Latest news with #JustinianPlague
News18
05-06-2025
- Health
- News18
What Is Yersinia Pestis, The Plague Bacteria That Has Infected Humans For 5,000 Years?
Last Updated: Though most associate plague with a singular moment in medieval Europe, researchers say the bacteria has been infecting humans for at least 5,000 years The plague that once wiped out millions in Europe hasn't truly vanished, and now scientists are beginning to understand why. A new study published in the journal Science reveals how the deadly bacterium behind the infamous Black Death, Yersinia pestis, evolved over centuries to become less lethal but more persistent, allowing it to survive, spread, and silently persist in the background of human and animal populations for millennia. Though most associate plague with a singular moment in medieval Europe, researchers say the bacteria has been infecting humans for at least 5,000 years, flaring up in three major pandemics, i.e. the Justinian Plague in the 6th century, the Black Death in the 14th century, and a third outbreak that began in 19th-century China. The Black Death alone is estimated to have killed between 30% and 50% of Europe's population in just five years, roughly 25 million people. The answer, scientists believe, lies in its ability to adapt, specifically through changes in a single gene called pla, which produces an enzyme that allows the bacteria to spread through the body by breaking down blood clots. At the height of the Black Death, Yersinia pestis strains were highly lethal, killing victims within days. But as the outbreak continued, researchers have found that the bacteria began to evolve. Mutations in the pla gene led to the emergence of less aggressive strains, ones that killed more slowly, giving the infection more time to move from host to host before the host died. When scientists compared ancient DNA from plague victims with more recent samples, they discovered that the older, weaker strains had fewer copies of the pla gene. Mice infected with this variant took two days longer to die and showed a 10-20% lower mortality rate. That's a small biological shift, but one with enormous implications. By becoming less deadly, the plague became more dangerous in a different way; it spread farther, infected more people, and embedded itself more deeply in human and animal ecosystems. The Plague Hasn't Disappeared While modern medicine has made plague treatable with antibiotics, the disease hasn't been eradicated. Today, it still appears sporadically in remote areas of Asia, Africa, the Americas, and even the western United States. Rodents like prairie dogs and ground squirrels continue to harbour the bacterium, and over 300 rodent species are capable of carrying and spreading it. Dr Deborah Anderson, a researcher involved in the study, said her team is now focusing on how Yersinia pestis cycles between fleas and rodents, especially how changes in the pla gene could determine how outbreaks emerge or fizzle out in animal populations. One of the study's more striking findings relates to how epidemics behave over time. Using mathematical models, scientists observed that during the early phases of an outbreak, both humans and rats die rapidly. But when rodent hosts start dying in large numbers, the bacteria 'learns" to moderate its aggression. In evolutionary terms, a dead host is a dead end, so the plague weakens just enough to keep its hosts alive a little longer, giving itself a better chance to jump to a new one. This self-limiting behaviour can lead to an 'epidemic burnout," where the disease appears to die out, but actually persists, lying dormant in new hosts or new environments. That's likely why weaker strains of the bacterium, with muted pla activity, are still being discovered in modern samples, including a human and two black rats in Vietnam. Lessons from the Plague The tale of the plague isn't just a relic of medieval history. Scientists say it offers valuable lessons for understanding modern pandemics, including Covid-19. Like the plague, the coronavirus has evolved into forms that are less fatal but more transmissible, allowing it to quietly circulate in populations worldwide. The key difference is that we now have the tools to track these changes in real time. What makes Yersinia pestis so scientifically important is the sheer amount of historical genetic data available, spanning thousands of years, an unrivaled resource in the study of infectious disease. In a world where new pathogens can emerge and mutate rapidly, the ancient plague may hold the keys to anticipating what comes next. Location : New Delhi, India, India First Published: June 05, 2025, 13:57 IST News world What Is Yersinia Pestis, The Plague Bacteria That Has Infected Humans For 5,000 Years?
