但没有人发现这种疾病的致病病毒。

But no one had ever found a pathogen in an animal sick with the disease.

youdao

错误突变理论引导了通过突变来控制致病病毒的策略。

Error catastrophe theory has led to a strategy of mutagenesis to control disease viruses.

youdao

这种二重性从一开始便存在，就在谁发现了艾滋病致病病毒问题上。

Such dualism was there from the beginning, in the question of who discovered the AIDS-causing virus.

youdao

So, that was a naturally occurring attenuated virus that could be produced into a vaccine that didn't cause the disease.

因为天花病毒存在天然的衰减病毒,这种衰减病毒可以用来,直接生产不致病的疫苗

耶鲁公开课 - 生物医学工程探索课程节选

But unlike the Cowpox virus, vaccinea, that we talked about before, this is the real disease causing agent.

但是同我们之前曾讨论过的,牛痘病毒疫苗的不同之处在于,这是可以直接致病的病毒

耶鲁公开课 - 生物医学工程探索课程节选

So, you couldn't introduce the live virus in because that would cause the disease not just immunity.

所以 不可以直接接种活体病毒,因为这会使人致病而不仅是引起免疫应答

耶鲁公开课 - 生物医学工程探索课程节选