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
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 ...
Researchers discover how mosquitoes avoid succumbing to viruses they transmit
Biology /
Dec 01, 2008 |
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Mosquitoes are like Typhoid Mary. They can spread viruses which cause West Nile fever, dengue fever, or yellow fever without themselves getting sick. Scientists long thought that the mosquito didn't care whether it had a ...
Common cold virus came from birds
Biology /
Nov 20, 2008 |
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A virus that causes cold-like symptoms in humans originated in birds and may have crossed the species barrier around 200 years ago, according to an article published in the December issue of the Journal of General Virology. ...
Image pinpoints all 5 million atoms in viral coat
Feb 16, 2009 |
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(PhysOrg.com) -- If a picture is worth a thousand words, then Rice University's precise new image of a virus' protective coat is seriously undervalued. More than three years in the making, the image contains ...
Research on viral origins suggests new definition of virus may be needed
Biology /
Feb 12, 2009 |
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(PhysOrg.com) -- The strange interaction of a parasitic wasp, the caterpillar in which it lays its eggs and a virus that helps it overcome the caterpillar’s immune defenses has some scientists rethinking the ...
MicroRNAs make for safer cancer treatments
Oct 26, 2008 |
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Viruses -- long regarded solely as disease agents -- now are being used in therapies for cancer. Concerns over the safety of these so-called oncolytic viruses stem from their potential to damage healthy tissues. Now Mayo ...
Research team finds immune molecule that attacks wide range of flu viruses
Feb 26, 2009 |
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The discovery of the molecule, an antibody known as CR6261, is good news for researchers who hope to design a flu vaccine that would give humans lifelong protection against a majority of influenza viruses. The antibody also ...
Taking the sting out of insect disease
Biology /
Oct 31, 2008 |
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(PhysOrg.com) -- University of Queensland researchers have made a discovery that could open up a new front in the fight against insect-transmitted diseases.
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.
Hebrew University study opening new route for combating viruses
Jun 25, 2008 |
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A unique technique for analyzing the function of microRNAs developed by a Hebrew University of Jerusalem doctoral student has led to the discovery of a new mechanism by which viruses evade the human immune system. This discovery ...
Researchers Engineer Self-Destructing Virus
Biology /
Jul 10, 2008 |
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University of Arizona researchers have sown the seeds of a virus' destruction in its own genetic code – or rather, in the genetic code of the organisms it seeks to infect. Their work could improve both the ...
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.
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 ...
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 ...
Detecting flu viruses in remote areas of the world
Jul 14, 2008 |
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Researchers in Ohio and New Mexico are reporting an advance in the quest for a fast, sensitive test to detect flu viruses — one that requires no refrigeration and can be used in remote areas of the world where ...
