Why did \u00a0plague outbreaks\u00a0 last so long? Was leprosy present in America before the arrival of Europeans? Researchers, sometimes referred to as \u00a0archaeologists of microbes\u00a0, have delved into these questions by studying bacteria that date back thousands of years.<\/p>\n
The journal \u00a0Science\u00a0 recently published two studies illuminating the histories of these diseases that have haunted humanity for centuries: the plague, which caused the devastating \u00a0Black Death\u00a0 at the end of the Middle Ages, and leprosy, often associated with images of severely disfigured individuals.<\/p>\n
\u201cThe plague bacterium has particular significance in human history, making it crucial to understand how these outbreaks spread,\u201d explains microbiologist \u00a0Javier Pizarro-Cerda\u00a0, one of the authors of the first study.<\/p>\n
Working at the \u00a0Institut Pasteur\u00a0 in France, which was involved in both studies, Pizarro-Cerda collaborated with scientists from \u00a0McMaster University\u00a0 in Canada to explore why each plague outbreak endured through the ages.<\/p>\n
Over the past two millennia, the world has experienced three pandemics of plague. The first, known as the \u00a0Plague of Justinian\u00a0, 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.<\/p>\n
The third pandemic originated in Asia during the mid-19th century and continues to this day, with ongoing cases, particularly in \u00a0sub-Saharan Africa\u00a0, including countries like the Democratic Republic of Congo, Madagascar, and Uganda.<\/p>\n
Researchers examined samples of \u00a0Yersinia pestis\u00a0, the bacterium responsible for bubonic plague, from each of these outbreaks. They noted a common thread: in all three instances, the microbe underwent \u00a0genetic evolution\u00a0 that gradually diminished its virulence.<\/p>\n
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.<\/p>\n
– An American Leprosy –<\/strong><\/p>\n The Pasteur researchers confirmed this theory by infecting groups of rats with certain recent samples: indeed, the disease persisted longer when the bacterium\u2019s virulence was reduced.<\/p>\n This represents a significant advancement in understanding plague outbreaks, even though the current context, with \u00a0antibiotics\u00a0 effectively combating the disease, differs greatly from centuries past.<\/p>\n \u201cThis allows us to comprehensively grasp how pathogens can adapt to different situations,\u201d emphasizes Pizarro-Cerda. \u201cUltimately, we can better understand what plague is and how to develop measures to defend against it.\u201d<\/p>\n The past also sheds light on the present in the second study, which investigates the history of \u00a0leprosy\u00a0 over millennia.<\/p>\n The Pasteur teams collaborated with researchers from the \u00a0University of Colorado\u00a0 to analyze hundreds of samples from archaeological digs across North and South America.<\/p>\n They discovered one of the bacteria involved in leprosy, \u00a0Mycobacterium lepromatosis\u00a0. These significant samples dated back 9,000 years, well before the arrival of the first European settlers.<\/p>\n \u201cWe demonstrate that a form of leprosy existed in America and spread throughout the continent,\u201d summarizes one of the lead authors, \u00a0Nicolas Rascovan\u00a0, a specialist in \u00a0paleogenomics\u00a0 at the Institut Pasteur. \u201cIt wasn\u2019t limited to a small part of the continent; it was indeed widespread.\u201d<\/p>\n However, it’s crucial not to absolve colonization entirely. Europeans did introduce another bacterium, \u00a0Mycobacterium leprae\u00a0, which until the 2000s was believed to be solely responsible for leprosy.<\/p>\n This discovery will help guide future research into Mycobacterium lepromatosis, which has remained poorly understood since its identification in 2008. \u201cThere is still much diversity among this pathogen to uncover,\u201d notes Rascovan. \u201cAnd now we know to seek it in America, not elsewhere. This aids in devising strategies to combat pathogens and diseases.\u201d<\/p>\n