The Enduring Mysteries of Plague and Leprosy
Why did plague outbreaks last so long? Was leprosy present in America before the arrival of Europeans? Researchers, sometimes referred to as archaeologists of microbes , have delved into these questions by studying bacteria that date back thousands of years.
The journal Science recently published two studies illuminating the histories of these diseases that have haunted humanity for centuries: the plague, which caused the devastating Black Death at the end of the Middle Ages, and leprosy, often associated with images of severely disfigured individuals.
“The plague bacterium has particular significance in human history, making it crucial to understand how these outbreaks spread,” explains microbiologist Javier Pizarro-Cerda , one of the authors of the first study.
Working at the Institut Pasteur in France, which was involved in both studies, Pizarro-Cerda collaborated with scientists from McMaster University in Canada to explore why each plague outbreak endured through the ages.
Over the past two millennia, the world has experienced three pandemics of plague. The first, known as the Plague of Justinian , significantly influenced the end of Antiquity and the onset of the Middle Ages over a span of 200 years. Nearly a millennium later, the second pandemic began with the Black Death, which claimed nearly half of Europe’s population in the mid-1300s, leading to repeated outbreaks for centuries.
The third pandemic originated in Asia during the mid-19th century and continues to this day, with ongoing cases, particularly in sub-Saharan Africa , including countries like the Democratic Republic of Congo, Madagascar, and Uganda.
Researchers examined samples of Yersinia pestis , the bacterium responsible for bubonic plague, from each of these outbreaks. They noted a common thread: in all three instances, the microbe underwent genetic evolution that gradually diminished its virulence.
One might think that an outbreak would die out as a microbe becomes less dangerous; however, by causing milder infections, the plague bacterium has managed to prolong its existence, allowing for increased opportunities to spread from one individual to another.
– An American Leprosy –
The Pasteur researchers confirmed this theory by infecting groups of rats with certain recent samples: indeed, the disease persisted longer when the bacterium’s virulence was reduced.
This represents a significant advancement in understanding plague outbreaks, even though the current context, with antibiotics effectively combating the disease, differs greatly from centuries past.
“This allows us to comprehensively grasp how pathogens can adapt to different situations,” emphasizes Pizarro-Cerda. “Ultimately, we can better understand what plague is and how to develop measures to defend against it.”
The past also sheds light on the present in the second study, which investigates the history of leprosy over millennia.
The Pasteur teams collaborated with researchers from the University of Colorado to analyze hundreds of samples from archaeological digs across North and South America.
They discovered one of the bacteria involved in leprosy, Mycobacterium lepromatosis . These significant samples dated back 9,000 years, well before the arrival of the first European settlers.
“We demonstrate that a form of leprosy existed in America and spread throughout the continent,” summarizes one of the lead authors, Nicolas Rascovan , a specialist in paleogenomics at the Institut Pasteur. “It wasn’t limited to a small part of the continent; it was indeed widespread.”
However, it’s crucial not to absolve colonization entirely. Europeans did introduce another bacterium, Mycobacterium leprae , which until the 2000s was believed to be solely responsible for leprosy.
This discovery will help guide future research into Mycobacterium lepromatosis, which has remained poorly understood since its identification in 2008. “There is still much diversity among this pathogen to uncover,” notes Rascovan. “And now we know to seek it in America, not elsewhere. This aids in devising strategies to combat pathogens and diseases.”
Published on May 29 at 21:11, AFP