Portal:Viruses
Viruses are small infectious agents that can replicate only inside the living cells of an organism. Viruses infect all forms of life, including animals, plants, fungi, bacteria and archaea. They are found in almost every ecosystem on Earth and are the most abundant type of biological entity, with millions of different types, although only about 5,000 viruses have been described in detail. Some viruses cause disease in humans, and others are responsible for economically important diseases of livestock and crops.
Virus particles (known as virions) consist of genetic material, which can be either DNA or RNA, wrapped in a protein coat called the capsid; some viruses also have an outer lipid envelope. The capsid can take simple helical or icosahedral forms, or more complex structures. The average virus is about 1/100 the size of the average bacterium, and most are too small to be seen directly with an optical microscope.
The origins of viruses are unclear: some may have evolved from plasmids, others from bacteria. Viruses are sometimes considered to be a life form, because they carry genetic material, reproduce and evolve through natural selection. However they lack key characteristics (such as cell structure) that are generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life".
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Hepatitis C is an infectious disease affecting primarily the liver, caused by hepatitis C virus (HCV), an RNA virus of the Flaviviridae family which infects humans and chimpanzees. A "non-A non-B hepatitis" was postulated in the 1970s, and HCV was demonstrated in 1989. HCV is spread primarily by blood-to-blood contact associated with intravenous drug use in the developed world, and with poorly sterilised medical equipment and transfusions in the developing world. In about 80% of those infected, the virus persists in the liver, and around 10–30% of those infected will develop cirrhosis over 30 years. Some people with cirrhosis go on to develop liver failure, liver cancer or other complications.
An estimated 150–200 million people worldwide are infected with HCV. Hepatitis C causes 27% of cirrhosis cases and 25% of hepatocellular carcinoma (a form of liver cancer) worldwide, and is the leading reason for liver transplantation. The standard therapy for persistent infection is a combination of the antiviral drug ribavirin with pegylated interferon, sometimes plus one of the protease inhibitors, boceprevir or telaprevir. Overall, 50–80% of people treated are cured. No vaccine against hepatitis C is available.
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The MS2 bacteriophage was the first virus genome to be sequenced in 1976. Its capsid has an icosahedral structure made up from 180 copies of the coat protein.
Credit: Neil Ranson (7 June 2011)
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Viruses have infected plants and animals, including humans, for millions of years. Epidemics caused by viruses began when human behaviour changed during the Neolithic period. Previously hunter-gatherers, humans developed more densely populated agricultural communities, which allowed viruses to spread rapidly and subsequently to become endemic. Louis Pasteur and Edward Jenner were the first to develop vaccines to protect against viral infections, long before viruses were discovered. The sizes and shapes of viruses remained unknown until the invention of the electron microscope in the 1930s, when the science of virology gained momentum. In the 20th century, many diseases were found to be caused by viruses.
Viruses are the most abundant biological entity on Earth. Although scientific interest in them arose because of the diseases they cause, most viruses are beneficial. They have driven evolution by transferring genes across species, play important roles in ecosystems, and are essential to life.
16 March: Multiple new cases of Ebola virus are reported in Koropara, southern Guinea. WHO
10 March: The ongoing Middle East respiratory syndrome coronavirus outbreak (virus pictured) continues in Saudi Arabia and Qatar, with 46 new cases in February and March. WHO
8 March: Endogenous retrovirus Fc sequences, first identified in primates, are found in 11 different mammalian orders including rodents and carnivores. eLife
4 March: Endogenous retrovirus regulatory elements act as enhancers for interferon-induced immune genes in mammals. Science
4 March: Abnormal foetal ultrasound results are found in 12 of 42 pregnant women infected with Zika virus in Rio de Janeiro. NEJM
4 March: Zika virus is shown to productively infect human neural progenitor cells in vitro, causing cell death. Cell Stem Cell
1 March: The first dengue outbreak in Uruguay is reported, with 17 confirmed cases, mainly in Montevideo. WHO
27 February: The first chikungunya outbreak (virus pictured) in Argentina is reported, with 30 confirmed non-imported cases, mainly in Tartagal. WHO
29 February: A case-control study in 42 people with Guillain–Barré syndrome in Tahiti, French Polynesia in 2013–14 suggests that Zika virus might cause the syndrome. Lancet
24 February: A meta-analysis estimates that 2.3 million people, mainly those who inject drugs, are infected with both HIV and hepatitis C virus (HCV) and 82% of HIV+ injecting drug users are also infected with HCV. Lancet Infect Dis
24 February: In 82 Liberian Ebola survivors participating in the PREVAIL III study, frequent neurological problems are seen at least 6 months after the onset of symptoms. EurekAlert
23 February: Japanese encephalitis virus can be transmitted directly between pigs, without requiring a mosquito vector. Nat Commun
17 February: A novel gammaherpesvirus related to equine herpesvirus 2 is discovered in a cell line derived from the cave myotis bat (pictured). mSphere
16 February: An outbreak of Lassa fever occurs in Benin, with 71 suspected cases including 23 deaths; a Nigerian outbreak is also ongoing. WHO 1, 2 Template:/box-footer
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The 1918 flu pandemic was an unusually deadly influenza pandemic, the first of the two involving H1N1 influenza virus. The pandemic's geographic origin is unknown. Lasting from January 1918 until December 1920, it infected 500 million people across the entire globe, with a death toll of 50–100 million (3–5% of the world's population), making it one of the deadliest natural disasters of human history. It was also implicated in the outbreak of encephalitis lethargica in the 1920s.
Most influenza outbreaks disproportionately kill young, elderly or already weakened patients; in contrast the 1918 pandemic predominantly killed healthy young adults. Modern research suggests that the virus kills through a cytokine storm, an overreaction of the body's immune system. The strong immune reactions of young adults resulted in a more severe disease with a higher mortality rate, whereas the weaker immune systems of children and older adults resulted in fewer deaths.
