Portal:Viruses
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 5,000 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".
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Poliomyelitis, also called polio or infantile paralysis, was one of the most feared childhood diseases of the 20th century. It has caused paralysis and death for much of human history. The causative agent, poliovirus, spreads via the faecal–oral route. Infections are usually asymptomatic, but in about 1% of cases, the virus enters the central nervous system and preferentially infects and destroys motor neurons, leading to muscle weakness and acute flaccid paralysis. Spinal polio is the most common form, accounting for nearly 80% of cases of paralytic polio; it is characterized by asymmetric paralysis usually involving the legs. Bulbar involvement is rare, but in severe cases the virus can affect the phrenic nerve and prevent breathing, so that patients require mechanical ventilation with an iron lung or similar device.
Polio had existed for thousands of years as an endemic pathogen until the 1880s, when major epidemics began to occur in Europe and later the United States. Polio vaccines developed in the 1950s have reduced the annual incidence from many hundreds of thousands to under a thousand, and as of 2013, a global eradication campaign is ongoing.
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The antiviral fomivirsen was the first antisense therapy to be licensed by the FDA. It binds to a cytomegalovirus mRNA and is used to treat cytomegalovirus retinitis.
Credit: Fvasconcellos (1 January 2007)
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Infectious diseases are symptomatic diseases resulting from the infection and replication of pathogens, including viruses, prions, bacteria, fungi, protozoa and multicellular parasites, in an individual host. Infectious diseases were responsible for over a quarter of human deaths globally in 2002, 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, and the pathogen is generally cleared from the body by the host's immune system. Transmission can occur by physical contact, contaminated food, body fluids, objects, airborne inhalation or via vectors, such as the mosquito (pictured). Diagnosis often involves identifying the pathogen; techniques include culture, microscopy, immunoassays and PCR-based molecular diagnostics.
16 March: Multiple new cases of Ebola virus are reported in Koropara, southern Guinea. WHO
10 March: The ongoing Middle East respiratory syndrome coronavirus outbreak (virus pictured) continues in Saudi Arabia and Qatar, with 46 new cases in February and March. WHO
8 March: Endogenous retrovirus Fc sequences, first identified in primates, are found in 11 different mammalian orders including rodents and carnivores. eLife
4 March: Endogenous retrovirus regulatory elements act as enhancers for interferon-induced immune genes in mammals. Science
4 March: Abnormal foetal ultrasound results are found in 12 of 42 pregnant women infected with Zika virus in Rio de Janeiro. NEJM
4 March: Zika virus is shown to productively infect human neural progenitor cells in vitro, causing cell death. Cell Stem Cell
1 March: The first dengue outbreak in Uruguay is reported, with 17 confirmed cases, mainly in Montevideo. WHO
27 February: The first chikungunya outbreak (virus pictured) in Argentina is reported, with 30 confirmed non-imported cases, mainly in Tartagal. WHO
29 February: A case-control study in 42 people with Guillain–Barré syndrome in Tahiti, French Polynesia in 2013–14 suggests that Zika virus might cause the syndrome. Lancet
24 February: A meta-analysis estimates that 2.3 million people, mainly those who inject drugs, are infected with both HIV and hepatitis C virus (HCV) and 82% of HIV+ injecting drug users are also infected with HCV. Lancet Infect Dis
24 February: In 82 Liberian Ebola survivors participating in the PREVAIL III study, frequent neurological problems are seen at least 6 months after the onset of symptoms. EurekAlert
23 February: Japanese encephalitis virus can be transmitted directly between pigs, without requiring a mosquito vector. Nat Commun
17 February: A novel gammaherpesvirus related to equine herpesvirus 2 is discovered in a cell line derived from the cave myotis bat (pictured). mSphere
16 February: An outbreak of Lassa fever occurs in Benin, with 71 suspected cases including 23 deaths; a Nigerian outbreak is also ongoing. WHO 1, 2 Template:/box-footer
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The West African Ebola epidemic was the most widespread outbreak of the disease to date, and the first to occur outside Sub-Saharan Africa. Beginning in Meliandou in southern Guinea in December 2013, it spread to adjacent Liberia and Sierra Leone, affecting the densely populated cities of Conakry and Monrovia, with minor outbreaks in Mali and Nigeria. The epidemic was under control by late 2015, but occasional cases continue to occur as of March 2016. More than 28,000 suspected cases were reported with more than 11,000 deaths, a case fatality rate of around 58% in hospitalised patients and up to 70% overall. Around 10% of the dead were healthcare workers.
Extreme poverty, a dysfunctional healthcare system, a distrust of government officials after years of armed conflict, local burial customs involving washing the body after death, and a delay in response of several months all contributed to the failure to contain the epidemic.
