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.
For more information about Virus, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with virus
Scientists use virus to kill cancer cells while leaving normal cells intact
Dec 03, 2009 |
5 / 5 (6) |
2
(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 ...
Tumor-attacking virus strikes with 'one-two punch'
Dec 01, 2009 |
5 / 5 (6) |
0
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.
Antarctic lake home to diverse community of viruses
Nov 11, 2009 |
4.9 / 5 (17) |
1
(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.
Newly Discovered Fat Molecule: An Undersea Killer with an Upside
Nov 05, 2009 |
4.8 / 5 (10) |
0
(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 ...
H1N1 pandemic virus does not mutate into 'superbug' in new lab study
Sep 01, 2009 |
4.5 / 5 (4) |
2
(PhysOrg.com) -- A laboratory study by University of Maryland researchers suggests that some of the worst fears about a virulent H1N1 pandemic flu season may not be realized this year, but does demonstrate ...
Scientists discover potential new drug delivery system
Aug 25, 2009 |
4.5 / 5 (8) |
0
(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 ...
New evidence: AIDS-like disease in wild chimpanzees
Jul 22, 2009 |
not rated yet |
1
An international consortium has found that wild chimpanzees naturally infected with Simian Immunodeficiency Viruses (SIV) - long thought to be harmless to the apes - can contract an AIDS-like syndrome and ...
Study suggests H1N1 virus more dangerous than suspected
Jul 13, 2009 |
4.1 / 5 (20) |
3
(PhysOrg.com) -- A new, highly detailed study of the H1N1 flu virus shows that the pathogen is more virulent than previously thought.
Knockouts in human cells point to pathogenic targets
Nov 26, 2009 |
5 / 5 (1) |
0
(PhysOrg.com) -- Whitehead researchers have developed a new approach for genetics in human cells and used this technique to identify specific genes and proteins required for pathogens.
Multitasking may be Achilles heel for hepatitis C
Nov 23, 2009 |
5 / 5 (2) |
0
(PhysOrg.com) -- Hepatitis C, a formidable virus that affects 130 million people worldwide, is nursing some pretty impressive bruises. By knocking out sections and subsections of one of its proteins, scientists reveal weak ...
Mutation found in swine flu virus: WHO
Nov 20, 2009 |
3.3 / 5 (3) |
0
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.
New research helps explain why bird flu has not caused a pandemic
Nov 19, 2009 |
5 / 5 (5) |
1
(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 ...
Imaging study shows HIV particles assembling around its genome
Medicine & Health / HIV & AIDS
Nov 17, 2009 |
5 / 5 (1) |
0
(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 ...
Scientists find previous seasonal flu infections may provide some level of H1N1 immunity
Nov 16, 2009 |
4 / 5 (1) |
0
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.
Scientists put interactive flu tracking at public's fingertips
Nov 16, 2009 |
2 / 5 (4) |
1
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 ...