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| “ | We live in a dancing matrix of viruses; they dart, rather like bees, from organism to organism, from plant to insect to mammal to me and back again, and into the sea, tugging along pieces of this genome, strings of genes from that, transplanting grafts of DNA, passing around heredity as though at a great party. | ” |
Template:/box-header Viruses & Subviral agents: elephant endotheliotropic herpesvirus • HIV • introduction to viruses
• Playa de Oro virus • poliovirus • prion • rotavirus • viruses
Diseases: colony collapse disorder • common cold • dengue fever • gastroenteritis • Guillain–Barré syndrome • hepatitis B • hepatitis C • herpes simplex • HIV/AIDS • influenza • meningitis • poliomyelitis • shingles • smallpox
Epidemiology & Interventions: 1918 flu pandemic • 2007 Bernard Matthews H5N1 outbreak • 2009 flu pandemic • HIV/AIDS in Malawi • polio vaccine
Host response: antibody • immune system • RNA interference
Social & Media: And the Band Played On • Contagion • "Flu Season" • Frank's Cock • Race Against Time • social history of viruses • "Steve Burdick" • "The Time Is Now"
People: Brownie Mary • Frank Macfarlane Burnet • Aniru Conteh • HIV-positive people • people with hepatitis C • poliomyelitis survivors • Ryan White Template:/box-footer
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Epstein–Barr virus (EBV) (also human herpesvirus 4) is a DNA virus in the Herpesviridae family which infects humans. The virion is around 120–180 nm in diameter. Like all herpesviruses, the capsid is surrounded by a protein tegument, as well as an envelope. The double-stranded DNA genome is about 192 kb with around 85 genes, making it one of the more complex viruses.
Transmission is in saliva and genital secretions. The virus infects epithelial cells in the mouth and pharynx and B cells of the immune system, producing virions by budding. EBV also becomes latent in B cells, possibly in the bone marrow, allowing the infection to persist lifelong. In the latent state, the linear genome is made circular and replicates separately from the host DNA as an episome. Reactivation is thought to be triggered by the B cell responding to other infections. EBV infection is almost ubiquitous. Infectious mononucleosis or glandular fever can occur when first infection is delayed until adolescence or adulthood. EBV is associated with some types of cancer, including Burkitt's lymphoma and nasopharyngeal carcinoma. In people with HIV, it can cause hairy leukoplakia and central nervous system lymphomas.
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- ...that extracts of pringamoza (pictured) have shown antiviral activity against herpes simplex?
- ...that the vaccine MVA-B has been found to create a resistance to HIV in 90% of the Phase I testers?
- ...that the Kunjin virus, which can be transmitted by mosquitoes and may cause encephalitis in humans, is named for an Indigenous Australian clan living near where the virus was first isolated?
- ...that the Gaussian network model has a wide range of applications from enzymes composed of a single domain, to large macromolecular assemblies, such as ribosomes and viral capsids?
- ...that Trinidadian virologist Joseph Lennox Pawan was the first person to show that rabies could be spread by vampire bats to other animals and humans?
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Edward Jenner (17 May 1749 – 26 January 1823) was an English physician and scientist from Berkeley, Gloucestershire, who was the pioneer of the smallpox vaccine.
Noting the common observation that milkmaids were generally immune to smallpox, Jenner postulated that the pus in the blisters that milkmaids received from cowpox (a similar but much less virulent disease) protected them from smallpox. Jenner tested his hypothesis by inoculating an eight-year-old boy with such pus. He subsequently repeatedly challenged the boy with variolous material, then the standard method of immunisation, without inducing disease. Although others had previously inoculated subjects with cowpox, Jenner was the first to show that the procedure induced immunity to smallpox. He later successfully popularised cowpox vaccination.
Jenner is often called "the father of immunology", and his work is said to have "saved more lives than the work of any other man".
March 1990: Proposal for a database of all viruses, later the ICTVdB
3 March 2014: Discovery of Pithovirus sibericum, the largest known virus at 1.5 μm long by 0.5 μm in diameter
4 March 1918: First case reported in the 1918 influenza pandemic
10 March 1956: Francis Crick and James Watson proposed that small viruses have a protein shell consisting of a large number of identical subunits
10 March 1956: Donald Caspar published paper on the structure of tomato bushy stunt virus
13 March 2003: Enfuvirtide (T20) approved; first HIV fusion inhibitor, also first HIV entry inhibitor
20 March 1987: Antiretroviral drug AZT (pictured) became the first antiviral medication approved for use against HIV/AIDS
22 March 2014: First case reported in the West African Ebola outbreak, the most widespread so far
26 March 1953: Jonas Salk reported a successful test of an inactivated polio vaccine.
28 March 2003: Mimivirus shown to be a virus, then the largest known
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Zidovudine (ZDV) (also known as AZT and Retrovir) is an antiretroviral drug used in the treatment of HIV/AIDS. Classed as a nucleoside analogue reverse-transcriptase inhibitor, it inhibits HIV's reverse transcriptase enzyme, which copies the viral RNA into DNA and is essential for its replication. The first breakthrough in AIDS therapy, ZDV was licensed in 1987. While it significantly reduces HIV replication, leading to clinical and immunological benefits, when used alone ZDV does not completely stop replication, allowing the virus to become resistant to it. The drug is therefore used together with other anti-HIV drugs in combination therapy called highly active antiretroviral therapy (HAART). To simplify its administration, ZDV is included in Combivir, Trizivir and other combination pills. ZDV can also be used to prevent HIV transmission, such as from mother to child during childbirth or after a needlestick injury.
A selection of recent articles of interest include:
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