A virulent disease or poison is dangerous and spreads or affects people very quickly.

A particularly virulent strain of flu has recently claimed a number of lives in the region. 一场有致命杀伤力的流感最近在这个地区夺去了许多人的生命。

full of hate and violent opposition

She is a virulent critic of US energy policy. 她是美国能源政策尖刻的批评者。