Plague is a severe infectious disease caused by Yersinia pestis infection. It is an international quarantine infectious disease and a Class A infectious disease among the legal infectious diseases in China, ranking first among 39 legal infectious diseases. Plague is a natural infectious disease, which is mainly prevalent among rodents. Rats and marmots are natural hosts of Yersinia pestis. Rat fleas are vectors of transmission.

The clinical manifestations are severe toxic blood symptoms such as high fever, swollen lymph nodes, cough, expectoration, dyspnea and bleeding. This disease is highly contagious and has a high mortality rate. There have been many pandemics of plague in the history of the world, and there were also many pandemics before the liberation of China. At present, it has been greatly reduced, but there are still sporadic cases in western and northwest China.

The Black Death entered Europe in 12- 13 century, which had a great impact on the historical development of Europe.

1, the Black Death caused a large population decline. Many cities have a mortality rate of over 40%, and some small towns are almost dead.

The population pressure in Europe has been greatly reduced.

2. The Black Death led to the massive evacuation of urban population and accelerated the disintegration of feudalism in European city-states. At the same time, the death of a large number of monks also led to the weakening of the church's control over religious forces.

The Black Death became the beginning of the Renaissance. Decameron and other representative works of the Renaissance were born in the period when the Black Death raged.