[pohl]

How about this re-phrasing:

The most terrifying thing about prions is that they are infectious but not life: they can't be "killed" in the normal sense

While viruses are generally not considered to be alive, they are considered to be instances of life, aren't they?

[Double_Cast]

Of the 6 or 7 criteria biologists usually use to define life, viruses often fall short. E.g. viruses do not have their own metabolism.

Everyone has their own definition though. I remember reading a novel where life was defined simply as heredity, mutation, and adaptation. The second definition makes more sense to me, and implicitly includes viruses.

[djsumdog]

...and many viruses can't survive outside a host. Their structure can break apart. IIRC HIV is like that.

[pohl]

That doesn't quite capture it. There are lots of obligate parasites that aren't viruses, right?

https://en.wikipedia.org/wiki/Obligate_parasite

[ars]

That doesn't make them special. Fish can not survive without a host either (i.e. water).

[noselasd]

Water is not a host in the biological sense.

[ekianjo]

It makes them special since bacteria can survive in numerous environments where viruses are destroyed.