The black rat, Rattus rattus. Source Wikipedia

Contrary to many people’s understanding, the plague is not a thing of the past. Although it disappeared from Europe in the early 1900s it still persists in many pockets around the world (see map), as witnessed by the currentoutbreak in Madagascar。Analysis of DNA and immunoprotein samples from the remains of medieval plague victims has confirmed that the Black Death and subsequent plague epidemics were caused by the same bacterium,Yersinia pestis，，，，作为现代爆发。

亚历山大·耶尔辛（Alexandre Yersin）发现了造成欧洲瘟疫大流行的杆菌的发现后不久，公认的医学理解是，瘟疫是从侵扰黑色大鼠的人类传播给人类的。感染的跳蚤因此充当载体。当大鼠开始大量死亡这种疾病时，感染了跳蚤的替代宿主，因此被感染了。

However the role of the black rat has been challenged by several investigators. For example,安妮·卡林·霍夫纳默（Anne Karin Hufthammer）反对黑人大鼠参与斯堪的纳维亚宫瘟疫流行病的案例。她的挑战基于骨骼组合的考古信息，这些信息表明，尽管瘟疫爆发了常规爆发，但在挪威，黑鼠在中世纪很少见。确实，在此期间，欧洲整个欧洲的寒冷气候条件可能不利于黑大鼠的种群生存或东方大鼠跳蚤的生存，Xenopsylla cheopsis在欧洲大部分地区。The now common brown rat had not arrived in Europe at this time.

One of the places where the plague bacterium persists is in the Central Asian Deserts, where the great gerbil,Rhombomys opimus，，，，is the primary host. Gerbils are social animals, living in burrows infested with several parasitic arthropods, including the fleas that act as vectors for the bacterium. Gerbil populations fluctuate and the sylvatic plague bacterium will spread in the population when it exceeds an upper threshold level.Work published in 2007 by Nils Christian Stenseth正在研究哈萨克斯坦的沙鼠种群的同事们，建议在气候条件，植被覆盖率，沙鼠密度和瘟疫传播的同步增加之间存在共同依赖性。温暖，潮湿的条件可促进这些干旱地区的植被生长，从而产生大量的沙鼠种群和大鼠疫。随着沙鼠种群崩溃，跳蚤种群的增加，瘟疫细菌散布并感染了跳蚤溢出到家畜和人类上。

该小组的最新研究有just been published。Here they asked whether climatic fluctuations were also responsible for the waves of plague pandemics that swept Europe after the initial Black Death of 1347-1353.

当然，13 /14世纪没有可靠的气候记录，因此Stenseth和他的同事在寻找中世纪欧洲的气候波动与瘟疫爆发之间的关系时，将基于树环的数据作为气候代理。

他们使用了在黑死亡后发生的7,711次瘟疫爆发的历史记录以及对欧洲和亚洲占据的15种基于树环的气候代理的数据进行的数据。与现代亚洲爆发不同，在瘟疫爆发和气候状况之间找不到任何关联。

Furthermore, there was little evidence that there was a local wildlife reservoir ofY. pestis那本来可以发起新的爆发。为了确定这一点，他们选择了在采集了一个树环样品的位置500公里以内发生的疫情，在1000公里的半径内，过去两年中没有瘟疫爆发的地方。是新爆发的来源。该分析表明，大多数暴发可能归因于附近的先前爆发，因为只有24集只能由当地啮齿动物种群中细菌储层引发。此外，历史上有8个已记录在瘟疫感染地区的运输中引入了其中的8个。

These findings caused then to turn their attention to the possibility that each new wave of disease had a maritime origin.

Using the same criteria to select locations, they were able to detect 61 potential maritime introductions that occurred between 1346 and 1856 in 17 harbours around the Mediterranean and the Black Sea coasts. These sea routes linked Europe with the overland routes to Asia. Historical reports were used to identify 16 potential introductions from Asia. Periods of climatic fluctuations were identified from tree ring analysis at sites on these ancient trade routes to Central Asia. Here populations of long tailed ground squirrels and Altai marmots are the rodent reservoir of plague.

他们发现一段约15年consistently occurred between a climatic fluctuation in the Karakorum mountain range in northern Pakistan and a plague reintroduction in Europe. This suggest a scenario whereby; 1-2 years after a climatic fluctuation, the rodent populations crashed and infected fleas sought alternative hosts. A period of 10-12 years followed when, they hypothesised, the disease travelled West via caravan routes to the sea (the ancient Silk Road). It took a further 2-3 years to spread into Europe via maritime trade routes.

Evidence for the spread via the ancient caravan routes requires further investigation but camels are easily infected with plague from the bites of fleas and the bacillus could also have travelled in infected traders, other animals or fleas in their cargo.

看来，我们可能需要重写历史书籍，并将这些古老的祸害归咎于欧洲的面貌，而不是谦卑的老鼠。