Yersinia+pestis

//Yersinia pestis// is the bacterium that caused the Black Death, both the famous medieval ones in Western Europe (peaking in 1348-1350) and the Plague of Justinian. It was thought to have originated in Central Asia, possibly around the Gobi Desert. It was carried to Europe along the Silk Road and by Mongol armies at the peak of their westward expansion. It was carried by fleas which infested the common black rat, and was transmitted in its bubonic form by these same fleas and by tactile contact, and in its pneumonic form through the air. It killed off about half the population of Europe, with higher mortality rates in the warmer Mediterranean countries. It is notable for its impact on the economy and social hierachy: because of a labor shortage, the lower classes were able to secure more rights and better treatment at the hands of the nobility; this is concurrent with the rise of towns and the bourgeoisie.