Definition: The ability of an infectious microbe to cause disease.
Sometimes referred to as "pathogenicity," virulence typically refers to a quantitative measure of disease-causing ability. For example, virulence can be expressed as the number of microbes necessary to cause infection or death in 50% of individuals (ID50 and LD50, respectively).
The ability of a microbe to cause disease can be impacted by a number of factors, including a person's genetic makeup, as well as the genetic makeup of the microbes themselves. In addition, differences between individual immune responses (i.e., because of past exposure or vaccinations) can also alter the virulence of a microbe.
Pronunciation: VEER-you-LINSE
Also Known As: pathogenicity
