It had started somewhere in China, or Mongolia perhaps, emerging like an ancient locust from the soil. Shadowing the Silk Road, it had crossed the vast Eurasian steppe, traversed the Anatolian peninsula, and arrived in Crimea on the Black Sea. Everywhere, death had followed.
At the Black Sea port of Caffa, where merchants from the Italian city of Genoa had set up a trading outpost, the pestilence landed with a fury. The Genoese fled to their ships, racing back through the Black Sea, to the Sea of Marmara, then to the Mediterranean. Unknowingly, they brought the sickness and fury with them. From ship to port—Genoa, Venice, the Sicilian town of Messina, the French harbor of Marseille—the microscopic Yersinia pestis followed, hiding in the stomachs of Oriental rat fleas, circulating in the blood of their prey, the black rat, and within each new human being infected.
The illness came in various forms—bubonic, pneumonic, septicemic. All three were swift, painful and gruesome, with many of the victims developing oozing tumors in their groins, armpits, or necks.
它就是欧洲人谈之色变的“黑死病(The Black Death)”。或许更适合的名称应该是“大死亡(Great Mortality)”。在14世纪中叶大约5年的时间里，这种神秘的瘟疫导致数千万人丧命，也就是说，死神的镰刀一举划掉了当时整个欧洲四分之一到一半的人口。
那么，这些瘟疫究竟是由什么触发的？奥斯陆大学（University of Oslo）生物学家尼尔斯•克里斯蒂安•斯坦瑟斯及其同事指出，鼠疫病菌的宿主生物在全球各地都不鲜见（见下图），而且偶发的鼠疫病例直到今年夏天还曾在中国和美国出现，去年12月，马达加斯加也出现了人感染鼠疫的病例。那么这是否意味着黑死病或许又将卷土重来？如果答案是肯定的，这次它会流传多广？
It took only weeks for the disease to arrive in Pisa, a center of trade on the Tyrrhenian Sea. It took mere months to carve through Eastern Spain, France and Germany, slicing through the population as if clear-cutting a forest. Ships from Gascony in Southwestern France hauled the disease to Melcombe Regis, a small seaport on England’s southern flank. From there, it was carried to crowded Bristol, a month later to London, and before long to all the British Isles, Norway, Denmark, as far east as Russia.
“The Black Death,” it was called; yet even more fitting was the name, the “Great Mortality”: Over the course of some five years in the mid-14th century, the mysterious plague claimed the lives of tens of millions of people—a reign of terror that, by most assessments, killed between a quarter and half the population of Europe.
This wasn’t the first time a massive, globe-spanning pandemic had taken hold: Eight centuries earlier, the Justinian plague—ostensibly caused by the same microbe—had killed an estimated 100 million people. Nor would it be the last devastating outbreak of Y. pestis. A third major pandemic, the so-called Modern Plague, began in China in the 1860s and claimed at least 10 million lives before it was through.
What triggered any of them? University of Oslo biologist Nils Christian Stenseth and colleagues have shown that reservoirs of the plague bacteria remain common in much of the world (see map below). And sporadic cases of bubonic plague have popped up as recently as this summer in the U.S., and in China, as they did in Madagascar in December. Could another Black Death take hold and, if so, how far would it spread?