Using HPCs from umbilical cords and commercial LABS, the researchers demonstrated in test-tube experiments that the virus not only infected the cells but also could remain latent.

研究人员使用脐带中和盈利性实验室里的定向造血干细胞，通过在试管中进行试验演示出，病毒不但可以感染细胞而且还能保持潜伏状态。

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A person needs only to breathe in a small number of these germs to become infected (although only a small proportion of people will become infected with TB disease).

人只要吸入少量这些病菌，即受到感染(虽然只有少数人感染结核病)。

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According to a comprehensive study published in the journal Clinical Infectious Diseases, swine flu had infected only several dozen people in the world since it was first identified in 1930.

从发表在《临床传染病》上的综合研究来看，自1930年确认第一例猪流感传染人类的病例以来，世界上被感染的人只有数十位。

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The experts said you could get infected only if you sit within two rows of someone who is sick.

VOA: special.2009.07.14

This study shows that not only is it better for the person who is infected, but it helps that person from transmitting to the person that's their sexual partner, heterosexual partner."

VOA: special.2011.05.18

The outbreak of severe acute respiratory syndrome, or SARS, in Asia in 2003 only infected around 8, 000 people and killed about a tenth of these.

ECONOMIST: The spreading bird-flu menace reaches Europe | The

Users' machines will only be infected if they open and run the attachment bearing the worm.

BBC: The Bagle virus has tricked lots of people

It came back negative, which can happen with people infected only recently.

WSJ: TB's Global Resurgence Amplifies U.S. Risk