virulent

Characterized by, causing, or promoting the rapid onset of severe illness. Used of a disease or toxin.

Capable of causing disease by aggressively interfering with the immune system of the host. Used of a pathogen.

Extremely hostile or malicious.

Full of virus; extremely poisonous or venomous.

Due to the action of a virus: as, a virulent inoculation.

Very bitter or spiteful; malignant: as, a virulent invective; a virulent libel.

Extremely poisonous or venomous; very active in doing injury.

Very bitter in enmity; actuated by a desire to injure; malignant.

highly infectious, malignant, or deadly.