She left so quickly because some virulent virus, only four days.
因为某种致命的病毒，只用了4天，她就走了。
The virus did not mutate to a more virulent form.
病毒没有变异为致命性更强的形态。
If that evolution makes the virus more virulent, so much the worse for the host.
如果这种演变使得病毒毒性大增，寄主体质就会进一步遭到削弱。
This virus was both lethal and virulent.
这种病毒不但致死率高，而且毒性极强。
This virus was both lethal and virulent.
这种致病的病毒尚待查明。
This virus was both lethal and virulent.
这种致病的病毒尚待查明。
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