Flu is highly infectious.

流感的传染性很高。

《牛津词典》

But when it has, the bird flu has proved to be a highly infectious and potent disease, that is fatal 60 percent of the time.

但这种禽流感病毒已经被证明是一种高传染性且强有力的疾病，60%将是致命的。

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Controversial research is set to resume on artificially creating a new highly contagious form of the H5N1 bird flu virus, which could be spread by humans.

科学家称将重启对一种新型高传染性H5N1禽流感病毒的研究，这种病毒可以通过人际传播，此举引起广泛争议。

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Secondly, the 2009 H1N1 lacks a gene that is present in highly virulent flu viruses, such as the one in 1918.

CNN: Swine flu, part II: What's in store in the months to come

Norovirus is highly contagious, even moreso than the flu.

FORBES: Norovirus: The Bug That Is Presently Making So Many Of Us Sick