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The Black Death, the 14th-century bubonic plague that killed some 1 in 3 people in Europe and an estimated 200 million across the world, has left another long-lasting mark: on the immune systems of people living today.
Four DNA variants appear to have helped boost survival rates from the plague — caused by a bacterium, “Yersinia pestis,” carried by small mammals and their fleas — in the mid-1300s and in recurring bouts of plague in later centuries, according to a recent study published in the journal Nature.
Researchers from the University of Chicago, McMaster University in Ontario and the Pasteur Institute in Paris say 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.
Hendrik Poinar, a professor of anthropology at McMaster University and senior co-author on the study, said in the release that the research offered insight into “how pandemics can modify our genomes but go undetected in modern populations.”
Poinar noted that while the genes “provided tremendous protection during hundreds of years of plague epidemics,” they are linked to autoimmune disorders. “A hyperactive immune system may have been great in the past but in the environment today it might not be as helpful,” he said.
Having “two copies of a specific variant of one gene in particular, ERAP2, was strongly associated with surviving the plague,” according to a video published by the University of Chicago to explain the findings. People who survived the Black Death eventually passed the genetic variant to their children. Individuals who inherited such mutations were about 40 percent more likely to survive the plague, the research found.
Luis Barreiro, a professor of genetic medicine at the University of Chicago, said in a release on the study that the group’s findings served as “evidence that this one single disease event was enough to lead to selection in the human immune system.”
Barreiro said the findings were one of a kind. “This is, to my knowledge, the first demonstration that indeed, the Black Death was an important selective pressure to the evolution of the human immune system,” he said.
The medieval plague remains a topic of fascination among researchers and historians due to its “extensive demographic impact and long-lasting consequences,” the study notes, some 700 years after the deadliest pandemic recorded in history.
Researchers involved in the study analyzed high-quality genetic variation in more than 200 DNA samples extracted from the bones or teeth of individuals from Denmark and London who lived before the plague, died of it or lived between one and two generations after it swept the world.
There are different clinical forms of plague, though the most common are bubonic, pneumonic and septicemic, according to the Centers for Disease Control and Prevention. The Black Death, also referred to as the Pestilence, was a bubonic plague pandemic. Symptoms included skin tissue darkened by gangrene and swelling of lymph nodes, or buboes — the source of the term “bubonic.”
DNA evidence reveals where the Black Death began
The plague strain eventually evolved into a less-dangerous variety, and today the protective variant is present in about 45 percent of British people, according to the 1000 Genomes database, Science Magazine reported in a write-up of the study. Deadly plague outbreaks remain a threat in some areas, but prevention and treatment methods have improved drastically, especially through the use of antibiotics.
Bubonic plague was so deadly an English village quarantined itself to save others
The findings have raised the question: Will the coronavirus pandemic have a big impact on human evolution?
Fortune magazine reported that Barreiro is not convinced. The Black Death was far deadlier, he said, killing on scale orders of magnitude beyond the effects of covid-19, and had a more devastating effect on the young, killing people before they could pass on their genes.