The most infamous plague of all time was the black death. Between 1347 and 1351, the black death swept through Europe killing 1 in of every 3 people. Black death originated in China and Inner Asia before being passed onto Europe when the Kipchak Army catapulted corpses that had been infected with the plague during a fight. A rough estimate of 25 million people died and about 1,000 villages had disappeared.
Recently, researchers have discovered how just a small amount of genetic changes can mutate a small stomach bug into a large pandemic. The bacteria responsible for creating this plague is Yersinia pestis. A gene named pla gave this bacteria the power to cause pneumonia. This kills everyone that is not able to get antibiotics. A 20-million-year-old flea found incapsulated in amber could possibly be an ancestor to this Y.pestis bacteria.
Researchers decided to research this bacteria with an ancestor of it called Y. pseudotuberculosis. They cut Y. pseudotuberculosis and fed it to many different fleas. Only the fleas who ate the protective coating of the bacterium became ill. The protein found in the coating is called urease. Taking this protein and put it into Y.pestis and the fleas yet again became sick, when before they did not.
There are so many other things that are not known yet about the bacteria, but researchers are delving into this and trying to figure out what it does. Maybe plagues could be avoided at some point, but we may never know.