But this past Sunday, she gave me a bit of an opening: in response to a question as to whether there are any beneficial viruses. Her response:
No. Bacteria are living one-celled microorganisms. By contrast, viruses aren’t alive in a strict sense: They are the ultimate parasites and cannot replicate without a host. They invade the cells of animals, plants and even bacteria, then either lie dormant or get into the driver’s seat and cause changes that disrupt normal cell functioning, the very essence of disease.
The first two sentences and most of the third are dead on the money: bacteria are unicellular organisms, viruses aren't considered alive & invade other cells, where they can lie dormant or immediately go crazy. However, that last bit is the clincher. Apparently Ms. vos Savant is unaware that in the bacterial world there are examples of viruses benefiting their host by bringing along useful genetic stuff. Diptheria is one example, in which the toxin (which presumably helps the bacterial host) is encoded by a virus (phage).
Are there examples outside of bacteria? I don't know of any, but I'm hardly up on my viruses. Moreover, how would we know? Suppose there were viruses which were simply neutral (or nearly so), would we have ever detected them?
Also, in a broader sense some of those phage out there may be an important ecological control on bacterial nasties. So this could be another class of "beneficial" viruses.
Just because you are a parasite doesn't mean you're guaranteed bad!