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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Chickenpox is an infectious disease caused by primary infection with varicella zoster virus, a DNA virus of the Alphaherpesvirinae subfamily. The virus infects humans and some other primates and is transmitted by the respiratory route. Symptoms appear 10–21 days after exposure: an itchy vesicular skin rash mainly concentrated on the torso and head, and small ulcers in the oral cavity and tonsil areas. After the rash resolves, the virus remains latent in nerve cell bodies, and can emerge years or decades later to cause shingles.
A classic disease of childhood, the highest prevalence occurs at 4–10 years. Chickenpox is rarely fatal in people with a normal immune system, with around 6,800 deaths worldwide in 2010. Adults tend to experience more severe symptoms than children, and are at higher risk of complications such as pneumonia, hepatitis and encephalitis. Pregnant women and people with a suppressed immune system have the highest risk of serious complications. Chickenpox during the first 28 weeks of gestation can lead to foetal malformations. Infection in adults is usually treated with antiviral drugs, such as aciclovir or valaciclovir, which reduces both symptom severity and the risk of complications. A vaccine is available.
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Rinderpest was a Morbillivirus that caused catastrophic cattle plagues for centuries. It was declared the second virus to have been eradicated globally in 2011.
Credit: Jacobus Eussen (1745)
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Vaccination or immunisation is the administration of antigenic material (a vaccine) to stimulate an individual's immune system to develop adaptive immunity to a virus or other pathogen. The active agent of a vaccine may be intact but inactivated (non-infective) or attenuated (with reduced infectivity) forms of the pathogen, or purified components that have been found to be highly immunogenic, 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. Widespread immunity due to mass vaccination campaigns is largely responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio and measles from much of the world. Vaccination efforts have been met with some controversy since their inception, on scientific, ethical, political, medical safety, and religious grounds.
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 1918 flu pandemic was an unusually deadly influenza pandemic, the first of the two involving H1N1 influenza virus. The pandemic's geographic origin is unknown. Lasting from January 1918 until December 1920, it infected 500 million people across the entire globe, with a death toll of 50–100 million (3–5% of the world's population), making it one of the deadliest natural disasters of human history. It was also implicated in the outbreak of encephalitis lethargica in the 1920s.
Most influenza outbreaks disproportionately kill young, elderly or already weakened patients; in contrast the 1918 pandemic predominantly killed healthy young adults. Modern research suggests that the virus kills through a cytokine storm, an overreaction of the body's immune system. The strong immune reactions of young adults resulted in a more severe disease with a higher mortality rate, whereas the weaker immune systems of children and older adults resulted in fewer deaths.
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| “ | An inefficient virus kills its host. A clever virus stays with it. | ” |
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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Noroviruses are a genus of non-enveloped, single-stranded RNA viruses in the Caliciviridae family. The positive-sense RNA genome is approximately 7.5 kbp. Known noroviruses fall into five different genogroups (GI–GV); three groups infect humans, the other two mice, cattle and other bovines. All are considered strains of a single species, Norwalk virus.
Noroviruses are extremely contagious, with fewer than 20 virus particles being infectious. They are transmitted directly from person to person and indirectly via contaminated water and food. After infection, the virus replicates in the small intestine, causing acute gastroenteritis, which develops 24–48 hours after exposure and lasts for 24–60 hours. The characteristic symptoms include nausea, forceful vomiting, watery diarrhoea and abdominal pain. Infection is usually self-limiting and rarely severe. Noroviruses are the most common cause of viral gastroenteritis in humans, affecting around 267 million people a year and causing over 200,000 deaths, mainly in less-developed countries and in very young, elderly or immunosuppressed people. Hand washing with soap and water is effective in reducing transmission.
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- ...that in 1974, Rudolf Jaenisch and Beatrice Mintz created the first transgenic mouse (example pictured) by injecting DNA from simian virus 40?
- ...that double-stranded RNA viruses cause everything from gastroenteritis in young children to bluetongue disease in livestock?
- ...that Inventing the AIDS Virus, written by molecular biologist Peter Duesberg, argues that AIDS is not infectious and that HIV is an unrelated passenger virus?
- ..that during the 1967 outbreak of foot and mouth disease in the United Kingdom, around 430,000 animals were slaughtered?
- ...that proteins from pokeweed have shown antiviral properties?
Lua error in package.lua at line 80: module 'Module:Box-header/colours' not found. Rosalind Elsie Franklin (25 July 1920 – 16 April 1958) was a British biophysicist and X-ray crystallographer who made critical contributions to the understanding of the fine molecular structures of DNA, RNA and viruses.
Franklin led pioneering research on the structure of tobacco mosaic virus (TMV), a rod-like RNA virus, using X-ray crystallography. She first showed that, contrary to contemporary opinion, TMV virus particles were all of the same length. With Kenneth Holmes, she showed the virus's coat is composed of protein molecules arranged in helices. She designed and built a model of the virus to be exhibited at the 1958 World's Fair. She speculated that the virus is hollow, and correctly hypothesized that the RNA of TMV is single-stranded. Her work, together with that of Donald Caspar, revealed that the viral RNA is wound along the inner surface of the hollow virus. Her laboratory, which also included Aaron Klug, studied other plant viruses, including turnip yellow mosaic virus and viruses infecting potato, tomato and pea. Franklin also worked on icosahedral animal viruses, including poliovirus.
Franklin is commemorated in the Rosalind Franklin University of Medicine and Science.
1 April 1911: Peyton Rous showed that a cell-free isolate could transmit sarcoma in chickens, an early demonstration of cancer caused by a virus
7 April 1931: First electron micrograph taken by Ernst Ruska and Max Knoll
8 April 1976: Bacteriophage MS2 (pictured) sequenced by Walter Fiers and coworkers, first viral genome to be completely sequenced
8 April 1990: Death from AIDS of Ryan White, haemophiliac teenager for whom the Ryan White Care Act is named
8 April 1992: Tennis player Arthur Ashe announced that he had been infected with HIV from blood transfusions
9 April 1982: Stanley Prusiner proposed proteinaceous prions as the cause of scrapie
12 April 1955: Success of trial of Jonas Salk's polio vaccine announced
12 April 2013: New order of double-stranded DNA bacteriophages, Ligamenvirales, announced
15 April 1957: André Lwoff proposes a concise definition of a virus
21 April 1989: Discovery of hepatitis C virus by Qui-Lim Choo and colleagues
28 April 1932: First yellow fever vaccine announced at an American Societies for Experimental Biology meeting by Wilbur Sawyer
29 April 2015: PAHO and WHO declared the Americas region free from rubella transmission
30 April 1937: Discovery of Theiler's murine encephalomyelitis virus, later a model for multiple sclerosis research
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Two polio vaccines are used against the paralytic disease polio. Each vaccine has benefits and disadvantages. The first, developed by Jonas Salk, consists of inactivated poliovirus. Based on three wild virulent strains, inactivated using formalin, it is administered by injection. 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, consists of three live virus strains, attenuated by growth in cell culture. They contain multiple mutations, stopping them from replicating in the nervous system. The Sabin vaccine provides longer-lasting immunity than the Salk vaccine, and can be administered orally, making it more suitable for mass vaccination campaigns. In around 1 in 750,000 people, the live vaccine reverts to a virulent form and causes paralysis. Vaccination has reduced the number of polio cases from around 350,000 in 1988 to just 223 in 2012, and eradicated the disease from most countries.
A selection of recent articles of interest include:
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