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Encyclopedia > Virulence

Virulence refers to the degree of pathogenicity of a microbe, or in other words the relative ability of a microbe to cause disease. The word virulent, which is the adjective for virulence, derives from the Latin word virulentus, which means "full of poison." From an ecological point of view, virulence can be defined as the host's parasite induced loss of fitness. A pathogen or infectious agent is a biological agent that causes disease or illness to its host. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... The term disease refers to an abnormal condition of an organism that impairs function. ... This article or section does not cite any references or sources. ... Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ...


Virulent bacteria

The ability of bacteria to cause disease is described in terms of the number of infecting bacteria, the route of entry into the body, the effects of host defense mechanisms, and intrinsic characteristics of the bacteria called virulence factors. Host-mediated pathogenesis is often important because the host can respond aggressively to infection with the result that host defense mechanisms do damage to host tissues while the infection is being countered. Virulence refers to the degree of pathogenicity of a microbe, or in other words the relative ability of a microbe to cause disease. ...


The virulence factors of bacteria are typically proteins or other molecules that are synthesized by protein enzymes. These proteins are coded for by genes in chromosomal DNA, bacteriophage DNA or plasmids. Figure 1: Schematic drawing of a bacterium with plasmids enclosed. ...



Methods by which pathogens cause disease

  • Adhesion. Many bacteria must first bind to host cell surfaces. Many bacterial and host molecules that are involved in the adhesion of bacteria to host cells have been identified. Often, the host cell receptors for bacteria are essential proteins for other functions.
  • Colonization. Some virulent bacteria produce special proteins that allow them to colonize parts of the host body. Helicobacter pylori is able to survive in the acidic environment of the human stomach by producing the enzyme urease. Colonization of the stomach lining by this bacterium can lead to Gastric ulcer and cancer. The virulence of various strains of Helicobacter pylori tends to corellate with the level of production of urease.
  • Invasion. Some virulent bacteria produce proteins that either disrupt host cell membranes or stimulate endocytosis into host cells. These virulence factors allow the bacteria to enter host cells and facilitate entry into the body across epithelial tissue layers at the body surface.
  • Immune response inhibitors. Many bacteria produce virulence factors that inhibit the host's immune system defenses. For example, a common bacterial strategy is to produce proteins that bind host antibodies. The polysaccharide capsule of Streptococcus pneumoniae inhibits phagocytosis of the bacterium by host immune cells.
  • Toxins. Many virulence factors are proteins made by bacteria that poison host cells and cause tissue damage. For example, there are many food poisoning toxins produced by bacteria that can contaminate human foods. Some of these can remain in "spoiled" food even after cooking and cause illness when the contaminated food is consumed. Some bacterial toxins are chemically altered and inactivated by the heat of cooking.

Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ... Binomial name Helicobacter pylori ((Marshall 1985) Goodwin 1989) Helicobacter pylori is a helical shaped Gram-negative bacterium that colonises the mucus layer of gastric epithelium in the stomach, and also the duodenum when it has undergone gastric metaplasia. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Helicobacter Pylori Urease drawn from PDB 1E9Z. Urease (EC 3. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... The term capsule in microbiology refers to a layer that lies outside the cell wall of bacteria. ... Binomial name Streptococcus pneumoniae (Klein 1884) Chester 1901 Streptococcus pneumoniae is a species of Streptococcus that is a major human pathogen. ... Phagocytosis is a form of endocytosis wherein large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a phagosome, or food vacuole. ... Foodborne illness or food poisoning is caused by consuming food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites. ... This article or section does not cite any references or sources. ...

Virulent virus

Viral virulence factors determine whether infection occurs and how severe the resulting viral disease symptoms are. Viruses often require receptor proteins on host cells to which they specifically bind. Typically, these host cell proteins are endocytosed and the bound virus then enters the host cell. Virulent viruses such as the AIDS virus (HIV) have mechanisms for evading host defenses. HIV causes a loss of T-cells and immunosuppression. Death results from opportunistic infections secondary to disruption of the immune system caused by the AIDS virus. Some viral virulence factors confer ability to replicate during the defensive inflammation responses of the host such as during virus-induced fever. Many viruses can exist inside a host for long periods during which little damage is done. Extremely virulent strains can eventually evolve by mutation and natural selection within the virus population inside a host. It has been suggested that Endocytic cycle be merged into this article or section. ... Species Human immunodeficiency virus 1 Human immunodeficiency virus 2 Human immunodeficiency virus (HIV) is a retrovirus that causes acquired immunodeficiency syndrome (AIDS, a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections). ... T cells belong to a group of white blood cells known as lymphocytes and play a central role in cell-mediated immunity. ... This article needs additional references or sources for verification. ... This article is about evolution in biology. ... Darwins illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. ...


See also Optimal virulence Optimal virulence is an idea relating to the ecology of hosts and parasites. ...


  Results from FactBites:
 
Virulence definition - Medical Dictionary definitions of popular medical terms (204 words)
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 word "virulence" comes from the Latin "virulentia" from "virus" meaning a slimy liquid, particularly one that is foul and poisonous.
Bird Flu - Bird flu is an infection caused by avian (bird) influenza (flu) viruses.
virulence: Definition, Synonyms and Much More from Answers.com (1100 words)
Virulence and pathogenicity are often used interchangeably, but virulence may also be used to indicate the degree of pathogenicity.
Virulence is often multifactorial, involving a complex interplay between the parasite and the host.
Virulence is either the relative pathogenicity or the relative ability to do damage to the host of an infectious agent.
  More results at FactBites »

 
 

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