A scientist friend asked about the layperson's use of the word virulent. To our correspondent, the distinction between virulent and pathogenic is clearcut: something pathogenic involves pathogens, specific causative agents (as a bacterium or virus) that cause disease. Virulent, in her mind, is reserved for the virus that causes infectious disease. (来源：专业英语学习网站 http://www.EnglishCN.com)

So why, she wants to know, has the adjectival virulent spread like wildfire in the lexicon? Virulent describes something "marked by a rapid, severe, and malignant course;" something "extremely poisonous or venomous;" something "full of malice" or "malignant;" or something "objectionably harsh or strong."

We can't explain exactly why one word spreads and another doesn't, but our investigation did turn up some interesting data. First, pathogenesis and its linguistic offspring are 19th century coinages of New Latin and International Scientific Vocabulary origin that describe the origination and development of a disease. Virulent, on the other hand, dates back to the14th century, and its expanded senses developed relatively quickly.

Virulent comes from the Latin virus meaning "slimy liquid; poison; stench." Back before microscopes, when scientists and doctors were unable to establish the cause of various illnesses, the term virus (which originally meant "venom emitted by a poisonous animal") was borrowed as a name for a disease germ, or the causative agent of an infectious disease.