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
K-State Expert Says Fear Of H1N1 Amplifies Normal Anxiety About School, Offers Tips On How To Cope
Medicine & Health / Psychology & Psychiatry
Nov 06, 2009 |
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For university students, anxiety about grades is nothing new. But this year, students also may be anxious about the H1N1 flu virus and missing classes.
Newly Discovered Fat Molecule: An Undersea Killer with an Upside
Nov 05, 2009 |
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(PhysOrg.com) -- A chemical culprit responsible for the rapid, mysterious death of phytoplankton in the North Atlantic Ocean has been found by collaborating scientists at Rutgers University and the Woods Hole ...
Gene therapy technique slows ALD brain disease
Nov 05, 2009 |
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A strategy that combines gene therapy with blood stem cell therapy may be a useful tool for treating a fatal brain disease, French researchers have found. These findings appear in the 6 November 2009 issue ...
WHO: Swine flu virus is top strain worldwide
Nov 05, 2009 |
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(AP) -- The World Health Organization's flu chief said the swine flu virus has now become the predominant flu strain worldwide.
Scientists track swine flu virus for tiny changes that would cause big problems
Nov 04, 2009 |
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As the H1N1 flu virus spreads at breakneck speed, a team of scientists are close behind. They are watching its evolution through a cutting-edge technology in hopes of answering the question: Where did it come from -- and ...
Commercial pigs in Ind. test positive for H1N1
Nov 04, 2009 |
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(AP) -- The U.S. Department of Agriculture said Wednesday that pigs in a commercial herd in Indiana have tested positive for swine flu, making it the first time the virus has been found in such hogs.
Officials: Swine flu confirmed in Iowa cat
Nov 04, 2009 |
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(AP) -- The swine flu virus has been confirmed in a cat treated at the Iowa State University College of Veterinary Medicine.
Report on H1N1 cases in California shows hospitalization can occur at all ages, with many severe
Nov 03, 2009 |
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In contrast with some common perceptions regarding 2009 influenza A(H1N1) infections, an examination of cases in California indicates that hospitalization and death can occur at all ages, and about 30 percent of hospitalized ...
Hooks hijacked? New research shows how to block stealthy malware attacks
Technology / Computer Sciences
Nov 03, 2009 |
4.9 / 5 (13) |
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The spread of malicious software, also known as malware or computer viruses, is a growing problem that can lead to crashed computer systems, stolen personal information, and billions of dollars in lost productivity every ...
There's a speed limit to the pace of evolution, biologists say
Nov 02, 2009 |
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Researchers at the University of Pennsylvania have developed a theoretical model that informs the understanding of evolution and determines how quickly an organism will evolve using a catalogue of "evolutionary speed limits." ...
Extending treatment after liver transplant may benefit patients with hepatitis C recurrence
Nov 01, 2009 |
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Extending hepatitis C treatment for liver transplant patients beyond current practice results in high rates of clearance of the hepatitis C virus from the blood, as well as a low rate of relapse, according to a Henry Ford ...
Swine flu deaths jump by 700 in a week: WHO
Oct 30, 2009 |
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The number of swine flu deaths jumped by 700 in a week, reaching more than 5,700 worldwide since the virus was first uncovered in April, World Health Organisation data indicated Friday.
Breakthrough in fight against Hendra virus
Oct 30, 2009 |
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(PhysOrg.com) -- There has been a breakthrough in the fight against the deadly Hendra virus following the development of a treatment which shows great potential to save the lives of people who become infected ...
Scientists Propose New Explanation for Flu Virus Antigenic Drift
Oct 29, 2009 |
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(PhysOrg.com) -- Influenza viruses evade infection-fighting antibodies by constantly changing the shape of their major surface protein. This shape-shifting, called antigenic drift, is why influenza vaccines ...
Two-pronged protein attack could be source of SARS virulence
Oct 29, 2009 |
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Ever since the previously unknown SARS virus emerged from southern China in 2003, University of Texas Medical Branch at Galveston virologists have focused on finding the source of the pathogen's virulence — its ability to ...
