Related topics: proceedings of the national academy of sciences , cells , hiv , bird flu , h5n1
Virus
hideI: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (−)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses
A virus (from the Latin virus meaning toxin or poison) is a microscopic infectious agent that can reproduce only inside a host cell. Viruses infect all types of organisms: from animals and plants, to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, more than 5,000 types of virus have been described in detail, although most types of virus remain undiscovered. Viruses are ubiquitous, as they are found in almost every ecosystem on Earth, and are the most abundant type of biological entity on the planet. The study of viruses is known as virology, and is a branch of microbiology.
Viruses consist of two or three parts: all viruses have genes made from either DNA or RNA, long molecules that carry genetic information; all have a protein coat that protects these genes; and some have an envelope of fat that surrounds them when they are outside a cell. Viruses vary in shape from simple helical and icosahedral shapes, to more complex structures. They are about 1/100th the size of bacteria. The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.
Viruses spread in many ways; plant viruses are often transmitted from plant to plant by insects that feed on sap, such as aphids, while animal viruses can be carried by blood-sucking insects. These disease-bearing organisms are known as vectors. Influenza viruses are spread by coughing and sneezing, and others such as norovirus, are transmitted by the faecal-oral route, when they contaminate hands, food, or water. Rotaviruses are often spread by direct contact with infected children. HIV is one of several viruses that are transmitted through sexual contact.
Not all viruses cause disease, as many viruses reproduce without causing any obvious harm to the infected organism. Viruses such as hepatitis B can cause life-long or chronic infections, and the viruses continue to replicate in the body despite the hosts' defence mechanisms. In some cases, these chronic infections might be beneficial as they might increase the immune system's response against infection by other pathogens. However, in most cases viral infections in animals cause an immune response that eliminates the infecting virus. These immune responses can also be produced by vaccines that give lifelong immunity to a viral infection. Microorganisms such as bacteria also have defences against viral infection, such as restriction modification systems. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat both life-threatening and more minor infections.
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News tagged with virus
Mutation found in swine flu virus: WHO
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The World Health Organisation said Friday that a mutation had been found in samples of the swine flu virus taken following the first two deaths from the pandemic in Norway.
Preventing H1N1 spread to health care workers: Dilemma, debate and confusion
Nov 19, 2009 |
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A commentary in the December issue of The Lancet Infectious Diseases brings to light the gaps in knowledge on the transmission of a common pathogen - the influenza virus - and its impact on decisions about how best to pro ...
New research helps explain why bird flu has not caused a pandemic
Nov 19, 2009 |
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(PhysOrg.com) -- Bird flu viruses would have to make at least two simultaneous genetic mutations before they could be transmitted readily from human to human, according to research published today in PLoS ON ...
Toward explaining why hepatitis B hits men harder than women
Nov 18, 2009 |
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Scientists in China are reporting discovery of unusual liver proteins, found only in males, that may help explain the long-standing mystery of why the hepatitis B virus (HBV) sexually discriminates -- hitting ...
UK police make 2 Trojan computer virus arrests
Nov 18, 2009 |
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(AP) -- A couple suspected of helping spread some of the Internet's most aggressive computer viruses has been arrested in the English city of Manchester, police said Wednesday.
Researchers Examine How Viruses Destroy Bacteria
Nov 18, 2009 |
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Viruses are well known for attacking humans and animals, but some viruses instead attack bacteria. Texas A&M University researchers are exploring how hungry viruses, armed with transformer-like weapons, attack bacteria, which ...
New effort probes how two groups of viruses cause disease
Nov 18, 2009 |
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(PhysOrg.com) -- Purdue University is leading a team of researchers in a federally funded effort aimed ultimately at developing better vaccines and antiviral drugs against two types of disease-causing viruses ...
Imaging study shows HIV particles assembling around its genome
Medicine & Health / HIV & AIDS
Nov 17, 2009 |
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(PhysOrg.com) -- The genesis of one the planet's most lethal viruses, HIV, has been caught on tape. New imaging experiments show individual HIV genomes -- strands of RNA — docking on the inner membrane of an infected cell ...
British town to offer free wi-fi to all residents
Nov 17, 2009 |
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Swindon has become the first place in Britain to offer free wireless Internet access to all its 186,000 residents, in what is thought to be the first such scheme, officials said on Tuesday.
Scientists find previous seasonal flu infections may provide some level of H1N1 immunity
Nov 16, 2009 |
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Researchers at the La Jolla Institute for Allergy & Immunology have found that previous influenza infections may provide at least some level of immunity to the H1N1 "swine" flu.
Study shows link between influenza virus and fever
Nov 16, 2009 |
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One feature of the "new influenza" is a sudden rise in temperature. Up to now it was not exactly understood how this reaction occurs. Scientists at the University of Bonn and the Technical University of Munich, Germany, have ...
Scientists put interactive flu tracking at public's fingertips
Nov 16, 2009 |
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New methods of studying avian influenza strains and visually mapping their movement around the world will help scientists more quickly learn the behavior of the pandemic H1N1 flu virus, Ohio State University ...
Good hygiene goes a long way toward keeping pets, people healthy
Nov 13, 2009 |
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(PhysOrg.com) -- People may not be the only ones susceptible to the H1N1 virus this year - family pets also can fall victim to the influenza.
Shape of things to come: Structure of HIV coat could lead to new drugs
Medicine & Health / HIV & AIDS
Nov 12, 2009 |
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Structural biologists at the University of Pittsburgh School of Medicine have described the architecture of the complex of protein units that make up the coat surrounding the HIV genome and identified in it a "seam" of functional ...
No-entry zones for AIDS virus
Medicine & Health / HIV & AIDS
Nov 12, 2009 |
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The AIDS virus inserts its genetic material into the genome of the infected cell. Scientists of the German Cancer Research Center have now shown for the first time that the virus almost entirely spares particular ...
