Portal:Viruses
The Viruses Portal
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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
Foot-and-mouth disease or FMD is an economically important disease of even-toed ungulates (cloven-hoofed animals) and some other mammals caused by the FMD virus, a picornavirus. Hosts include cattle, water buffalo, sheep, goats, pigs, antelope, deer and bison; human infection is extremely rare. After a 1–12-day incubation, animals develop high fever, and then blisters inside the mouth (pictured) and on the hooves, which can rupture and cause lameness. Weight loss and reduction in milk production are other possible long-term consequences. Mortality in adult animals is low (2–5%). The virus is highly infectious, with transmission occurring via direct contact, aerosols, semen, consumption of infected food scraps or feed supplements, and via inanimate objects including fodder, farming equipment, vehicles, standing water, and the clothes and skin of humans. Some infected ruminants can transmit infection as asymptomatic carriers.
Friedrich Loeffler showed the disease to be viral in 1897. FMD was widely distributed in 1945. By 2014, North America, Australia, New Zealand, much of Europe, and some South American countries were free of the disease. Major outbreaks include one in the UK in 2001 that cost an estimated £8 billion. The virus is highly variable, with seven serotypes. A vaccine is available, but protection is temporary and strain specific. Other control methods include monitoring programmes, trade restrictions, quarantine, and the slaughter of infected and healthy at-risk animals.
Selected image
Many small icosahedral viruses have capsids made up of multiple copies of just two proteins. The proteins aggregate into units called capsomeres, which have either pentagonal or hexagonal symmetry (as shown here).
Credit: Antares42 (4 September 2009)
In the news
27 November: In the ongoing pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 60 million confirmed cases, including more than 1.4 million deaths, have been documented globally since the outbreak began in December 2019. 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
16 November: Interim unpublished results from an ongoing Phase III trial in around 30,000 participants suggest that an mRNA vaccine from Moderna targeting the SARS-CoV-2 S glycoprotein is at least 94% effective at preventing COVID-19 disease after two doses. Nature
9 November: Interim unpublished results from an ongoing Phase III trial in 43,538 participants suggest that an mRNA vaccine from Pfizer/BioNTech targeting the SARS-CoV-2 S glycoprotein is at least 90% effective at preventing COVID-19 disease after two doses. Nature
5 November: A cluster of COVID-19 cases associated with mink farming, in which the causative SARS-CoV-2 strain harbours a novel combination of mutations and appears less susceptible to neutralising antibodies, are reported from North Jutland, Denmark; the news triggers the slaughter of all farmed mink across the country. WHO
29 October: The Howard Hughes Medical Institute announces a donation to the Henrietta Lacks Foundation, intended as reparation for the harvesting of cervical cancer cells from Lacks in 1951, without her consent; the cells were subsequently used to create the HeLa cell line. Nature
22 October: The US FDA approves the repurposed antiviral remdesivir for the treatment of SARS-CoV-2 infection; the decision has been criticised owing to the drug's apparent lack of benefit in as-yet-unpublished interim results from the World Health Organization's (WHO) Solidarity trial. Science
14 October: A combination of three monoclonal antibodies, atoltivimab, maftivimab and odesivimab-ebgn, is licensed by the US FDA as the first treatment for Ebola virus disease. FDA
25 August: Africa is declared free from wild poliovirus, with the last case having been detected in Nigeria in 2016; vaccine-derived polio cases continue to be recorded in the region. Nature
20 August: The International Committee on Taxonomy of Viruses creates three new realms for DNA viruses – Duplodnaviria, for double-stranded DNA (dsDNA) viruses with HK97-fold capsid proteins, including tailed bacteriophages and herpesviruses; Varidnaviria for dsDNA viruses with jelly-roll capsid proteins, such as adenoviruses and poxviruses; and Monodnaviria for most single-stranded DNA viruses, including papillomaviruses – and also extends Riboviria to include RNA viruses that replicate using reverse transcriptase. ICTV
Selected article
Vaccination or immunisation is the administration of immunogenic material (a vaccine) to stimulate an individual's immune system to develop adaptive immunity to a virus or other pathogen, and so develop protection against an infectious disease. The active agent of a vaccine may be intact but inactivated or weakened forms of the pathogen, or purified highly immunogenic components, such as viral envelope proteins. Smallpox was the first disease for which a vaccine was produced, by Edward Jenner in 1796.
Vaccination is the most effective method of preventing infectious diseases and can also ameliorate the symptoms of infection. When a sufficiently high proportion of a population has been vaccinated, herd immunity results. Widespread immunity due to mass vaccination is largely responsible for the worldwide eradication of smallpox and the elimination of diseases such as polio from much of the world. Since their inception, vaccination efforts have met with objections on scientific, ethical, political, medical safety and religious grounds, and the World Health Organization considers vaccine hesitancy an important threat to global health.
Selected outbreak
The 2009 flu pandemic was an influenza pandemic first recognised in Mexico City in March 2009 and declared over in August 2010. It involved a novel strain of H1N1 influenza virus with genes from five different viruses, which resulted when a previous triple reassortment of avian, swine and human influenza viruses further combined with a Eurasian swine influenza virus, leading to the term "swine flu" being used for the pandemic. It was the second pandemic to involve an H1N1 strain, the first being the 1918 "Spanish flu" pandemic.
