Scientists working in China have recently linked climate conditions with outbreaks of the plague bacteria, Yersinia pestis. Plague bacteria is primarily spread by fleas that reside on rodents. During warm, wet months there is more vegetation growth which means an abundance food for rodents. More rodents means more fleas, hence greater spread of plague.
Yersinia pestis is the leading culprit in the Black Death, an epidemic that swept through Europe in the 14th century and ultimately killed 1/3 of the world’s population. The Black Death originated in China and made its way to Europe via traders – most famously when a ship filled with dead or dying men stricken by the plague landed in a Sicilian port in 1347. From there, the plague spread exponentially leaving a swath of death in its wake.
While the plague bacteria still exists today, it is largely controlled and treatable (if detected early). Additionally, better sanitation conditions help to keep the disease at bay. To read more about the new scientific determinations about the connection between weather conditions and the plague, read this article by Discovery News. If you would like to read more about the Chinese origins of the Bubonic Plague, read this article by Discovery News.