<P> The Black Death is thought to have originated in the dry plains of Central Asia, where it then travelled along the Silk Road, reaching Crimea by 1343 . From there, it was most likely carried by Oriental rat fleas living on the black rats that were regular passengers on merchant ships, spreading throughout the Mediterranean and Europe . </P> <P> The Black Death is estimated to have killed 30--60% of Europe's total population . In total, the plague may have reduced the world population from an estimated 450 million down to 350--375 million in the 14th century . It took 200 years for the world population to recover to its previous level . The plague recurred as outbreaks in Europe until the 19th century . </P> <P> The plague disease, caused by Yersinia pestis, is enzootic (commonly present) in populations of fleas carried by ground rodents, including marmots, in various areas including Central Asia, Kurdistan, Western Asia, Northern India and Uganda . Due to climate change in Asia, rodents began to flee the dried out grasslands to more populated areas, spreading the disease . Nestorian graves dating to 1338--1339 near Lake Issyk Kul in Kyrgyzstan have inscriptions referring to plague and are thought by many epidemiologists to mark the outbreak of the epidemic, from which it could easily have spread to China and India . In October 2010, medical geneticists suggested that all three of the great waves of the plague originated in China . In China, the 13th - century Mongol conquest caused a decline in farming and trading . However, economic recovery had been observed at the beginning of the 14th century . In the 1330s, a large number of natural disasters and plagues led to widespread famine, starting in 1331, with a deadly plague arriving soon after . Epidemics that may have included plague killed an estimated 25 million Chinese and other Asians during the 15 years before it reached Constantinople in 1347 . </P> <P> The disease may have travelled along the Silk Road with Mongol armies and traders or it could have come via ship . By the end of 1346, reports of plague had reached the seaports of Europe: "India was depopulated, Tartary, Mesopotamia, Syria, Armenia were covered with dead bodies". </P>

When did the black death start to spread