These Two Mutations Turned Not-so-Deadly Bacteria Into the Plague
By Marissa Fressenden Smithsonian.com
The bacterium that causes the Black Plague, called Yersinia pestis, has been infecting humans ever since it evolved 5,000 to 10,000 years ago. But its ancestor, Y. pseudotuberculosis, only causes an illness similar to scarlet fever. Most people recover from an Y. pseudotuberculosis infection after a few weeks. The Plague, of course, is far more deadly. Now, researchers have pinpointed two mutations that helped Y. pestis make the leap from a passing illness to a killer.
Y. pestis can cause three different types of plague — bubonic, which enters through the skin and causes lymph nodes to swell; pneumonic, which attacks the lungs; and septicemic, which infects the blood. Although all three can be deadly, pneumonic plague is rarer and the most serious form of the disease. Without treatment, the bacteria kills close to 100 percent of those infected, explain researchers Daniel Zimbler and Wyndham Lathem of Northwestern University at The Conversation. Along with their colleagues, these two were searching for how Y. pestis gained the ability to infect lungs.
DNA found in the remains of humans killed by the Black Death and buried in a mass grave in London provided clues. Another group’s analysis of that genetic material showed that the bacteria that killed twenty million people in 1348 to 1350 is very similar to modern strains of Y. pestis.