How Black Death survivors gave their descendants an edge during pandemics

Using DNA extracted from teeth of people who died during and after the Black Death pandemic, researchers were able to identify genetic differences between those who survived and who died from the virus./Matt Clarke/McMaster University

The bubonic plague ravaged London when it reached there in 1348. The cemeteries in the city were overflowing since so many people died suddenly.
“So the king [Edward III], at the time, bought this piece of land and started digging it,” says geneticist Luis Barreiro at the University of Chicago. This cemetery, called East Smithfield, became a mass grave, where more than 700 people were buried together. “There’s basically layers and layers of bodies one on top of each other,” he says. The city shut down the cemetery when the outbreak ended.
In the end, the so-called Black Death, a bubonic plague, probably claimed the lives of 30 to 50 percent of people in certain regions of Europe and the United Kingdom. According to Barreiro, that death rate is at least 200 times higher than the COVID estimate.
“We all think that COVID-19 was insane and completely changed the world and our societies,” Barreiro says. “COVID has a mortality rate of about 0.05% – something like that. Now try to project – if it’s even possible – a scenario where 30 to 50% of the population dies.”
A recent study that was released on Wednesday in the journal Nature demonstrates that the Black Death likely affected the genetic evolution of the European people in addition to society.
In the research, Barreiro and his colleagues discovered that Black Death survivors in London and Denmark had a genetic advantage thanks to changes that let them resist the Yersinia pestis, the virus that causes the plague. Many Europeans still retain those mutations today because survivors passed them on to their offspring.

RELATED: Scientists say they’ve solved a 700-year-old mystery: Where and when Black Death began

A woodcut from the 15th century depicts a scene from the Black Death plague, which killed an estimated 50 million people in Europe and the Mediterranean between 1346 and 1353. Scientists say they may have found the origin of this deadly disease.

But that edge comes at a cost: It increases a person’s risk of autoimmune diseases. “The exact same genetic variant that we find to be protective against Yersinia pestis is associated with an increased risk for Crohn’s disease today,” Barreiro says.
The study demonstrates how past pandemics could prepare the human immune system to survive future pandemics.
“The evolution is faster and stronger than anything we’ve seen before in the human genome,” says evolutionary biologist David Enard at the University of Arizona, who wasn’t involved in the study. “It’s really a big deal. It shows what’s possible [for humans], in terms of adaptation in response to many different pathogens.”
Did the Londoners who survived the Black Death have a mutation, or even mutations, in their genomes that protected them from the disease? was the straightforward question Barreiro and his team set out to address in the study.
They had to harvest DNA from people who perished in the epidemic 700 years ago, which is something that almost sounds like sorcery, in order to get the answer to that question.
The significance of the East Smithfield cemetery arises in this context. Because this cemetery was only utilized by London officials during the years of around 1348 and 1349 due to the Black Death, scientists can precisely determine the age of the remains buried there. Additionally, Barreiro and his team were able to examine the DNA of persons who passed away before the Black Death, during it, and after it.

RELATED: How A Medieval City Dealing With The Black Death Invented Quarantine

For nearly three centuries, the Republic of Ragusa, where modern-day Dubrovnik is centered, forced visitors to spend 40 days on the remote islands off the coast of the walled city, but in the 17th century, the city built the Lazarettos, a series of buildings immediately outside the city where visitors had to quarantine. This is the view from one of the quarantine cells./ Rob Schmitz/NPR

Then they looked specifically at genes involved with the immune system to see if any mutations correlated with survival during the plague. The team also ran a similar experiment with DNA extracted from people buried in Denmark.
When they combined the two experiments, the researchers hit the jackpot.

Researchers extracted DNA from the remains of people buried in the East Smithfield plague pits, which were used for mass burials in 1348 and 1349. / Museum of London Archaeology (MOLA)

Not only one, but four mutations were discovered, which most likely provided an edge to Londoners during the Black Death. Additionally, the benefit was considerable. One mutation in the ERAP2 gene provided people a 40% increase in their chance of surviving the plague.
According to Enard, that is the greatest evolutionary benefit yet observed in humans. And over a few decades, he claims, the advantage developed incredibly quickly.
According to Enard, until this study, the development of lactose tolerance in Europeans was the best illustration of natural selection in humans. Although it had developed over thousands of years, it still only provided a little survival advantage.
An important part of the immune response is launched early in an infection thanks to the ERAP2 gene. Barreiro and his team discovered that individuals with a mutation in the ERAP2 are likely capable of killing invasive germs more quickly than individuals without this mutation. The mutation probably intensifies an inflammatory response that aids in infection eradication.
However, according to paleogeneticist Maria Avila Arcos of the National Autonomous University of Mexico, excessive inflammation might cause problems. “That’s kind of the balance,” she said. “If your immune system is very robust, then that might lead to autoimmune illnesses.”
In fact, ERAP2 is one of many mutations that currently raise the risk of autoimmune disorders like rheumatoid arthritis in addition to protecting against the Black Death.
The current study, according to Avila Arcos, has a significant flaw: It mainly concentrates on a very small demographic, primarily those who were living in Denmark and London at the time. However, the Black Death affected a wide range of populations in Europe, Asia, and North Africa. According to her, “humans may have deployed a lot more cellular systems to combat this deadly disease.” But all we’re observing are similar mechanisms between English and Danish.

RELATED: Why Pandemics Give Birth To Hate: From Bubonic Plague To COVID-19

The pandemic has been responsible for an outbreak of violence and hate directed against Asians around the world, blaming them for the spread of COVID-19. During this surge in attacks, the perpetrators have made their motives clear, taunting their victims with declarations like, “You have the Chinese Virus, go back to China!” and assaulting them and spitting on them.

According to medical historian Monica H. Green, who has spent 15 years researching the Black Death, the study’s findings could easily be misunderstood by the general public to support racist stereotypes about European immunity.
“There’s a general idea, found in a lot of these popularizing essays, books and so forth, that Europeans are immunologically superior to every other population on the planet precisely because Europe has had this long history of exposure to all these diseases, like the Black Death,” she explains. “Basically, if Europeans survived, that automatically means that they’re the superior race.
She’s concerned the findings of this new study will reinforce this idea because there’s no data on other populations, such as people in Asia or northern Africa.
“If there’s not comparable genetic work on these populations,” she says, “then the racists are going to come along and interpret these new findings in any way that they want.”


by: Miss Cherry May Timbol – Independent Reporter
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