????它最早起源于中國或蒙古的某個地方，仿佛像一只突然從黃沙中鉆出來的蚱蜢。它沿著絲綢之路，跨過廣闊的歐洲大草原，橫穿安那托利亞半島，最后來到位于黑海之濱的克里米亞。所到之處，死亡如影隨形。

????黑海之濱的卡法港一度是熱那亞商人的貿易前哨地。這場瘟疫爆發后，熱那亞商人們抱頭鼠竄地跳上商船，通過黑海狂奔回馬爾馬拉海，然后進入地中海。但不知不覺地，他們也帶回了瘟疫。死神隨著他們下船登岸，從熱那亞、威尼斯、墨西拿的西西里鎮一直掃蕩到法國的馬賽。隱藏在東方鼠蚤腸胃內的鼠疫桿菌隨同其獵物（黑家鼠）的血液四處傳播，同時也進入每一個被感染的人體內。

????這種病菌有多種癥狀體征，比如淋巴腺腫大、肺炎、敗血癥等等。這三種癥狀都有發病快、痛苦、致死率高的特點，很多病人的腹股溝、腋下、頸部淋巴都會冒出腫瘤。每天都有幾千人死亡。

????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.

????僅僅幾周時間，這種疾病就蔓延到了第勒尼安海的貿易重鎮比薩。不到幾個月，它便橫掃西班牙東部和法德兩國。所到之處，十室九空。來自法國加斯科尼的海船又把它載到了英國南端一個名叫梅爾庫姆里吉斯的小港口，它從這里登陸，殺向人口眾多的英國西部港市布里斯托，一個月后傳播到了倫敦。不久后，整個不列顛群島，加上挪威、丹麥，甚至東到俄羅斯，都成了它的肆虐之所。

????它就是歐洲人談之色變的“黑死病(The Black Death)”。或許更適合的名稱應該是“大死亡(Great Mortality)”。在14世紀中葉大約5年的時間里，這種神秘的瘟疫導致數千萬人喪命，也就是說，死神的鐮刀一舉劃掉了當時整個歐洲四分之一到一半的人口。

????黑死病其實并不是第一起在全球范圍內大規模流行的瘟疫。在此之前約8個世紀，查士丁尼大瘟疫大約導致1億人喪命，這種瘟疫據說也是鼠疫。同時黑死病也不是鼠疫在人類歷史上最后一次肆虐。第三次鼠疫大流行又叫“現代瘟疫”，起源于19世紀60年代的中國，至少導致了1000萬人死亡。

????那么，這些瘟疫究竟是由什么觸發的？奧斯陸大學（University of Oslo）生物學家尼爾斯?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鮮見（見下圖），而且偶發的鼠疫病例直到今年夏天還曾在中國和美國出現，去年12月，馬達加斯加也出現了人感染鼠疫的病例。那么這是否意味著黑死病或許又將卷土重來？如果答案是肯定的，這次它會流傳多廣？

????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?