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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/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
Influenza, or flu, is an infectious disease caused by some orthomyxoviruses, that affects birds and some mammals including humans, horses and pigs. Influenza is predominantly transmitted through the air by coughs. Or sneezes, creating aerosols containing the virus. It can also be transmitted by contact with bird droppings or nasal secretions, or by touching contaminated surfaces. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection. Around a third of cases show no symptoms. The most common symptoms include fever, runny nose, sore throat, muscle pains, headache, cough and fatigue. Influenza is occasionally associated with nausea and vomiting, particularly in children. Pneumonia is a rare complication which can be life-threatening.
Influenza spreads around the world in seasonal epidemics, resulting in about 3–5 million cases of severe illness annually, and about 250,000–500,000 deaths, mainly in the young, the old and those with other health problems. Annual influenza vaccinations are recommended for those at high risk. Sporadic influenza pandemics have been recorded since at least the 16th century. The Spanish flu pandemic of 1918–20 is estimated to have killed 50–100 million people.
Selected image
CCR5 is a human membrane protein that acts as a secondary receptor for HIV, enabling the viral and cell membranes to fuse. People with two copies of a mutated Δ32 form of CCR5 are naturally resistant to infection by most strains of HIV, and the normal form is the target of entry inhibitors such as maraviroc.
Credit: Thomas Splettstoesser (18 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
Interferons are a group of signalling proteins released by host cells in response to viruses and other pathogens. They belong to a large class of proteins known as cytokines: molecules used for communication between cells to trigger the protective defences of the immune system that help to eradicate pathogens. More than twenty distinct interferon genes and proteins have been identified in animals, including humans.
When a cell is infected by a virus, several virus products, including glycoproteins and viral RNA, stimulate the cell to produce and release interferons. This causes nearby cells to heighten their defences against viral infection, and so interferes with viral replication. Some viruses, including Japanese encephalitis virus, dengue type 2 virus, human cytomegalovirus and Kaposi's sarcoma-associated herpesvirus, have evolved ways to resist interferon's antiviral activity. Interferons also have various other functions in regulating the immune system. Interferons and other cytokines are responsible for some symptoms of infection, such as fever, muscle pain and "flu-like symptoms".
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 ÂŁ8 billion in the UK.
Selected quotation
| “ | Viruses are living chemicals... | ” |
—Alison Jolly
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
Alphaviruses are a genus of RNA viruses in the Togaviridae family. The spherical enveloped virion is 70 nm in diameter, with a nucleocapsid of 40 nm. It has a single-stranded, positive-sense RNA genome of 11–12 kb. The genus contains more than thirty species, which infect humans, horses, rodents and other mammals, as well as fish, birds, other vertebrates and invertebrates. Alphaviruses are generally transmitted by insect vectors, predominantly mosquitoes, and are an example of arboviruses (arthropod-borne viruses).
The first alphavirus to be discovered was western equine encephalitis virus, by Karl Friedrich Meyer in 1930, in horses with fatal encephalitis in San Joaquin Valley, California, USA. Some members of the genus cause significant disease in humans, including the chikungunya, o'nyong'nyong, Ross River, Sindbis, Barmah Forest and Semliki Forest (pictured) viruses and the eastern, western and Venezuelan equine encephalitis viruses. Arthritis, encephalitis, rashes and fever are the most frequently observed symptoms. Large mammals such as humans usually form dead-end hosts for the viruses, although Venezuelan equine encephalitis virus is mainly amplified in the horse. No human vaccine or antiviral drug has been licensed. Prevention is predominantly by control of the insect vector.
Did you know?
- ...that the groundnut rosette virus, which causes serious damage to peanut crops in Africa (plant pictured), is spread by the groundnut aphid?
- ...that Oguntola Sapara infiltrated and exposed a secret society in Nigeria that was deliberately spreading smallpox?
- ...that with the 2008 bird flu outbreak in West Bengal, 16,000 birds were destroyed in Itahar, but health workers retreated from villages that refused to kill their birds?
- ...that Preparing for Emergencies was a British Home Office programme to increase public safety after several major disasters, including the Madrid bombings, SARS outbreak and UK foot and mouth crisis?
- ...that Sounds of HIV sets the genome of the HIV/AIDS virus to music?
Selected biography
Jonas Edward Salk (28 October 1914 – 23 June 1995) was an American medical researcher and virologist, best known for developing the first successful polio vaccine.
Unlike most other researchers, Salk focused on creating an inactivated or "killed" virus vaccine, for safety reasons. The vaccine he developed combines three strains of wild-type poliovirus, inactivated with formalin. The field trial that tested its safety and efficacy in 1954 was one of the largest carried out to date, with vaccine being administered to over 440,000 children. When the trial's success was announced, Salk was hailed as a miracle worker and national hero. A little over two years later, 100 million doses of the vaccine had been distributed throughout the US, with few reported adverse effects. An inactivated vaccine based on the Salk vaccine is the mainstay of polio control in many developed countries.
Salk also researched vaccines against influenza and HIV. In 1960, he founded the Salk Institute for Biological Studies research centre in La Jolla, California.
In this month
1 July 1796: Edward Jenner first challenged James Phipps with variolation, showing that cowpox inoculation is protective against smallpox
3 July 1980: Structure of southern bean mosaic virus solved by Michael Rossmann and colleagues
6 July 1885: Louis Pasteur (pictured) gave rabies vaccine to Joseph Meister
10 July 1797: Jenner submitted paper on Phipps and other cases to the Royal Society; it was read to the society but not published
14–20 July 1968: First International Congress for Virology held in Helsinki
16 July 2012: FDA approved tenofovir/emtricitabine (Truvada) for prophylactic use against HIV; first prophylactic antiretroviral
19 July 2013: Pandoravirus described, with a genome twice as large as Megavirus
22 July 1966: International Committee on Nomenclature of Viruses (later the ICTV) founded
25 July 1985: Film star Rock Hudson made his AIDS diagnosis public, increasing public awareness of the disease
28 July 2010: First global World Hepatitis Day
Selected intervention
Two polio vaccines are used against the paralytic disease polio. The first, developed by Jonas Salk, consists of inactivated poliovirus. Based on three wild virulent strains, inactivated using formalin, it is administered by injection and is very safe. It confers IgG-mediated immunity, which prevents poliovirus from entering the bloodstream and protects the motor neurons, eliminating the risk of bulbar polio and post-polio syndrome. The second, developed by Albert Sabin, originally consisted of three live virus strains, attenuated by growth in cell culture. Since 2016, only two strains have generally been included. They contain multiple mutations, preventing them from replicating in the nervous system. The Sabin vaccine stimulates both antibodies and cell-mediated immunity, providing longer-lasting immunity than the Salk vaccine. It can be administered orally, making it more suitable for mass vaccination campaigns. In around three cases per million doses, the live vaccine reverts to a virulent form and causes paralysis. Vaccination has reduced the number of wild-type polio cases from around 350,000 in 1988 to just 33 in 2018, and eradicated the disease from most countries.
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