世界上存在着许多种流感病毒,禽流感是其中的一大类,它们出现在鸟这样的禽类身上。各种病毒中只有非常少的一些能够成功地突破物种之间的生理阻碍,从动物身上传染给人类。最近让全世界感到恐慌的是,某些禽流感病毒感染了人类。比如,一种叫做H5N1型的禽流感病毒在过去5年中造成了348例病例,使60%的被感染者死亡。 There are many kinds of influenza viruses in the world. Bird flu is one of the major types, and they appear on birds such as birds. Only a very few of the various viruses successfully break through the physical barriers between species and spread from animals to humans. What has panicked the world recently is that some bird flu viruses infect humans. For example, a bird flu virus of the H5N1 type has caused 348 cases in the past five years, killing 60% of those infected.