An early historical example are the rats that crusaders brought back from the Middle East as spoils of victory in the fourteenth century. These rats and the fleas on them were the cause of the plague that decimated more than a fourth of Europe.
歷史早有教訓，十四世紀十字軍東征無意中由東方帶回的「戰利品」之一﹘ ﹘老鼠和它身上的跳蚤，將腺鼠疫傳到人類身上，造成歐洲人口四分之一死亡的「黑死病」。