Yahoo
30-05-2025
- General
- Yahoo
Single gene may help explain the plague's persistence throughout human history
When you buy through links on our articles, Future and its syndication partners may earn a commission. Scientists have discovered how adaptations in a single gene helped the plague survive for hundreds of years. Responsible for the deadliest pandemic in history, the bacterium that causes the plague, Yersinia pestis, has existed in varying strains from ancient times until today. Now, scientists have unearthed a genetic clue as to how the infamous disease has persisted for millennia, with devastating outbreaks smoldering across centuries. They published their findings Thursday (May 29) in the journal Science. "This is one of the first research studies to directly examine changes in an ancient pathogen, one we still see today, in an attempt to understand what drives the virulence [disease severity], persistence and/or eventual extinction of pandemics," study co-senior author Hendrik Poinar, director of the Ancient DNA Centre at McMaster University in Ontario, Canada, said in a statement. Y. pestis has been infecting humans since before recorded history began. The most common form of the disease is known as "bubonic" and most often enters the body through bites from infected fleas, although people can less commonly catch it directly from infected animals, including rats and cats. Once inside the body, the bacterium travels to the lymph nodes and replicates. As it multiplies, it triggers the formation of painful, pus-filled "buboes," for which the bubonic plague is named. The plague bacterium can also cause a blood infection, called septicemic plague, and lung infection called pneumonic plague. Related: Oregon's 1st bubonic plague case in 8 years tied to patient's pet cat The three major plague pandemics are among the deadliest outbreaks in human history. The first pandemic, the Justinian Plague (which occurred roughly between A.D. 542 and 750), slashed the population in parts of the Mediterranean to by an estimated 40% by the end of the sixth century. The second, and most infamous, outbreak of the disease was the 14th-century Black Death that ravaged Europe and the Middle East. The single deadliest pandemic in recorded history, the Black Death killed approximately 25 million people in Europe alone — between 33% and 50% of its population. A third, lesser-known global plague pandemic began in 1855 in China's Yunnan province and killed more than 12 million people in India and China alone. This pandemic was considered active until 1960, after which plague deaths dropped to lower levels. Plague epidemics continue to this day, with the Democratic Republic of the Congo, Madagascar and Peru being the most endemic countries, according to the World Health Organization. Besides the staggering death counts associated with the pathogen, what's perhaps most remarkable about Y. pestis is the longevity of its strains. Strains of the Justinian Plague bacterium took 300 years to go extinct after outbreaks were first recorded, and one of the two lineages from the Black Death re-emerged in waves for 500 years before its disappearance, while the other became the ancestor of all present-day strains. To investigate the genetic toolkit Y. pestis uses to persist for so long, researchers conducted an analysis of a plague gene known as pla across hundreds of samples collected from ancient and modern victims of the disease. The pla gene codes for an enzyme that helps Y. pestis move through the body undetected by the host's immune system. Previous studies have suggested that pla is a key factor that modulates both the lethality of a given plague strain and its ability to spark outbreaks in humans. However, one plague strain can carry a different number of pla genes than the next, and it wasn't clear how this copy number might impact their biology, the researchers noted. To investigate, they collected multiple modern strains of Y. pestis from Vietnam that had varying numbers of copies of pla inside their genomes; carrying more copies of the gene means that the bacteria can crank out more copies of the enzyme. After injecting these different plague strains into mice, they found that the strains with fewer copies of pla led to longer infections but reduced the disease's mortality rate by up to 20%. RELATED STORIES —Diagnostic dilemma: A scientist caught plague from bacteria thought to be 'noninfectious' —Could bacteria or viruses lurking in ancient Egyptian mummies unleash a plague today? —'Black death' survivors had plague-resistant genes that may boost their descendants' risk of autoimmune disease Across the ancient plague genomes they analyzed — 20 of which dated to the first plague pandemic and 94 of which were from the second — the researchers noted a pattern where the plague strains lost copies of pla over time, namely in later stages of each pandemic. Among the modern genomes, they found three strains that hint that the same pattern is unfolding today. They theorized this adaptation likely made infections less virulent, or harmful to the host's body, over time. This suggests that the evolutionary change helped the disease to keep its hosts — be they rat or human — alive for longer, thereby enabling it to spread more widely. This adaptation may have been especially necessary after populations of the plague's primary hosts, rats, were killed off en masse during outbreaks. "The reduction of pla may reflect the changing size and density of rodent and human populations," Poinar said. "It's important to remember that plague was an epidemic of [flea-ridden] rats, which were the drivers of epidemics and pandemics. Humans were accidental victims." The scientists say that further research into both ancient and contemporary plague strains could reveal more pla depletions and help them to better understand how such changes to the germ's genome have shaped its virulence through history. Nowadays, Y. pestis infections can be cured with antibiotics, though some strains have shown troubling signs of antibiotic resistance. To head off the threat of a superbug plague outbreak, scientists in the U.K. have already started developing a bubonic plague vaccine to add to stockpiles. This article is for informational purposes only and is not meant to offer medical advice.
