它的背面去更远的演变，对不对？它概括跨越物种。
The farther back it goes in evolution, right? And it generalizes across species.
在极少数情况下，禽流感病毒已跨越物种屏障，感染人类。
On rare occasions, avian influenza viruses have crossed the species barrier to infect humans.
似乎这种病毒得以跨越物种的障碍传染到人类身上仅仅是出于人类的不幸。
Mankind, it seems, was just unlucky that this virus made the leap across the species barrier.
禽流感病毒具有高度物种特异性，但偶尔也跨越物种屏障，感染人类。
Avian influenza viruses are highly species-specific, but have, on rare occasions, crossed the species barrier to infect humans.
在跨越物种屏障感染人类的若干禽流感病毒中，H5N1导致的人类重症病例和死亡数目最多。
Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of cases of severe disease and death in humans.
也有报告称，某些禽流感病毒跨越物种界限传播，并导致人类和其他哺乳动物患病或亚临床感染。
Some of these AI viruses have also been reported to cross the species barrier and cause disease or subclinical infections in humans and other mammals.
现在没人知道激发一种既存的人体病菌有多么容易，不知道使病菌传染给另一种动物，帮助其跨越物种界限而传播有多么容易。
No one now knows how easy it would be to turbo-charge an existing human pathogen, or take one that infects another type of animal and assist its passage over the species barrier.
显然在试管里的情况是一种非自然状态，但是这项研究表明朊蛋白能在不借助于任何其它传染媒介的情况下跨越物种障碍。
The test tube is obviously an unnatural situation, but it shows that prions can leap the species barrier without the aid of any other infectious agent.
对于某些其他的迁徙物种来说，挑战变得更加复杂——因为跨越的距离更大、管辖范围更广、边界更广、沿途的危险也更多。
And with certain other migrating species, the challenge is complicated further—by vastly greater distances traversed, more jurisdictions, more borders, more dangers along the way.
1492年之后，在欧洲的轮船携带数千物种跨越大洋到达新家之时，这个世界的生态系统发生了碰撞并融合。
After 1492, the world's ecosystems collided and mixed as European vessels carried thousands of species to new homes across the oceans.
直到人们开始用船运输家具，这两个物种才跨越了地界。
It wasn't until we started shipping furniture that they crossed that divide.
跨越太平洋，距离赤道的最远端，就是阿拉斯加，一个蕴藏着大量冰川和众多珍稀物种的神奇之地。
Across the Pacific Ocean, far from the equator, Alaska is a state with numerous glaciers and countless rare species.
现在全世界众所周知，最近一种致命的流感新品种，跨越生物种的藩篱，从猪只传染到人类身上，而且墨西哥是新病毒袭击的全球第一个国家，显然也不是最后一个国家。
As the world now knows, Mexico was the first country affected by a new and deadly strain of influenza that has leapt the species barrier from pigs to people. The first, but not the last.
现在全世界众所周知，最近一种致命的流感新品种，跨越生物种的藩篱，从猪只传染到人类身上，而且墨西哥是新病毒袭击的全球第一个国家，显然也不是最后一个国家。
As the world now knows, Mexico was the first country affected by a new and deadly strain of influenza that has leapt the species barrier from pigs to people. The first, but not the last.
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