perhaps the word "parasite" is more relevant to viruses.

AND how many times have we heard the phrase, in the context of vaccines and various types thereof, live virus vaccine? To distinguish one based on a completely incapacitated. And don't our scientists, and scientific publications, use the phrase?
More as a way of conveying information - as opposed to pedantic etymological data. And in that context the balance of correctness has to go with usage.

What we of this parish refer to as the Folk Process is ever more noticeable in language.

aprop pos of bacterium v virus. I heard on QI that an early cure for syphilis was to infect the patient with measles (?), (not that I believe much from that scientific myre).