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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Rabies is a disease of humans and other mammals, caused by the rabies virus, an RNA virus in the Rhabdoviridae family. Dogs and bats are the most important source of human infections; other natural hosts include monkeys, raccoons, foxes, skunks, cattle, wolves, coyotes, cats, mongooses, bears, groundhogs, weasels and other carnivores. Transmission is commonly via saliva, usually from bites, but can also occur via aerosols contacting mucous membranes. The typical human incubation period is 2–12 weeks. The neurotropic virus travels along neural pathways into the CNS and brain, where it causes encephalitis. Flu-like symptoms are followed by neurological symptoms, including partial paralysis, hydrophobia, confusion, agitation, paranoia and hallucinations, which progress to delirium and death. An estimated 26,000 people died from rabies in 2010, mainly in Asia and Africa.
Rabies is mentioned in the Codex of Eshnunna of around 1930 BC. The first vaccine was developed in 1885 by Louis Pasteur and Émile Roux. Prophylactic vaccination is used in people at high risk, pets and wild animals. Post-exposure prophylaxis, including vaccine and immunoglobulin, is completely effective if begun immediately after exposure, but survival is rare once symptoms have begun. Five of 36 people lived after receiving the experimental Milwaukee protocol.
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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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| “ | ...in a flash I had understood: what caused my clear spots was, in fact, an invisible microbe, a filterable virus, but a virus parasitic on bacteria. | ” |
—Félix d'Herelle on the discovery of bacteriophages
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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Papillomaviruses are small non-enveloped DNA viruses that make up the Papillomaviridae family. Their circular double-stranded genome is around 8 kb. The icosahedral capsid is 55–60 nm in diameter. They infect humans, other mammals and some other vertebrates including birds, snakes and turtles. More than a hundred species are known, classified into 30 genera. All papillomaviruses replicate exclusively in epithelial cells of stratified squamous epithelium, which forms the skin and some mucosal surfaces, including the lining of the mouth, airways, genitals and anus.
Infection by most papillomaviruses is either asymptomatic or causes small benign tumours known as warts or papillomas. Francis Peyton Rous showed in 1935 that the cottontail rabbit papilloma virus could cause skin cancer in rabbits – the first time that a virus was shown to cause cancer in mammals – and papillomas caused by some virus types, including human papillomavirus 16 and 18, carry a risk of becoming cancerous if the infection persists. Papillomaviruses are associated with cancers of the cervix, vulva, vagina, penis, oropharynx and anus in humans.
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- ...that flow cytometry bioinformaticians use methods from computational statistics and machine learning to analyse single cell data gathered by flow cytometry for cancer and HIV/AIDS research (output pictured)?
- ...that Sierra Leonean physician Aniru Conteh saved thousands of lives from Lassa fever before dying from the disease himself?
- ...that early in the history of veterinary medicine in the Philippines, a cattle plague killed 600,000 animals from 1901 to 1902 alone?
- ...that the isolation of antibodies and flu viruses from birds on Tryon Island, a coral cay off the coast of Queensland, Australia, led to the development of antiviral drugs, such as oseltamivir?
- ...that the Plague of Athens devastated ancient Athens in 430 BC, perhaps leading ultimately to the city's defeat in the Peloponnesian War?
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Walter Reed (13 September 1851 – 22 November 1902) was an American physician in the U.S. Army medical corps who is known for his research on the epidemiology of yellow fever, at a time when viruses had only just been discovered.
Reed started to study yellow fever in the USA in the 1890s, showing that walking through swampy woods at night was associated with the disease, while drinking water from the Potomac River was not. In 1900, he led an army commission under the direction of George Miller Sternberg to investigate yellow fever in Cuba, where the disease was endemic. Building on Carlos Finlay's work suggesting that yellow fever was transmitted by a particular species of mosquito acting as a vector, Reed and co-workers confirmed Finlay's results, and also disproved the popular idea that the disease was transmitted by contaminated objects, such as clothing or bedding. The experiments involved the deliberate infection of human volunteers, several of whom died of yellow fever, and Reed pioneered the concept of medical consent.
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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Nevirapine (also Viramune) is an antiretroviral drug used in the treatment of HIV/AIDS. It was the first non-nucleoside reverse transcriptase inhibitor to be licensed, which occurred in 1996. Like nucleoside inhibitors, nevirapine inhibits HIV's reverse transcriptase enzyme, which copies the viral RNA into DNA and is essential for its replication. However, unlike nucleoside inhibitors, it binds not in the enzyme's active site but in a nearby hydrophobic pocket, causing a conformational change in the enzyme that prevents it from functioning. Mutations in this pocket generate resistance to nevirapine, which develops rapidly unless viral replication is completely suppressed. The drug is therefore used together with other anti-HIV drugs in combination therapy called highly active antiretroviral therapy (HAART). A single dose of nevirapine is a cost-effective way to reduce mother-to-child transmission of HIV, and has been recommended by the World Health Organization for use in resource-poor settings. Rash is the most common adverse event associated with the drug.
A selection of recent articles of interest include:
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