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 viruses
Fighting drug-resistant flu viruses
Jul 15, 2009 |
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Amid reports that swine flu viruses are developing the ability to shrug off existing antiviral drugs, scientists in Japan are reporting a first-of-its kind discovery that could foster a new genre of antivirals ...
New study describes risk of mobile phone virus attacks
Jun 11, 2009 |
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Traditional cell phones have been immune to viruses because they lack standardized operating systems. However, as smart phones rapidly increase in market share, viruses pose a serious threat to mobile communications.
Cancer Researchers Identify New Mutant Genes
Jun 03, 2009 |
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(PhysOrg.com) -- University of New Mexico Cancer Center researchers have identified a genetic mutation underlying one of the most common childhood cancers, acute lymphoblastic leukemia (ALL). The discovery could lead to more ...
Jeepers creepers: Climate change threatens endangered honeycreepers
May 26, 2009 |
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As climate change causes temperatures to increase in Hawaii's mountains, deadly non-native bird diseases will likely also creep up the mountains, invading most of the last disease-free refuges for honeycreepers - a group ...
InDevR's FluChip detects, distinguishes swine-origin H1N1 from human influenza viruses
May 05, 2009 |
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InDevR, a small biotech company in Boulder, CO, and the Influenza Division of the Centers for Disease Control and Prevention (CDC) in Atlanta confirmed today that the M gene version of InDevR's FluChip can detect swine-origin ...
Flu could flourish in southern hemisphere winter
May 04, 2009 |
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(AP) -- Southern hemisphere countries that have largely escaped swine flu infections could soon become more vulnerable, experts warn, as the approaching winter brings with it an elevated risk of the virus ...
Ancestor of HIV in primates may be surprisingly young
Medicine & Health / HIV & AIDS
May 01, 2009 |
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The ancestors of the simian immunodeficiency viruses (SIVs) that jumped from chimpanzees and monkeys, and ignited the HIV/AIDS pandemic in humans, have been dated to just a few centuries ago. These ages are substantially ...
Pandemic study of 1918 outbreak provides background, death rates for 14 European countries
Apr 30, 2009 |
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A French study of the 1918-1919 influenza pandemic, which analysed mortality rates in approximately three-quarters of the European population, has concluded that it is unlikely that the virus, often described as Spanish Flu, ...
FluChip technology licensed to combat deadly flu virus
Apr 28, 2009 |
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InDevR, a small biotech company in Boulder, CO, announced today that they have licensed the FluChip technology from the University of Colorado. The FluChip was invented by a joint team of scientists at the University of ...
Universal flu vaccine holds promise
Apr 27, 2009 |
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An influenza vaccine that protects against death and serious complications from different strains of flu is a little closer to reality, Saint Louis University vaccine researchers have found.
First broad spectrum anti-microbial paint to kill 'superbugs'
Apr 20, 2009 |
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Scientists in South Dakota are reporting development of the first broad-spectrum antimicrobial paint, a material that can simultaneously kill not just disease-causing bacteria but mold, fungi, and viruses. ...
Once smartphones become truly common, so will the viruses that attack them
Technology / Computer Sciences
Apr 14, 2009 |
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(PhysOrg.com) -- Northeastern researchers say that it’s only a matter of time before computer viruses attack smartphones, like the Blackberry and iPhone, on a massive scale. But their study may also hold the ...
Low-tech tools take out phones in Silicon Valley
Apr 11, 2009 |
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(AP) -- Forget, for a moment, computer viruses and sophisticated cybercrimes. A hacksaw and a few other tools were probably all it took for someone to sever eight fiber-optic cables in Silicon Valley this ...
Mass Extinctions, Ancient Viruses May Hold Clues to Life’s Origins
Apr 03, 2009 |
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(PhysOrg.com) -- Mass extinctions occur repeatedly, though irregularly, throughout Earth’s history, and occasionally these extinctions have been devastating to life on our planet - or have they? Extinction ...
West Nile virus studies show how star-shaped brain cells cope with infection
Mar 31, 2009 |
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A new study published as the cover article for the April 2009 issue of The FASEB Journal promises to give physicians new ways to reduce deadly responses to viral infections of the brain and spinal cord. In the report, scient ...
