Virulence

The ability of any agent of infection to produce disease. The virulence of a microorganism (such as a bacterium or virus) is a measure of the severity of the disease it is capable of causing. The adjective virulent implies extremely noxious, damaging, deleterious, disease-causing (pathogenic). Marked by a rapid, severe, and malignant course. Poisonous, venomous. The word “virulence” comes from the Latin “virulentia” from “virus” meaning a slimy liquid, particularly one that is foul and poisonous.

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The disease-evoking severity of a pathogen; numerically expressed as the ratio of the number of cases of overt infection to the total number infected, as determined by immunoassay. [L. virulentia, fr. virulentus, poisonous]

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vir·u·lence 'vir-(y)ə-lən(t)s n the quality or state of being virulent: as

a) relative severity and malignancy <ameliorate the \virulence of a disease>

b) the relative capacity of a pathogen to overcome body defenses compare INFECTIVITY

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n.

the disease-producing (pathogenic) ability of a microorganism. See also attenuation.

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vir·u·lence (virґu-ləns) [L. virulentia, from virus poison] the degree of pathogenicity of a microorganism as indicated by the severity of the disease produced and its ability to invade the tissues of a host. It is measured experimentally by the median lethal dose (LD₅₀) or median infective dose (ID₅₀). 1. by extension, the competence of any infectious agent to produce pathologic effects.