病菌对人类的威胁与祸害由来已久,早在远古的狩猎时代,寄生物已不断地滋扰人类。当某种传染病菌首度侵入缺乏罹患该病经验的族群时,往往会暴发大流行,造成死伤惨重。十四世纪欧洲的黑死病,就是代表性的例子。传染病与人类的历史息息相关、彼此互动;传染病造成的人口大量损失,可能扭转战争局势, Pathogens have a long history of threats and scourges to humans. As early as the ancient hunting age, parasites were constantly nuisance to humans. When a certain kind of infectious disease first invades the ethnic group lacking in the experience of the disease, a pandemic will often occur, causing heavy casualties. The black death in Europe in the fourteenth century is a representative example. Infectious diseases are closely linked with the history of mankind and interact with each other. The huge loss of population caused by infectious diseases may reverse the war situation,