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
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 ...
Researchers find human protein that prevents H1N1 influenza infection
Dec 17, 2009 |
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Howard Hughes Medical Institute researchers have identified a naturally occurring human protein that helps prevent infection by H1N1 influenza and other viruses, including West Nile and dengue virus.
Compound found to safely counter deadly bird flu
Dec 21, 2009 |
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The specter of a drug-resistant form of the deadly H5N1 avian influenza is a nightmare to keep public health officials awake at night.
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.
Taming the flu: Researchers create map of interactions between flu virus and its human host
Dec 18, 2009 |
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(PhysOrg.com) -- There is no lack of worry this season over the flu, both the seasonal and H1N1 varieties, but there is a critical lack of understanding of the viruses that cause these illnesses. For years, ...
How flu succeeds: Investigators identify host factors that help multiple influenza strains thrive
Dec 22, 2009 |
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Investigators at Burnham Institute for Medical Research (Burnham), Mount Sinai School of Medicine (Mount Sinai), the Salk Institute for Biological Studies (Salk) and the Genomics Institute of the Novartis Research Foundation ...
Study reveals H1N1 unexpected weakness
Dec 10, 2009 |
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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.
Biological catch-22 prevents induction of antibodies that block HIV
Medicine & Health / HIV & AIDS
Dec 15, 2009 |
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Scientists seeking to understand how to make an AIDS vaccine have found the cause of a major roadblock. It turns out that the immune system can indeed produce cells with the potential to manufacture powerful HIV-blocking ...
2/3 of Australians unlikely to get vaccinated against swine flu
Dec 23, 2009 |
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Australia risks a serious swine flu (H1N1 influenza virus) outbreak with two-thirds (65 per cent) of unprotected Australians stating they're unlikely to get vaccinated against the disease in the next 12 months, according ...
Scientists use virus to kill cancer cells while leaving normal cells intact
Dec 03, 2009 |
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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 ...
Tumor-attacking virus strikes with 'one-two punch'
Dec 01, 2009 |
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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.
Global swine flu pandemic deaths pass 10,000: WHO
Dec 18, 2009 |
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The number of swine flu deaths worldwide passed the 10,000 mark about eight months after the pandemic strain was uncovered in April, reaching 10,582, World Health Organisation data showed Friday.
Gene Hijacked By HIV Ancestor Suggests New Way to Block Viral Reproduction
Dec 07, 2009 |
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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 ...
H1N1 influenza adopted novel strategy to move from birds to humans
Dec 08, 2009 |
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(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.
Research reveals further progress toward AIDS vaccine
Medicine & Health / HIV & AIDS
Dec 14, 2009 |
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(PHILADELPHIA) Researchers from Thomas Jefferson University are one step closer to developing a vaccine against the AIDS disease.