The global infection rate was estimated as 11–21%. This pandemic strain was less lethal than previous ones, killing about 0.01–0.03% of those infected, compared with 2–3% for Spanish flu. Most experts agree that at least 284,500 people died, mainly in Africa and Southeast Asia – comparable with the normal seasonal influenza fatalities of 290,000–650,000 – leading to claims that the World Health Organization had exaggerated the danger.
Selected quotation
| “ | ...classical approaches to classification are not suitable for viruses, as rigid hierarchies cannot be imposed on organisms that appear – evolutionarily speaking – to have been rather promiscuous in sharing their characteristics around. | ” |
—Ed Rybicki
Selected virus
Henipaviruses are a genus of RNA viruses in the Paramyxoviridae family. The variably shaped, 40–600 nm diameter, enveloped capsid contains a single-stranded, negative-sense RNA genome of 18.2 kb, with six genes. The cellular receptor is Ephrin B2. Their natural hosts are bats, mainly the Pteropus genus of megabats (flying foxes) and some microbats. Bats infected with Hendra virus develop viraemia and shed virus in urine, faeces and saliva for around a week, but show no signs of disease. Henipaviruses can also infect humans and livestock, causing severe disease with high mortality, making the group a zoonootic disease. Transmission to humans appears to occur via an intermediate domestic animal host.
The first henipavirus, Hendra virus, was discovered in 1994 as the cause of an outbreak in horses in Brisbane, Australia. Nipah virus was identified a few years later in Malaysia as the cause of an outbreak in pigs. Three other species have since been recognised. Their emergence as human pathogens has been linked to increased contact between bats and humans. Human disease has been confined to Australia and Asia, but members of the genus have also been found in African bats. A veterinary vaccine against Hendra virus is available but no human vaccine has been licensed.
Did you know?
- ...that extracts of pringamoza (pictured) have shown antiviral activity against herpes simplex?
- ...that structural biologist Erica Ollmann Saphire travelled to Africa to observe rodents in the field in order to study how viruses like Ebola are spread?
- ...that workplace hazard controls for COVID-19 include measures for psychosocial hazards such as stress and anxiety, for which social distancing may prevent typical coping mechanisms?
- ...that in 2011, Stephen J. Challacombe and colleagues laid out research challenges of global health inequalities and oral health, relating to TB, STDs, HIV, and Noma?
- ...that the 1957–1958 influenza pandemic killed at least one million people worldwide?
Selected biography
Françoise Barré-Sinoussi (born 30 July 1947) is a French virologist, known for being one of the researchers who discovered HIV.
Barré-Sinoussi researched retroviruses in Luc Montagnier's group at the Institut Pasteur in Paris. In 1982, she and her co-workers started to analyse samples from people with a new disease, then referred to as "gay-related immune deficiency". They found a novel retrovirus in lymph node tissue, which they called "lymphadenopathy-associated virus". Their results were published simultaneously with those of Robert Gallo's group in the USA, who had independently discovered the virus under the name "human T-lymphotropic virus type III". The virus, renamed "human immunodeficiency virus", was later shown to cause AIDS. Barré-Sinoussi continued to research HIV until her retirement in 2015, studying how the virus is transmitted from mother to child, the immune response to HIV, and how a small proportion of infected individuals, termed "long-term nonprogressors", can limit HIV replication without treatment. In 2008, she was awarded the Nobel Prize, with Montagnier, for the discovery of HIV.
In this month
1 January 1934: Discovery of mumps virus by Claud Johnson and Ernest Goodpasture
1 January 1942: Publication of George Hirst's paper on the haemagglutination assay
1 January 1967: Start of WHO intensified eradication campaign for smallpox (vaccination kit pictured)
3 January 1938: Foundation of March of Dimes, to raise money for polio
6 January 2011: Andrew Wakefield's paper linking the MMR vaccine with autism described as "fraudulent" by the BMJ
25 January 1988: Foundation of the International AIDS Society
29 January 1981: Influenza haemagglutinin structure published by Ian Wilson, John Skehel and Don Wiley, the first viral membrane protein whose structure was solved
Selected intervention
| “ | the most damaging medical hoax of the last 100 years —Dennis Flaherty, 2011 |
” |
The MMR vaccine and autism fraud refers to the false claim that the combined vaccine for measles, mumps and rubella (MMR) might be associated with colitis and autism spectrum disorders. Multiple large epidemiological studies have since found no link between the vaccine and autism. The notion originated in a fraudulent research paper by Andrew Wakefield and co-authors, published in the prestigious medical journal The Lancet in 1998. Sunday Times journalist Brian Deer's investigations revealed that Wakefield had manipulated evidence and had multiple undeclared conflicts of interest. The paper was retracted in 2010, when the Lancet's editor-in-chief Richard Horton characterised it as "utterly false". Wakefield was found guilty of serious professional misconduct by the General Medical Council, and struck off the UK's Medical Register. The claims in Wakefield's article were widely reported in the press, resulting in a sharp drop in vaccination uptake in the UK and Ireland. A greatly increased incidence of measles and mumps followed, leading to deaths and serious permanent injuries.
Subcategories
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
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