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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Hepatitis C is an infectious disease affecting primarily the liver, caused by hepatitis C virus (HCV), an RNA virus of the Flaviviridae family which infects humans and chimpanzees. A "non-A non-B hepatitis" was postulated in the 1970s, and HCV was demonstrated in 1989. HCV is spread primarily by blood-to-blood contact associated with intravenous drug use in the developed world, and with poorly sterilised medical equipment and transfusions in the developing world. In about 80% of those infected, the virus persists in the liver, and around 10–30% of those infected will develop cirrhosis over 30 years. Some people with cirrhosis go on to develop liver failure, liver cancer or other complications.
An estimated 150–200 million people worldwide are infected with HCV. Hepatitis C causes 27% of cirrhosis cases and 25% of hepatocellular carcinoma (a form of liver cancer) worldwide, and is the leading reason for liver transplantation. The standard therapy for persistent infection is a combination of the antiviral drug ribavirin with pegylated interferon, sometimes plus one of the protease inhibitors, boceprevir or telaprevir. Overall, 50–80% of people treated are cured. No vaccine against hepatitis C 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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| “ | A virus is a piece of bad news wrapped in protein. | ” |
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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Adeno-associated viruses (AAVs) are small DNA viruses in the Parvoviridae family. They cannot complete their replication cycle without a helper virus, either an adenovirus or herpesvirus. In the absence of the helper, AAV integrates into the host genome at a specific site on human chromosome 19. The 20 nm icosahedral capsid lacks an envelope, and contains a single-stranded DNA genome of around 4.7 kb. AAV infects humans and some other primates without causing disease. It generates only a mild immune response, which consists mainly of neutralising antibodies. The best-studied serotype, AAV-2, infects nerve cells, liver cells, skeletal muscle and the smooth muscle of blood vessels, using heparan sulphate proteoglycan as its receptor.
Its low pathogenicity makes AAV an attactive basis for viral vectors for gene therapy. Alipogene tiparvovec to treat lipoprotein lipase deficiency was the first gene therapy to be licensed. Promising results have also been obtained in clinical trials with AAV-based gene therapy in haemophilia, congestive heart disease, Parkinson's disease and the rare eye disease Leber's congenital amaurosis.
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- ...that murine polyomavirus (pictured) is an oncovirus that causes tumours in newborn mice?
- ...that Pat Nuttall showed that systemic infection of the host is not required for pathogens such as tick-borne encephalitis virus to be transmitted between vectors?
- ...that the first person to die in Australia from the 2009 flu was a Pintupi man whose people gave up hunting to settle the remote community of Kiwirrkura at the time of his birth?
- ...that the 2011 film Asmaa is the first feature-length Egyptian drama film to present AIDS patients sympathetically?
- ...that the anti-vaccine book Melanie's Marvelous Measles has received over 1,000 one-star reviews on Amazon.com?
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Françoise Barré-Sinoussi (born 30 July 1947) is a French virologist, known for being one of the researchers who discovered HIV.
Barré-Sinoussi researched retroviruses in Luc Montagnier's group at the Institut Pasteur in Paris. In 1982, she and her co-workers started to analyse samples from people with a new disease, then referred to as "gay-related immune deficiency". They found a novel retrovirus in lymph node tissue, which they called "lymphadenopathy-associated virus". Their results were published simultaneously with those of Robert Gallo's group in the USA, who had independently discovered the virus under the name "human T-lymphotropic virus type III". The virus, renamed "human immunodeficiency virus", was later shown to cause AIDS. Barré-Sinoussi has continued to research HIV, studying how the virus is transmitted from mother to child, the immune response to HIV, and how a small proportion of infected individuals, termed "long-term nonprogressors", can limit HIV replication without treatment. In 2008, she was awarded the Nobel Prize, with Montagnier, for the discovery of HIV.
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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Oseltamivir (also Tamiflu) is an oral antiviral drug against influenza (flu). It was the second inhibitor of the viral neuraminidase to be developed, after zanamivir, and the first to be taken as an oral tablet. It was originally synthesised from shikimic acid extracted from the star anise plant. Oseltamivir is a prodrug that requires metabolism in the liver to the active form, oseltamivir carboxylate. This binds at the active site of the neuraminidase enzyme, preventing it from cleaving sialic acid to release the virus particle from the host cell. If taken within 48 hours of infection, oseltamivir reduces the duration of influenza symptoms by about a day. Debate is ongoing about whether it also reduces the risk of complications, such as pneumonia. Nausea and vomiting are the main adverse events. Resistance to oseltamivir has been observed in some strains of influenza virus, especially H1N1 strains, but cross-resistance to zanamivir is rare.
A selection of recent articles of interest include:
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