/ˈvɪrʊl(ə)nt/ /ˈvɪrjʊl(ə)nt/ [veer-you-lent]
1 (of a disease or poison) extremely severe or harmful in its effects.
1.1 (of a pathogen, especially a virus) highly infective.
2 Bitterly hostile.
Late Middle English (originally describing a poisoned wound): from Latin virulentus, from virus ‘poison’ (see virus).
Memes spread through culture because they behave like a virus, caught by one connection after another. Sadly, some are also negatively virulent.