virus

(noun)

a submicroscopic infectious organism, now understood to be a non-cellular structure consisting of a core of DNA or RNA surrounded by a protein coat

Related Terms

Examples of virus in the following topics:

  • Virus Classification

    • However, these earlier classification methods grouped viruses based on which features of the virus they were using to classify them.
    • The virus core contains the genome or total genetic content of the virus.
    • For example, the tobacco mosaic virus has a naked helical capsid .
    • (a) Rabies virus has a single-stranded RNA (ssRNA) core and an enveloped helical capsid, whereas (b) variola virus, the causative agent of smallpox, has a double-stranded DNA (dsDNA) core and a complex capsid.
    • The capsid of the (a) polio virus is naked icosahedral; (b) the Epstein-Barr virus capsid is enveloped icosahedral; (c) the mumps virus capsid is an enveloped helix; (d) the tobacco mosaic virus capsid is naked helical; and (e) the herpesvirus capsid is complex.

  • Vaccines and Anti-Viral Drugs for Treatment

    • Vaccines and anti-viral drugs can be used to inhibit the virus and reduce symptoms in individuals suffering from viral infections.
    • The concept behind this is that by giving the vaccine, immunity is boosted without adding more disease-causing virus.
    • For most viruses, these drugs can inhibit the virus by blocking the actions of one or more of its proteins.
    • Thus, Tamiflu inhibits the spread of virus from infected to uninfected cells.
    • By attacking the virus at different stages of its replicative cycle, it is much more difficult for the virus to develop resistance to multiple drugs at the same time.

  • Steps of Virus Infections

    • A virus must use cell processes to replicate.
    • The symptoms of viral diseases result from the immune response to the virus, which attempts to control and eliminate the virus from the body and from cell damage caused by the virus.
    • Plant and animal viruses can enter through endocytosis, in which the cell membrane surrounds and engulfs the entire virus.
    • In influenza virus infection, glycoproteins attach to a host epithelial cell.
    • As a result, the virus is engulfed.

  • Animal Viruses

    • Other viruses cause long-term chronic infections, such as the virus causing hepatitis C, whereas others, like herpes simplex virus, cause only intermittent symptoms.
    • In hepatitis C infections, the virus grows and reproduces in liver cells, causing low levels of liver damage.
    • As mentioned, herpes simplex virus can remain in a state of latency in nervous tissue for months, even years.
    • As the virus "hides" in the tissue and makes few if any viral proteins, there is nothing for the immune response to act against; immunity to the virus slowly declines.
    • Latent infections are common with other herpes viruses as well, including the varicella-zoster virus that causes chickenpox.

  • Vaccines and Immunity

    • Vaccinations prevent viruses from spreading by building immunity to the virus.
    • While we do have limited numbers of effective antiviral drugs, such as those used to treat HIV and influenza, the primary method of controlling viral disease is by vaccination, which is intended to prevent outbreaks by building immunity to a virus or virus family .
    • Vaccines may be prepared using live viruses, killed viruses, or molecular subunits of the virus.
    • Live vaccines are usually made by attenuating (weakening) the "wild-type" (disease-causing) virus by growing it in the laboratory in tissues or at temperatures different from what the virus is accustomed to in the host.
    • Vaccinations are designed to boost immunity to a virus to prevent infection.

  • Immunodeficiency

    • Human immunodeficiency virus infection / acquired immunodeficiency syndrome (HIV/AIDS), is a disease of the human immune system caused by infection with human immunodeficiency virus (HIV) .
    • After the virus enters the body, there is a period of rapid viral replication, leading to an abundance of virus in the peripheral blood.
    • During primary infection, the level of HIV may reach several million virus particles per milliliter of blood.
    • The CD8+ T cell response is thought to be important in controlling virus levels, which peak and then decline, as the CD4+ T cell counts recover.
    • During primary infection, the level of HIV may reach several million virus particles per milliliter of blood.

  • Evolution of Viruses

    • The evolution of viruses is speculative as they do not fossilize; biochemical and genetic information is used to create virus histories.
    • However, viruses do not fossilize, so researchers must conjecture by investigating how today's viruses evolve and by using biochemical and genetic information to create speculative virus histories.
    • While most findings agree that viruses don't have a single common ancestor, scholars have yet to find one hypothesis about virus origins that is fully accepted in the field .
    • The emerging field called virus molecular systematics attempts to do just that through comparisons of sequenced genetic material.

  • Viral Morphology

    • Many plant viruses are filamentous, including TMV (tobacco mosaic virus).
    • Non-enveloped viruses also include those that cause polio (poliovirus), plantar warts (papillomavirus), and hepatitis A (hepatitis A virus).
    • The virus core contains the genome or total genetic content of the virus.
    • Viral genomes tend to be small, containing only those genes that encode proteins that the virus cannot obtain from the host cell.
    • The KSHV virus binds the xCT receptor on the surface of human cells.

  • Discovery and Detection of Viruses

    • Virions, single virus particles, are very small, about 20–250 nanometers in diameter.
    • These individual virus particles are the infectious form of a virus outside the host cell.
    • It was not until the development of the electron microscope in the late 1930s that scientists got their first good view of the structure of the tobacco mosaic virus (TMV) and other viruses .
    • The surface structure of virions can be observed by both scanning and transmission electron microscopy, whereas the internal structures of the virus can only be observed in images from a transmission electron microscope.
    • In these transmission electron micrographs, (a) a virus is dwarfed by the bacterial cell it infects, while (b) these E. coli cells are dwarfed by cultured colon cells.

  • Plant Viruses

    • For many plant viruses to be transferred from plant to plant, damage to some of the plants' cells must occur to allow the virus to enter a new host.
    • Symptoms of viral diseases vary according to the virus and its host.
    • Some viruses that infect agricultural food plants include the name of the plant they infect, such as tomato spotted wilt virus, bean common mosaic virus, and cucumber mosaic virus.
    • In plants used for landscaping, two of the most common viruses are peony ring spot and rose mosaic virus.
    • There are far too many plant viruses to discuss each in detail, but symptoms of bean common mosaic virus result in lowered bean production and stunted, unproductive plants.