Is it farther or further?
c.1400, in reference to wounds, ulcers, etc., "full of corrupt or poisonous matter," from Latin virulentus "poisonous," from virus "poison" (see virus). Figurative sense of "violent, spiteful" is attested from c.1600. Related: Virulently.
virulent vir·u·lent (vēr'yə-lənt, vēr'ə-)
Extremely infectious, malignant, or poisonous. Used of a disease or toxin.
Capable of causing disease by breaking down protective mechanisms of the host. Used of a pathogen.
Intensely irritating, obnoxious, or harsh.