Carlos Rojas in The Naked Gaze:
In an intriguing hypothesis sketched out in Plagues and Peoples (1976), William McNeill speculates that Europe’s 14th century Black Death plague may have had its origins in the Eurasian Steppes, where the virus may have been endemic among the region’s burrowing rodents for centuries before finally being transmitted to China, then the middle East and Europe by horse-riding Mongols as they established the Mongol Empire (1206-1368).
Although many scholars (including Graham Twigg, Susan Scott, and Christopher Duncan) now question whether the Black Death was actually a case of bubonic plague, or any bacterial disease, or was even necessarily any single disease at all, it is nevertheless acknowledged that the last world-wide pandemic of bubonic plague (known as the “third pandemic”) did in fact have its origins in central China before eventually spreading to Hong Kong in 1894, and then (like the SARS outbreak threatened to do a century later) on to trading ports around the world. While the worst of the 1894 Hong Kong epidemic was controlled relatively quickly, the global pandemic which it precipitated dragged on for decades, and was not officially conquered (according to the WHO) until 1959.
More here.