virulence

Examples of virulence in the following topics:

• Regulating Virulence

  • Virulence regulation is a combination of the specific traits of the pathogen and the evolutionary pressures that lead to virulent traits.
  • In an ecological context, virulence can be defined as the host's parasite-induced loss of fitness.
  • The evolution of virulence in pathogens is a balance between the costs and benefits of virulence to the pathogen.
  • If the pathogen's virulence kills the host and interferes with its own transmission to a new host, virulence will be selected against.
  • But as long as transmission continues despite the virulence, virulent pathogens will have the advantage.

• Ecology, Epidemiology, and Evolution of Pathogens

  • Optimal virulence is a concept relating to the ecology of hosts and parasites.
  • However, the host, being the parasite's resource and habitat in a way, suffers from this higher virulence.
  • Thus, there is a natural force providing pressure on the parasite to "self-limit" its virulence.
  • The idea is then, that there exists an equilibrium point of virulence, where parasite's fitness is highest.
  • Any movement on the virulence axis, towards higher or lower virulence, will result in lower fitness for the parasite, and this will be selected against.

• Virulent Bacteriophages and T4

  • T-4 bacteriophage is a virulent bacteriophage that infects E. coli bacteria; virulent bacteriophages have a lytic life cycle.
  • The pathogenicity of an organism is determined by its virulence factors.
  • Virus virulence factors determine whether an infection will occur and how severe the resulting viral disease symptoms are.
  • Virulent viruses such as HIV, which causes AIDS, have mechanisms for evading host defenses.
  • Summarize how the T4 life cycle serves as a model for viral virulence

• Pathogenicity Islands and Virulence Factors

  • These mobile genetic elements may range from 10-200 kb, and may encode genes contributing to the virulence of the respective pathogen.
  • PAIs carry genes encoding one or more virulence factors, including, but not limited to, adhesins, toxins, or invasins.
  • They can be transferred as a single unit to new bacterial cells, thus conferring virulence to formerly benign strains.

• Pathogenicity Islands

  • Pathogenenicity islands are discrete genetic loci that encode factors which make a microbe more virulent.
  • These mobile genetic elements may range from 10-200 kb and encode genes which contribute to the virulence of the respective pathogen.
  • Pathogenicity islands carry genes encoding one or more virulence factors, including, but not limited to, adhesins, toxins, or invasins.
  • They can be transferred as a single unit to new bacterial cells, thus conferring virulence to formerly benign strains.

• Colonization and Growth

  • Some virulent bacteria produce special proteins that allow them to colonize parts of the host body.
  • The virulence of various strains of Helicobacter pylori tends to correlate with the level of production of urease.
  • Non-pathogenic organisms can become pathogenic given specific conditions and even the most virulent organism requires certain circumstances to cause a compromising infection.
  • The variables involved in the outcome of a host becoming inoculated by a pathogen and the ultimate outcome include: the route of entry of the pathogen and the access to host regions that it gains, the intrinsic virulence of the particular organism, the quantity or load of the initial inoculant, and the immune status of the host being colonized.

• Identification of Microbes Based on Molecular Genetics

  • Genes that satisfy molecular Koch's postulates are often referred to as virulence factors (i.e., what makes the pathogen virulent).
  • Once virulent factors have been identified, it is possible to develop a vaccine against the factors. illustrates how the avian flu vaccine was developed using reverse genetic techniques.
  • Testing a candidate virulence gene requires a relevant animal model of the disease being examined and the ability to genetically manipulate the microorganism that causes the disease.

• Tularemia

  • A Gram-negative, nonmotile coccobacillus, the bacterium has several subspecies with varying degrees of virulence.
  • The most important of these is F. tularensis tularensis (Type A), which is found in lagomorphs (rabbits and similar animals) in North America, and it is highly virulent in humans and domestic rabbits.
  • It is less virulent for humans and rabbits.

• Whooping Cough

  • B. pertussis has the ability to inhibit the function of a host's immune system, through virulence factors.
  • Its virulence factors include pertussis toxin, filamentous hæmagglutinin, pertactin, fimbria, and tracheal cytotoxin.

• Adherence

  • Adhesins are a type of virulence factor.
  • Fimbriae are believed to be involved in attachment to solid surfaces or to other cells, and are essential for the virulence of some bacterial pathogens.