The Viruses Portal
Welcome!
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 6,000 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".
Selected disease
Dengue fever, or breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles. Rarely, the disease develops into the life-threatening dengue haemorrhagic fever, resulting in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs.
Dengue is transmitted by several species of Aedes mosquito, mainly A. aegypti. First described in 1779, the incidence of dengue fever has increased dramatically since the Second World War, with around 390 million people infected each year, of whom about 40,000 die. The virus is endemic in more than 120 countries, mainly in Southeast Asia, South Asia and South America. Infection with one of the five viral types usually gives lifelong immunity to that type but only short-term immunity to the others, and subsequent infection with a different type increases the risk of severe complications. Treatment of acute dengue is supportive, using oral or intravenous fluids for mild or moderate disease; blood transfusion may be required in more severe cases. A vaccine against dengue fever is available. Reducing mosquito habitats and limiting exposure to bites are the other main methods of control.
Selected image
Tobacco mosaic virus was the first virus to be identified, as an infectious agent that could pass through porcelain filters, as well as the first to be crystallised. It was among the earliest virus structures to be modelled successfully.
Credit: Thomas Splettstoesser (20 July 2012)
In the news
26 February: In the ongoing pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 110 million confirmed cases, including 2.5 million deaths, have been documented globally since the outbreak began in December 2019. WHO
18 February: Seven asymptomatic cases of avian influenza A subtype H5N8, the first documented H5N8 cases in humans, are reported in Astrakhan Oblast, Russia, after more than 100,0000 hens died on a poultry farm in December. WHO
14 February: Seven cases of Ebola virus disease are reported in Gouécké, south-east Guinea. WHO
7 February: A case of Ebola virus disease is detected in North Kivu Province of the Democratic Republic of the Congo. WHO
4 February: An outbreak of Rift Valley fever is ongoing in Kenya, with 32 human cases, including 11 deaths, since the outbreak started in November. WHO
21 November: The US Food and Drug Administration (FDA) gives emergency-use authorisation to casirivimab/imdevimab, a combination monoclonal antibody (mAb) therapy for non-hospitalised people twelve years and over with mild-to-moderate COVID-19, after granting emergency-use authorisation to the single mAb bamlanivimab earlier in the month. FDA 1, 2
18 November: The outbreak of Ebola virus disease in Équateur Province, Democratic Republic of the Congo, which started in June, has been declared over; a total of 130 cases were recorded, with 55 deaths. UN
Selected article
.jpg)
Bats host a diverse array of viruses, including all seven types described by the Baltimore classification system. The most common viruses known to infect bats are coronaviruses. Bats harbour many viruses that are zoonotic, or capable of infecting humans, including rabies virus, SARS-CoV, SARS-CoV-2, MERS-CoV, Nipah virus, Hendra virus and Marburg virus (hosted by the Egyptian fruit bat; pictured), and some bat-borne viruses are considered important emerging viruses. Bats may also play a role in the ecology of the Ebola virus. Most zoonotic bat viruses are transmitted by direct contact with infected bat fluids such as urine, guano and saliva, or through contact with an infected intermediate host; transmission of rabies from bats to humans usually occurs via biting. Butchering or consuming bat meat could potentially lead to viral transmission.
Bats rarely become ill from viral infections, and rabies is the only viral disease known to kill them. They might be more tolerant of infection than other mammals. Their immune systems differ from those of other mammals in their lack of several inflammasomes, which activate the body's inflammatory response, as well as a dampened stimulator of interferon genes response, which helps to control the host response to pathogens.
Selected outbreak
The 1918–20 influenza pandemic, the first of the two involving H1N1 influenza virus, was unusually deadly. 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 has also been implicated in the outbreak of encephalitis lethargica in the 1920s. Despite the nickname "Spanish flu", the pandemic's geographic origin is unknown.
