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
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.
New giant virus discovered
16 hours ago |
4.6 / 5 (10) |
8
Scientists in France have isolated a new giant virus that lurks inside amoeba and whose gene pool includes genetic material from other species.
Scientists use virus to kill cancer cells while leaving normal cells intact
Dec 03, 2009 |
5 / 5 (7) |
3
(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) |
0
(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 ...
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.
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 ...
'Rational drug design' identifies fragments of FDA-approved drugs relevant to emerging viruses
Dec 06, 2009 |
4.3 / 5 (3) |
1
A massive, data-crunching computer search program that matches fragments of potential drug molecules to the known shapes of viral surface proteins has identified several FDA-approved drugs that could be the basis for new ...
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.
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 ...
H1N1 influenza adopted novel strategy to move from birds to humans
Dec 08, 2009 |
5 / 5 (2) |
1
(PhysOrg.com) -- The 2009 H1N1 influenza virus used a new strategy to cross from birds into humans, a warning that it has more than one trick up its sleeve to jump the species barrier and become virulent.
Scientists reveal key structure from ebola virus
Dec 08, 2009 |
5 / 5 (2) |
0
Scientists at The Scripps Research Institute have determined the structure of a critical protein from the Ebola virus, which, though rare, is one of the deadliest viruses on the planet killing between 50 and 90 percent of ...
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 ...
Hajj devil stoning ritual biggest swine flu risk
Nov 28, 2009 |
3 / 5 (2) |
1
(AP) -- Millions of Muslim pilgrims, many wearing surgical masks, jostled together shoulder-to-shoulder furiously casting pebbles at stone walls representing the devil Saturday - the hajj ritual of highest ...
Good hygiene goes a long way toward keeping pets, people healthy
Nov 13, 2009 |
5 / 5 (1) |
0
(PhysOrg.com) -- People may not be the only ones susceptible to the H1N1 virus this year - family pets also can fall victim to the influenza.
Study shows link between influenza virus and fever
Nov 16, 2009 |
5 / 5 (1) |
0
One feature of the "new influenza" is a sudden rise in temperature. Up to now it was not exactly understood how this reaction occurs. Scientists at the University of Bonn and the Technical University of Munich, Germany, have ...
