Related topics: swine flu , flu , influenza , bird flu , flu virus
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
Study reveals H1N1 unexpected weakness
Dec 10, 2009 |
4.8 / 5 (19) |
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The H1N1 influenza virus has been keeping a secret that may be the key to defeating it and other flu viruses as well.
New giant virus discovered
Dec 09, 2009 |
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Scientists in France have isolated a new giant virus that lurks inside amoeba and whose gene pool includes genetic material from other species.
Antarctic lake home to diverse community of viruses
Nov 11, 2009 |
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(PhysOrg.com) -- A study of the genetic structure of viruses in an Antarctic lake has revealed an astonishing genetic richness in the large number of viral families discovered.
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 ...
Study: Tanning beds definitely cause cancer
Jul 28, 2009 |
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(AP) -- International cancer experts have moved tanning beds and ultraviolet radiation into the top cancer risk category, deeming both to be as deadly as arsenic and mustard gas. For years, scientists have ...
New invention could revolutionize how diseases are diagnosed
Jul 24, 2009 |
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(PhysOrg.com) -- An award-winning invention by Stanford doctoral students Richard Gaster and Drew Hall may change who diagnoses diseases ranging from flu to the Human Immunodeficiency Virus. The invention, ...
Mystery solved: Scientists now know how smallpox kills
Dec 22, 2009 |
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A team of researchers working in a high containment laboratory at the Centers for Disease Control and Prevention in Atlanta, GA, have solved a fundamental mystery about smallpox that has puzzled scientists long after the ...
No such thing as 'junk RNA,' say Pitt researchers
Oct 13, 2009 |
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Tiny strands of RNA previously dismissed as cellular junk are actually very stable molecules that may play significant roles in cellular processes, according to researchers at the University of Pittsburgh School of Medicine ...
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 ...
Piece from childhood virus may save soldiers' lives
Sep 06, 2009 |
4.4 / 5 (9) |
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A harmless shard from the shell of a common childhood virus may halt a biological process that kills a significant percentage of battlefield casualties, heart attack victims and oxygen-deprived newborns, according to research ...
Scientists discover potential new drug delivery system
Aug 25, 2009 |
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(PhysOrg.com) -- Scientists at UC Santa Barbara have discovered a potential new drug delivery system. The finding is a biological mechanism for delivery of nanoparticles into tissue. The results are published ...
Scientists use virus to kill cancer cells while leaving normal cells intact
Dec 03, 2009 |
5 / 5 (7) |
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(PhysOrg.com) -- A virus that in nature infects only rabbits could become a cancer-fighting tool for humans. Myxoma virus kills cancerous blood-precursor cells in human bone marrow while sparing normal blood stem cells, a ...
Gene Hijacked By HIV Ancestor Suggests New Way to Block Viral Reproduction
Dec 07, 2009 |
4.9 / 5 (7) |
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(PhysOrg.com) -- An ancestor of the AIDS virus hijacked an entire gene, perhaps from some prehistoric cat it had infected, a gene that makes it much better able to infect humans, according to a study published ...
Scientists discover influenza's Achilles heel: Antioxidants
Oct 29, 2009 |
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As the nation copes with a shortage of vaccines for H1N1 influenza, a team of Alabama researchers have raised hopes that they have found an Achilles' heel for all strains of the flu—antioxidants. In an article appearing in ...
Tumor-attacking virus strikes with 'one-two punch'
Dec 01, 2009 |
5 / 5 (6) |
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Ohio State University cancer researchers have developed a tumor-attacking virus that both kills brain-tumor cells and blocks the growth of new tumor blood vessels.
