The Lingering Legacy of the Bubonic Plague: How the Disease Continues to Impact Humanity
Bubonic plague, a disease that once caused mass devastation and wiped out a third of Europe’s population, may still have a lasting impact on humankind. While modern antibiotics have made it easier to treat, the disease can still be found in scattered locations around the world. The mention of the bubonic plague evokes both fear and fascination, as it remains a rare but intriguing disease.
In the US and Europe, the bubonic plague is now vanishingly rare, thanks to changes in lifestyles that prevent its spread from infected fleas to humans. However, cases still occur, such as the recent incident where a man in Oregon contracted the disease from his pet cat. According to evolutionary geneticist Paul Norman from the University of Colorado, Anschutz, there are still small pockets of plague in the US, circulating among wild animals like squirrels and prairie dogs. On average, around seven cases of plague in humans are reported in the US each year, with deaths being less common. In places like Madagascar, the disease is more prevalent.
The bubonic plague has left its mark on humanity and can still be found in the genomes of people living today. Yersinia pestis, the bacterium responsible for the disease, is believed to have plagued humans for thousands of years. DNA evidence of the bacteria has been discovered in skeletons dating back 4,000 years. However, it was in the early 1300s that a strain of the bacteria known as the Black Death spread across Europe, causing millions of deaths. It is thought to have originated in villages around what is now Kyrgyzstan, possibly passing through fleas from infected marmots into humans before spreading along the Silk Road trade route to Europe.
The Black Death is estimated to have killed about 50 million Europeans by the mid-1300s. Recent research suggests that the toll may not have been as dramatic everywhere, with some regions being devastated while others were barely affected. Nonetheless, plague is believed to have claimed at least 200 million lives over the centuries. Due to the catastrophic nature of plague outbreaks, researchers have long wondered if they left a permanent imprint on the human immune system. One theory proposes that the Black Death could have created a form of natural selection, favoring individuals who possessed genetic traits that helped them survive the disease.
Gathering data to answer this question has been challenging until recently. Sequencing DNA from ancient plague victims’ skeletons found in mass burial sites is notoriously difficult due to contamination and degraded DNA. However, scientists have found intact human DNA in a tiny bone called the bony labyrinth, located within the inner ear. This dense bone has proven to be a reliable source of DNA. By studying this DNA, researchers have gained new insights into who survived past plague outbreaks and why.
A recent study led by Paul Norman investigated a mass grave of plague victims from the 16th Century in the German town of Ellwangen. The researchers sequenced genomes from 36 skeletons and compared them with the DNA of present-day inhabitants of Ellwangen. They found subtle differences in various genes related to the human leukocyte antigen (HLA) system, which plays a crucial role in coordinating the immune response. These genetic differences likely rendered their ancestors more capable of fighting off Yersinia pestis.
Another study examined genetic samples from around 500 people who died before, during, and after the 14th-Century Black Death in London and Denmark. The researchers identified patterns related to a gene called ERAP2, which encodes a protein that helps human immune cells combat Yersinia pestis and other pathogens. They discovered that individuals carrying a specific variant of ERAP2 were twice as likely to have survived the Black Death. By the end of the 14th Century, this variant was present in 50% of Londoners and 70% of Danes surveyed.
However, more research is needed to fully understand the impact of the Black Death on human immunity. Scientists must study thousands more genomes from individuals living across Europe during the time of the Black Death and subsequent centuries. This will help determine if genetic adaptations, such as the ERAP2 variant, became widespread and integrated into our DNA.
While diseases like smallpox may have had a greater impact on shaping modern immune systems, the bubonic plague remains a subject of fascination. Studying how it affected our ancestors provides valuable information for understanding the evolution of strains and developing vaccines and drugs today. By examining ancient DNA, scientists can learn how evolution dealt with diseases thousands of years ago and apply those lessons to current medical advancements.
The legacy of the bubonic plague continues to linger, reminding us of the devastating impact it had on humanity. Although rare, the disease still poses a threat in certain parts of the world. By unraveling its genetic secrets, researchers hope to gain a deeper understanding of our immune system’s response to