Most influenza outbreaks disproportionately kill young, elderly or already weakened patients; in contrast this predominantly killed healthy young adults. Contemporary medical reports suggest that malnourishment, overcrowded medical facilities and poor hygiene promoted fatal bacterial pneumonia. Some research suggests that the virus might have killed through a cytokine storm, an overreaction of the body's immune system. This would mean the strong immune reactions of young adults resulted in a more severe disease than the weaker immune systems of children and older adults.
Selected quotation
| “ | There are more viruses on Earth than stars in the universe. | ” |
Recommended articles
Viruses & Subviral agents: bat virome • elephant endotheliotropic herpesvirus • HIV • introduction to viruses
• Playa de Oro virus • poliovirus • prion • rotavirus • virus
Diseases: colony collapse disorder • common cold • croup • dengue fever • gastroenteritis • Guillain–Barré syndrome • hepatitis B • hepatitis C • hepatitis E • herpes simplex • HIV/AIDS • influenza • meningitis • myxomatosis • polio • pneumonia • shingles • smallpox
Epidemiology & Interventions: 2007 Bernard Matthews H5N1 outbreak • Coalition for Epidemic Preparedness Innovations • Disease X • 2009 flu pandemic • HIV/AIDS in Malawi • polio vaccine • Spanish flu • West African Ebola virus epidemic
Virus–Host interactions: antibody • host • immune system • parasitism • RNA interference
Methodology: metagenomics
Social & Media: And the Band Played On • Contagion • "Flu Season" • Frank's Cock • Race Against Time: Searching for Hope in AIDS-Ravaged Africa • social history of viruses • "Steve Burdick" • "The Time Is Now" • "What Lies Below"
People: Brownie Mary • Macfarlane Burnet • Bobbi Campbell • Aniru Conteh • people with hepatitis C • HIV-positive people • Bette Korber • Henrietta Lacks • Linda Laubenstein • Barbara McClintock • poliomyelitis survivors • Joseph Sonnabend • Eli Todd • Ryan White
Selected virus
Adeno-associated viruses (AAVs) are two small DNA viruses in the Dependoparvovirus genus of the Parvoviridae family. They cannot complete their lytic replication cycle without a helper virus, which include adenoviruses, herpesviruses and vaccinia. In the absence of the helper, AAVs can integrate into the host genome at a specific site on human chromosome 19, or persist as an episome. The 20 nm icosahedral capsid lacks an envelope, and contains a single-stranded DNA genome of around 4.7 kb. AAVs infect humans and some other primates without causing disease. They generate only a mild immune response, including neutralising antibodies. The best-studied of the 11 serotypes, AAV-2, infects nerve cells, liver cells, skeletal muscle and vascular smooth muscle, using heparan sulphate proteoglycan as its primary receptor.
Its low pathogenicity makes AAV an attractive basis for viral vectors for gene therapy. Alipogene tiparvovec to treat lipoprotein lipase deficiency was the first gene therapy to be licensed, but was later withdrawn. Promising results have been obtained in early clinical trials with AAV-based gene therapy in haemophilia, congestive heart failure, spinal muscular atrophy, Parkinson's disease and the rare eye disease Leber congenital amaurosis.
Did you know?
.jpg)
- ...that a novel virus may be implicated in its parasitic wasp host turning the spotted lady beetle into a "zombie bodyguard" (pictured)?
- ...that the human immunodeficiency virus reappeared in the Mississippi baby after she was thought to be cured?
- ...that as of April 2014, the rose rosette virus had killed at least two-thirds of the roses in the Tulsa Rose Garden?
- ...that Virology is the first English-language journal to focus on viruses?
- ...that, after "Stop...pooping!" was uttered by Rob Lowe in the Parks and Recreation episode "Flu Season", the line was deemed the "single greatest self-effacingly comic moment of his long, handsome career"?
