 50 percent of the population may have perished.
In this latest study, researchers discovered that genetics played an important role in determining who lived and who died during the devastating disease outbreak. Among the bodies found in both London and Denmark, they found four genetic variants that either protected against or increased susceptibility to Y. pestis.
The most significant was a single gene known as ERAP2. It's estimated that people with two identical copies of the particular gene were over 40 percent more likely to survive the plague than those who did not because functional ERAP2 helps the immune system recognize the presence of an infection.
As such, it’s apparent that this ferocious pandemic acted as a strong selective pressure that guided the future evolution of the human immune system.
“The selective advantage associated with the selected loci are among the strongest ever reported in humans showing how a single pathogen can have such a strong impact to the evolution of the immune system,” Luis Barreiro, study author and professor in Genetic Medicine at the University of Chicago, said in a statement.
Even in modern populations, the same gene variant still has a strong influence on our immune system and appears to be linked with increased susceptibility to autoimmune diseases, such as Crohn’s disease. While a hyper-charged immune system may have helped you survive the Black Death, it looks like it can cause its own problems when it comes to autoimmune disease, whereby the body's immune system mistakenly attacks its own healthy cells.
The study authors say their work highlights how past pandemics continue to shape the health of people, long after the disease is quashed, contained, or eradicated.
“Diseases and epidemics like the Black Death leave impacts on our genomes, like archeology projects to detect,” explained Hendrik Poinar, PhD, Professor of Anthropology at McMaster University and co-senior author of the study.
“This is a first look at how pandemics can modify our genomes but go undetected in modern populations. These genes are under balancing selection — what provided tremendous protection during hundreds of years of plague epidemics has turned out to be autoimmune-related now. A hyperactive immune system may have been great in the past but in the environment today it might not be as helpful."
The new study is published in the journal Nature.