(vir'yŭ-lĕns )

[L. virulentia, stench]

1. The relative power of an agent or a microorganism to cause harm or disease. Properties that influence the virulence of an organism include 1) the strength of its adhesion molecules, which link it to the target cell; 2) its ability to secrete enzymes or exotoxins that damage target cells, or endotoxins that interfere with the body's normal regulatory systems; and 3) its ability to inhibit or evade the actions of the immune system and their chemical mediators.

   SEE: immunocompetence; immunocompromised.

2. Of a disease, the property of being virulent; venomousness.

   SEE: attenuation.