Selected biography
Many well-known people have survived the paralytic disease polio. The earliest identified case might be Siptah (pictured), Egyptian pharaoh 1197–1191 BC, whose mummified remains have a deformed leg possibly from polio. Claudius, Roman emperor 41–54 AD, walked with a limp after a childhood disease that historians have hypothesised might have been polio. Novelist Sir Walter Scott suffered paralysis in one leg after a teething fever in 1773, which left him lame; his detailed account of his disease has allowed a retrospective diagnosis of polio to be made with confidence.
For many of those who survived it, paralytic polio was a life-changing experience. The disease can lead to permanent physical disability; Itzhak Perlman, for example, plays the violin seated. Others recover completely, with some going on to excel in sports; Ray Ewry became world's foremost standing jumper after childhood polio. Some survivors, including singer Ian Dury and actress Mia Farrow, have campaigned for polio eradication or for disability rights.
In this month
7 November 1991: Magic Johnson announced his retirement from basketball because of his infection with HIV
14 November 1957: Kuru, the first human prion disease, described by Daniel Gajdusek and Vincent Zigas
16 November 2002: The first case of severe acute respiratory syndrome (virus pictured) recorded in Guangdong, China
17 November 1995: Lamivudine approved for treatment of HIV
22 November 2013: Simeprevir approved for treatment of chronic hepatitis C virus infection
23 November 1978: Structure of tomato bushy stunt virus solved by Stephen Harrison and colleagues, the first atomic-level structure of a virus
24 November 2007: Outbreak of new Ebola species, Bundibugyo virus
26 November 1898: Martinus Beijerinck coined the term contagium vivum fluidum to describe the agent causing tobacco mosaic disease
Selected intervention
.jpg)
Influenza vaccines include live attenuated and inactivated forms. Inactivated vaccines contain three or four different viral strains selected by the World Health Organization to cover influenza A H1N1 and H3N2, as well as influenza B, and are usually administered by intramuscular injection. The live attenuated influenza vaccine contains a cold-adapted strain and is given as a nasal spray. Most influenza vaccine strains are cultivated in fertilised chicken eggs (pictured), a technique developed in the 1950s; others are grown in cell cultures, and some vaccines contain recombinant proteins. Annual vaccination is recommended for high-risk groups and, in some countries, for all those over six months. As the influenza virus changes rapidly by antigenic drift, new versions of the vaccine are developed twice a year, which differ in effectiveness depending on how well they match the circulating strains. Despite considerable research effort for decades, no effective universal influenza vaccine has been identified. A 2018 meta-analysis found that vaccination in healthy adults decreased confirmed cases of influenza from about 2.4% to 1.1%. However, the effectiveness is uncertain in those over 65 years old, one of the groups at highest risk of serious complications.
Subcategories
Subcategories of virology:
Topics
Things to do
- Comment on what you like and dislike about this portal
- Join the Viruses WikiProject
- Tag articles on viruses and virology with the project banner by adding {{WikiProject Viruses}} to the talk page
- Assess unassessed articles against the project standards
- Create requested pages: red-linked viruses | red-linked virus genera
- Expand a virus stub into a full article, adding images, citations, references and taxoboxes, following the project guidelines
- Create a new article (or expand an old one 5-fold) and nominate it for the main page Did You Know? section
- Improve a B-class article and nominate it for Good Article
or Featured Article
status - Suggest articles, pictures, interesting facts, events and news to be featured here on the portal
WikiProjects & Portals
WikiProject Viruses
Related WikiProjects
Medicine • Microbiology • Molecular & Cellular Biology • Veterinary Medicine
Related Portals
.svg){kind=small}
Associated Wikimedia
The following Wikimedia Foundation sister projects provide more on this subject:
-
Commons
Free media repository -
Wikibooks
Free textbooks and manuals -
Wikidata
Free knowledge base -
Wikinews
Free-content news -
Wikiquote
Collection of quotations -
Wikisource
Free-content library -
Wikispecies
Directory of species -
Wikiversity
Free learning tools -
Wiktionary
Dictionary and thesaurus