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| “ | We are part virus. This bizarre yet inescapable fact has been revealed over the past 30 years, as scientists have spelunked their way through the human genome and encountered stretches of DNA with the telltale chemical signatures of viruses. | ” |
Template:/box-header Viruses & Subviral agents: elephant endotheliotropic herpesvirus • HIV • introduction to viruses
• Playa de Oro virus • poliovirus • prion • rotavirus • viruses
Diseases: colony collapse disorder • common cold • dengue fever • gastroenteritis • Guillain–Barré syndrome • hepatitis B • hepatitis C • herpes simplex • HIV/AIDS • influenza • meningitis • poliomyelitis • shingles • smallpox
Epidemiology & Interventions: 1918 flu pandemic • 2007 Bernard Matthews H5N1 outbreak • 2009 flu pandemic • HIV/AIDS in Malawi • polio vaccine
Host response: antibody • immune system • RNA interference
Social & Media: And the Band Played On • Contagion • "Flu Season" • Frank's Cock • Race Against Time • social history of viruses • "Steve Burdick" • "The Time Is Now"
People: Brownie Mary • Frank Macfarlane Burnet • Aniru Conteh • HIV-positive people • people with hepatitis C • poliomyelitis survivors • Ryan White Template:/box-footer
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Acanthamoeba polyphaga mimivirus (APMV) is the only species in the Mimivirus genus of the Mimiviridae family of DNA viruses. It infects the amoeba, Acanthamoeba polyphaga. Its non-enveloped icosahedral capsid is 400 nm in diameter, with protein filaments of 100 nm projecting from its surface. The APMV genome is a linear, double-stranded DNA molecule of around 1.1 megabases, encoding around 979 genes. This is comparable to the genome of some small bacteria. It encodes several proteins that had not been previously discovered in viruses, including aminoacyl tRNA synthetases.
APMV is as large as some small species of bacteria. When it was first discovered in 1992, it was thought to be a bacterium, and named Bradfordcoccus. APMV was not shown to be a virus until 2003, when it was the largest virus then discovered. It has since been overtaken by Megavirus chilensis, Pandoravirus and Pithovirus, all of which also infect amoebae. These and other large viruses have been called "nucleocytoplasmic large DNA viruses", an informal grouping of very large and complex DNA viruses.
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- ...that in the name of science, American nurse Clara Maass (pictured) volunteered to be bitten by yellow fever-carrying mosquitoes seven times, caught the disease twice, and ultimately died from it?
- ...that obesity, Alzheimer's disease and cancer have been associated with infectious pathogens?
- ...that the village of Cellardyke in Fife, Scotland, is the site of the first confirmed case of H5N1 avian flu in the United Kingdom?
- ...that Australian Edward Both invented the Both respirator, an iron lung made from plywood, to fight a polio epidemic in 1937?
- ...that the award-winning film Frank's Cock is split into quadrants to symbolise the "fragmentation of the body" experienced by those with AIDS?
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Thomas Flewett (29 June 1922 – 12 December 2006) was a British–Irish virologist and an authority on electron microscopy of viruses, best known for his role in the discovery of rotaviruses. After Ruth Bishop and others discovered viruses associated with diarrhoea, Flewett showed that they could be visualised by electron microscopy directly in faeces. He dubbed them "rotaviruses" for their wheel-shaped appearance. His group described the different rotavirus serotypes, and did extensive research on the rotavirus varieties infecting many animals.
Flewett established one of the first English virus laboratories in Birmingham in 1956. In addition to his rotavirus work, he discovered the cause of hand, foot and mouth disease, identified two new species of adenovirus, and co-discovered human torovirus and picobirnaviruses. His other research included influenza, coxsackie A, coxsackie B and hepatitis B viruses.
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
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Ribavirin is a nucleoside analogue, which mimics the nucleosides adenosine and guanosine. It is active against a wide range of DNA and RNA viruses, including influenza virus, herpes simplex virus, yellow fever, hepatitis C, West Nile, dengue fever and other flaviviruses, and is the only known treatment for the viruses causing viral haemorrhagic fevers. First synthesised in 1970 by Joseph T. Witkowski, ribavirin was originally developed as an anti-influenza drug, but failed to gain approval for this indication in the US. It has been used in an aerosol formulation against respiratory syncytial virus-related diseases in children. Ribavirin's main current use is against hepatitis C, in combination with pegylated interferon. Clinical use is limited by the drug building up in red blood cells to cause haemolytic anaemia. Its derivative and prodrug taribavirin, currently in clinical development, shows a similar spectrum of antiviral activity with reduced toxicity.
A selection of recent articles of interest include:
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