Virulent means extremely harmful, or full of bitter hostility. A virulent strain, virulent criticism, virulently opposed.
In medicine it is technical and means how much damage an organism does once it has infected somebody, which is not the same as how easily it spreads. The figurative sense is about the tone of an attack.
1adjectivevirulentExtremely harmful, or full of bitter hostility.
“The newspaper launched a virulent attack on the minister's character.”
virulent is a quality.
Latin virulentus means poisonous, from virus, which first meant a poison or slimy liquid.
Proto-Indo-European
*wisós
French
virulent
Proto-Indo-European
*wisós — poison; slime; fluidity
Latin
vīrulentus — poisonous
Middle English
virulent — leaking or seeping pus, purulent; (of putrefaction) extremely severe (sense uncertain)
English, today
virulent
Built from
From Middle English virulent (“leaking or seeping pus, purulent; (of putrefaction) extremely severe (sense uncertain)”)verelent, virulente, borrowed from Latin vīrulentus (“poisonous”), from vīrus (“poison; venom; slime, slimy liquid; stinking smell; nasty taste”) (ultimately from Proto-Indo-European wisós (“poison; slime; fluidity”)) + -ulentus. Sense 4 (“of a pathogen: replicating within its host cell, then immediately causing it to undergo lysis”) is derived from French virulent, which was first used in this sense by the French biologist François Jacob (1920–2013) and his co-authors in a 1953 article.
Etymology from Wiktionary, CC BY-SA