Virulence

Virulence means disease severity. The word virulent, meaning a poisoned wound, derives from the Latin word virulentus. Virulence is the comparative ability of a pathogen to defeat a host's defenses and cause disease or damage. A pathogen is an organism, eg, a bacterium or virus, that harms its host and causes illness. As a host, the level of damage caused by a microbe or a virus in animals refers to virulence. The virulence factors are determined by the pathogenicity, ie, the ability of an organism to cause disease. An example of a virulence factor is the capability of microbes to multiply within their host cells. These factors are critical to epidemiology, the process used to find the causes of diseases in a population, mainly when tracking a novel pathogenic strain, eg, the delta variant of coronavirus, a highly virulent, more harmful, and even lethal to its host. In biology, virulence is the extent to which a pathogenic organism can cause disease. The pathogenic ability of an organism to infect a host-resistant plant also often refers to virulence. From an ecological standpoint, virulence is the loss of resistance a parasite induces upon its host. Ecology studies the associations between living organisms, including humans, and their physical environment. Virulence can be understood in terms of proximal causes, ie, those specific traits of the pathogen that assist in making the host ill, and eventual causes, which refer to the evolutionary pressures that lead to virulent features taking place in a pathogen strain. The meanings of virulence and pathogenicity are related but different. Whereas pathogenicity is defined as the ability of a pathogen to cause disease, virulence refers to the degree of pathogenicity of a particular organism. [M. Anwar Hossain]