Plague is caused by

On a drizzly April morning in 2006, a geneticist had the sobering task of helping sort 50 boxes of bones in the Museum of London’s basement into two stacks. One contained the remains of people who died 700 years ago during the Black Death. In the other were bones from survivors of the plague who had been buried a year or more later in the same medieval cemetery near the Tower of London. As Jennifer Klunk, then a graduate student at McMaster University, examined the remains, she wondered what made the two groups different. “Why did some people die during the Black Death and others didn’t?” Klunk, now at Daicel Arbor Biosciences, remembers thinking. Other scholars have been pondering that mystery for centuries. But now, by analyzing DNA from those old bones and others from London and Denmark, Klunk and her colleagues have found an answer: The survivors were much more likely to carry gene variants that boosted their immune response to Yersinia pestis, the flea-borne bacterium that causes the plague. One variant alone appears to have Nature. “We were blown away. … It’s not a small effect,” says Hendrik Poinar, an evolutionary geneticist at McMaster and co–lead author of the study (and Klunk’s Ph.D. adviser). The findings also indicate the Black Death caused a dramatic jump in the proportion of people carrying the protective variant; it is the strongest surge of natural selection on the human genome documented so far. But the improved immunity came at a cost: Today, the variant...

Plague is an illness you get from Yersinia pestis bacterium. You usually get the most common form (bubonic plague) from flea bites, but you can get pneumonic plague from someone who’s infected. Plague caused deadly pandemics in the past and still exists in many countries today. You can survive plague if you’re treated with antibiotics quickly. Overview You usually get bubonic plague from flea bites. It can move into your blood and cause septicemic plague. Pneumonic plague is uncommon but can spread from person to person. What is plague? Plague is an illness you get from the bacterium Yersinia pestis (Y. pestis). Plague is a zoonotic disease, which means you can get it from animals and they can get it from you. This disease usually spreads through bites from fleas that previously bit an infected animal. There are three types of plague. Which type you have depends on where in your body Y. pestis ends up. Bubonic plague infects your lymph nodes, septicemic plague is in your blood and pneumonic plague affects your lungs. What is the plague called today? Today we still use the word “plague” to mean illness caused by Yersinia pestis. Usually, we also call it by the specific type of plague it is — bubonic, septicemic or pneumonic. Does plague still exist? Yes, plague still exists. It’s most common in parts of Africa, but a few cases are reported in Asia, South America and the U.S. every year. What are the three plagues? The three types of plague — bubonic, septicemic and pneumoni...

Rats have long been blamed for spreading the However, a new study suggests that rats weren’t the main carriers of fleas and lice that spread the plague—it was humans. In Proceedings of the National Academy of Sciences, researchers simulated Black Death outbreaks in European cities to try and understand how the plague was spread. In their simulations, they looked at three possible models for infection: rats, airborne transmission, and fleas and ticks that humans carry around with them on their bodies and clothes. A flea infected with the plague. (Credit: Smith Collection/Gado/Getty Images) In most of the cities, the model that focused on fleas and ticks on humans was the most accurate model for explaining the spread of the disease.Though it may come as a surprise to most readers, “It would be unlikely to spread as fast as it did if it was transmitted by rats,” Nils Stenseth, a professor at the University of Oslo and co-author of Monday’s study, It’s not clear where the belief that rats spread the plague came from in the first place. After all, the researchers write that “there is little historical and archaeological support for such a claim.” For example, if rats really were a main cause of the plague, there would be more archaeological evidence of dead rats.