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
AIDS is a progressive immunodeficiency disease first recognised in 1981, caused by infection with human immunodeficiency virus (HIV). Initial infection is sometimes associated with a brief influenza-like illness, followed by a period of 3–20 years without symptoms during which the immune system deteriorates. The individual becomes highly susceptible to common infections such as tuberculosis, as well as opportunistic infections, such as Pneumocystis pneumonia, and tumours, such as Kaposi's sarcoma and lymphoma. Severe weight loss is also a feature of AIDS. Without treatment, the average survival time after infection is around 9–11 years, depending on the HIV subtype.
HIV/AIDS is a global pandemic. As of 2018, nearly 38 million people worldwide are estimated to be infected with HIV, with 1.8 million new infections occurring each year. AIDS has caused around 32 million deaths. The major routes of transmission are unsafe heterosexual or male/male sex, contaminated needles and blood transfusions, and from mother to child, either at birth or via breastfeeding. Combination antiretroviral therapy does not eliminate the virus, but delays progression to AIDS and can lead to a near-normal life expectancy. Drugs to prevent infection are now available, but there is no effective HIV vaccine.
Selected image
Ebola virus (coloured green), a filamentous RNA virus, budding from a chronically infected African green monkey kidney cell in culture.
Credit: BernbaumJG (28 August 2014)
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
Infectious diseases are symptomatic diseases of an individual host resulting from the infection and replication of pathogens, including viruses, prions, bacteria, fungi, protozoa and multicellular parasites. Infectious diseases were responsible for 17% of human deaths globally in 2013, with HIV, measles and influenza being among the most significant viral causes of death.
Infectious pathogens must enter, survive and multiply within the host, and spread to fresh hosts. Relatively few microorganisms cause disease in healthy individuals, and infectious disease results from the interplay between these rare pathogens and the host's defences. Infection does not usually result in the host's death. The pathogen is generally cleared from the body by the host's immune system, although persistent infection occurs with several viruses. Transmission can occur by physical contact, contaminated food, water or objects, body fluids, airborne inhalation or via vectors, such as the mosquito (pictured). Diagnosis sometimes involves identifying the pathogen; techniques include culture, microscopy, immunoassays and PCR-based diagnostics.
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
| “ | A virus is a piece of bad news wrapped in protein. | ” |
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
West Nile virus (WNV) is a flavivirus, an RNA virus in the Flaviviridae family. The enveloped virion is 45–50 nm in diameter and contains a single-stranded, positive-sense RNA genome of around 11,000 nucleotides, encoding ten proteins. The main natural hosts are birds (the reservoir) and several species of Culex mosquito (the vector). WNV can also infect humans and some other mammals, including horses, dogs and cats, as well as some reptiles. Transmission to humans is generally by bite of the female mosquito. Mammals form a dead end for the virus, as it cannot replicate sufficiently efficiently in them to complete the cycle back to the mosquito.
First identified in Uganda in 1937, WNV was at first mainly associated with disease in horses, with only sporadic cases of human disease until the 1990s. The virus is now endemic in Africa, west and central Asia, Oceania, the Middle East, Europe and North America. A fifth of humans infected experience West Nile fever, a flu-like disease. In less than 1% of those infected, the virus invades the central nervous system, causing encephalitis, meningitis or flaccid paralysis. No specific antiviral treatment has been licensed and only a veterinary vaccine is available. Mosquito control is the main preventive measure.
Did you know?
- ...that the genetically modified plum C5 is the only Prunus species resistant to the devastating plant disease plum pox?
- ...that research by Dorothy M. Horstmann and Robert W. McCollum at Yale University showed that the poliovirus reaches the brain by way of the blood, leading to the development of the polio vaccine in the early 1950s?
- ...that sea sponge aquaculture has the potential to generate novel anti-inflammatory and antiviral drugs?
- ...that in response to the Hong Kong government refusing to close its border with mainland China to contain COVID-19, Winnie Yu organized a labour strike among hospital workers in February 2020?
- ...that CCR5 receptor antagonists are drugs that inhibit the entry of HIV into cells of the immune system?
Selected biography
Edward Jenner (1749–1823) was an English physician and scientist who pioneered the smallpox vaccine, the world's first 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. In 1796, Jenner tested his hypothesis by inoculating an eight-year-old boy with pus from an infected milkmaid. He subsequently repeatedly challenged the boy with variolous material, then the standard method of immunisation, without inducing disease. He published a paper including 23 cases in 1798. Although several 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 that of any other individual.
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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