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
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Myxomatosis is a disease of rabbits caused by Myxoma virus, a poxvirus in the genus Leporipoxvirus. The natural hosts are brush rabbits (Sylvilagus bachmani) in North America and tapeti (S. brasiliensis) in South and Central America, in which the myxoma virus causes only a mild disease, involving skin nodules. In European rabbits (Oryctolagus cuniculus), it causes a severe, often fatal, disease. Symptoms include fever, swelling of the eyelids and anogenital area, a mucopurulent ocular and nasal discharge, respiratory distress and hypothermia. Death generally occurs 10–12 days after infection. Myxoma virus is transmitted passively (without replication) by arthropod vectors, usually via the bites of mosquitoes and fleas, and also mites, flies and lice. It can also be transmitted by direct contact, and is shed in the ocular and nasal discharge and from eroded skin.
Myxoma virus was intentionally introduced in Australia, France and Chile in the 1950s to control wild European rabbit populations. This resulted in short-term 10–100-fold reductions in the rabbit population, followed by its recovery with the emergence of myxomatosis-resistant animals and attenuated virus variants. The introduction of myxomatosis is regarded as a classical example of host–pathogen coevolution following cross-species transmission of a pathogen to a naive host.
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The striping caused by tulip breaking virus, first described in 1576 by Carolus Clusius, was the second plant virus disease to be documented. The effects were much prized by 17th-century tulip growers.
Credit: Unknown (before 1640)
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
Viruses and viral infections have affected human history. Epidemics caused by viruses began when human behaviour changed during the Neolithic period, around 12,000 years ago. Previously hunter-gatherers, humans developed more densely populated agricultural communities, which allowed viruses to spread rapidly and subsequently to become endemic. Viruses of plants and livestock also increased, and as humans became dependent on agriculture and farming, diseases such as potyviruses of potatoes and rinderpest of cattle had devastating consequences. Smallpox and measles viruses are among the oldest that infect humans. They first appeared in humans in Europe and North Africa thousands of years ago, having evolved from viruses that infected other animals. Influenza pandemics have been recorded since 1580.
There are an estimated 1031 viruses on Earth. Although scientific interest in them arose because of the diseases they cause, most viruses are beneficial. They drive evolution by transferring genes across species, play important roles in ecosystems, and are essential to life.
Selected outbreak
The 2001 foot-and-mouth outbreak included 2,000 cases of the disease in cattle and sheep across the UK. The source was a Northumberland farm where pigs had been fed infected meat that had not been adequately sterilised. The initial cases were reported in February. The disease was concentrated in western and northern England, southern Scotland and Wales, with Cumbria being the worst-affected area. A small outbreak occurred in the Netherlands, and there were a few cases elsewhere in Europe.
The UK outbreak was controlled by the beginning of October. Control measures included stopping livestock movement and slaughtering over 6 million cows and sheep. Public access to farmland and moorland was also restricted (pictured), greatly reducing tourism in affected areas, particularly in the Lake District. Vaccination was used in the Netherlands, but not in the UK due to concerns that vaccinated livestock could not be exported. The outbreak cost an estimated £8 billion in the UK.
Selected quotation
| “ | ...getting rid of the last 1 percent has been like trying to squeeze Jell-O to death. As the vaccination fist closes in one country, the virus bursts out in another... | ” |
—Donald McNeil on the campaign to eradicate polio
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
Hepatitis delta virus or hepatitis D virus (HDV) is a small virusoid, the sole member of the Deltavirus genus. It infects humans. A subviral satellite, it can only replicate in the presence of a hepatitis B (HBV) helper virus. The spherical virion is 36 nm in diameter, with an envelope containing three HBV proteins. The single-stranded, negative-sense, circular RNA genome of 1679 nucleotides is smaller than that of any known animal virus. It has an unusual base composition for an entity that infects animals, and is extensively bound to itself to form a partially double-stranded, rod-shaped structure. These features have led to suggestions that HDV might be related to viroids, small unencapsidated circular RNAs that infect plants. Unlike viroids, HDV encodes a protein, hepatitis D antigen.
Both HDV and HBV enter liver cells using the sodium/bile acid cotransporter as their receptor. They are mainly transmitted via injecting drug use and blood products. More than 15 million people are infected with both viruses, which is associated with a greater risk of liver complications than HBV infection alone. Around one in five jointly infected patients die. The HBV vaccine protects against HDV.
Did you know?
- ...that Burchard Kranich allegedly cured Queen Elizabeth I (pictured) of smallpox?
- ...that the rabbit flea is a vector for the virus that causes myxomatosis?
- ...that when NBC pulled "Steve Burdick", an AIDS-themed episode of the medical drama Lifestories, gay and AIDS activists accused the network of fearing advertiser backlash?
- ...that in addition to infecting squashes, the squash mosaic virus also infects melons?
- ...that former GlaxoSmithKline executive Moncef Slaoui is chief adviser to Operation Warp Speed, which aims to deliver 300 million doses of a vaccine for COVID-19 by January 2021?
Selected biography
George Keble Hirst (2 March 1909 – 22 January 1994) was an American virologist who was among the first to study the molecular biology and genetics of animal viruses.
Hirst started to work on influenza virus in 1940, only a few years after it had been isolated. He soon discovered that the virus caused red blood cells to clump together. This phenomenon could be used to diagnose influenza, which had previously required growing the virus in ferrets. He invented the haemagglutination assay, a simple method for quantifying viruses, and later the haemagglutination inhibition assay, which measures virus-specific antibodies in serum. In 1942, he discovered the neuraminadase enzyme, showing for the first time that viruses could contain enzymes. Neuraminidase is the target of the neuraminidase inhibitor class of antiviral drugs, including oseltamivir and zanamivir. In 1962, he was also the first to propose the then-revolutionary idea that virus genomes can consist of discontinuous segments.
He co-founded Virology in 1955, the first English-language journal to focus on viruses, and directed the Public Health Research Institute in New York City for nearly 25 years (1956–81).
In this month
May 1955: First issue of Virology; first English-language journal dedicated to virology
4 May 1984: HTLV-III, later HIV, identified as the cause of AIDS by Robert Gallo and coworkers
5 May 1939: First electron micrographs of tobacco mosaic virus taken by Helmut Ruska and coworkers
5 May 1983: Structure of influenza neuraminidase solved by Jose Varghese, Graeme Laver and Peter Colman
8 May 1980: WHO announced formally the global eradication of smallpox
11 May 1978: SV40 sequenced by Walter Fiers and coworkers
12 May 1972: Gene for bacteriophage MS2 coat protein is sequenced by Walter Fiers and coworkers, the first gene to be completely sequenced
13 May 2011: Boceprevir approved for the treatment of chronic hepatitis C virus (HCV) infection, the first direct-acting antiviral for HCV
14 May 1796: Edward Jenner inoculated James Phipps (pictured) with cowpox
15/16 May 1969: Death of Robert Rayford, the earliest confirmed case of AIDS outside Africa
18 May 1998: First World AIDS Vaccine Day
20 May 1983: Isolation of the retrovirus LAV, later HIV, by Luc Montagnier, Françoise Barré-Sinoussi and coworkers
23 May 2011: Telaprevir approved for the treatment of chronic HCV infection
25 May 2011: WHO declared rinderpest eradicated
31 May 1937: First results in humans from the 17D vaccine for yellow fever published by Max Theiler and Hugh H. Smith
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.
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