Of course, a behavior is so popular, just like a virus epidemic, certainly with trigger mechanism or incentive. Then how "Ice Bucket Challenge" spread?

当然，一项行为之所以流行，就跟病毒流行一样，肯定背后有起诱因或者触发机制，“挑战冰桶”是怎么这样传递下去的呢？

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If the virus had been capable of spreading through the air, or if one infected person had unknowingly entered a large population center, Ebola might have become a worldwide epidemic.

如果这种病毒能够通过空气传播，或者如果一名感染者在不知情的情况下进入了人口密集的地区，那么埃博拉可能已经成为一种全球流行病。

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With the COVID-19 epidemic hitting China, many of you might want to know more about the virus.

随着新冠肺炎疫情在中国爆发，你们中的很多人可能想了解更多有关病毒的信息。

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Scientists believe the H1N1 virus epidemic is no more dangerous than seasonal flu, and schools should act accordingly, Sebelius said.

CNN: Second U.S. death linked to swine flu, officials say

"The foot-and-mouth-disease virus epidemic in the UK in 2001 was disastrous and cost the economy billions of pounds in control measures and compensation, " explained Dr Bryan Charleston, Head of Livestock Viral Diseases Programme at the Pirbright Institute.

BBC: Synchrotron yields 'safer' vaccine

For decades, scientists have wondered why the virus is epidemic in the winter months but relatively absent the rest of the year.

FORBES: Coughing Mannequins Shed Light On Flu Transmission