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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Yellow fever is an acute haemorrhagic fever caused by the yellow fever virus, an RNA virus in the Flaviviridae family. It infects humans, other primates, and Aedes aegypti and other mosquito species, which act as the vector. After transmission by the bite of a female mosquito, the virus replicates in lymph nodes, infecting dendritic cells, and can then spread to liver hepatocytes. Symptoms generally last 3–4 days, and include fever, nausea and muscle pain. In around 15% of people, a toxic phase follows with recurring fever, liver damage, jaundice and bleeding; death occurs in around a fifth of these cases. Infection otherwise leads to lifelong immunity.
The first recorded outbreak of yellow fever was in Barbados in 1647, and major epidemics have occurred in the Americas, Africa and Europe since that date. Yellow fever is endemic in tropical and subtropical areas of South America and Africa; its incidence has been increasing since the 1980s. An estimated 200,000 cases and 30,000 deaths occur each year, with almost 90% of cases being in Africa. Antiviral therapy is not effective. A vaccine is available, and vaccination, mosquito control and bite prevention are the main preventive measures.
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The first immortal human cell line, HeLa cells were derived from a cervical cancer biopsy and carry human papillomavirus 18 DNA. The cells have been growing since 1951.
Credit: Gerry Shaw (8 March 2012)
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Bacteriophages (or phages) are a large and diverse group of viruses that infect bacteria and archaea. Their genome, which they inject into the host's cytoplasm, can be DNA or RNA, single or double stranded, linear or circular, and contains between four and several hundred genes. Their capsid can be relatively simple or elaborate in structure, and in a few groups is surrounded by an envelope. Caudovirales, double-stranded DNA phages with tails, is the best-studied group, and includes T4 (pictured) and λ phage.
Among the most common entities in the biosphere, bacteriophages are widely distributed in locations populated by bacteria, such as soil and animal intestines. One of the densest natural sources is sea water, where up to 900 million virions/mL have been found in microbial mats at the surface, and up to 70% of marine bacteria can be infected.
Used as an alternative to antibiotics for over 90 years, phages might offer a potential therapy against multi-drug-resistant bacteria.
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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| “ | A virus is not an individual organism in the ordinary sense of the term, but something which could almost be called a stream of biological patterns. | ” |
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 extracts of pringamoza (pictured) have shown antiviral activity against herpes simplex?
- ...that the vaccine MVA-B has been found to create a resistance to HIV in 90% of the Phase I testers?
- ...that the Kunjin virus, which can be transmitted by mosquitoes and may cause encephalitis in humans, is named for an Indigenous Australian clan living near where the virus was first isolated?
- ...that the Gaussian network model has a wide range of applications from enzymes composed of a single domain, to large macromolecular assemblies, such as ribosomes and viral capsids?
- ...that Trinidadian virologist Joseph Lennox Pawan was the first person to show that rabies could be spread by vampire bats to other animals and humans?
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Many well-known people have survived the paralytic disease poliomyelitis. The earliest identified case might be Siptah (pictured), Egyptian pharaoh 1197–1191 BC, whose mummified remains have a deformed leg possibly from polio. Claudius, Roman emperor 41–54 AD, walked with a limp after a childhood disease that historians have hypothesised might have been polio. Novelist Sir Walter Scott suffered paralysis in one leg after a teething fever in 1773, which left him lame; his detailed account of his disease has allowed a retrospective diagnosis of polio to be made with confidence.
For many of those who survived it, paralytic polio was a life-changing experience. The disease can lead to permanent physical disability; Itzhak Perlman, for example, plays the violin seated. Others recover completely, with some going on to excel in sports; Ray Ewry became world's foremost standing jumper after childhood polio. Some survivors, including singer Ian Dury and actress Mia Farrow, have campaigned for polio eradication or for disability rights.
1 December 1988: First World AIDS Day
4 December 1915: Frederick Twort discovered bacteriophages
4 December 2009: New order of single-stranded RNA viruses, Tymovirales, announced
6 December 1995: Saquinavir approved by FDA; the first HIV protease inhibitor
6 December 2013: Sofosbuvir approved for treatment of chronic hepatitis C virus (HCV), the first HCV nucleotide analogue and the first drug approved for interferon-free treatment
9 December 1979: Global Commission for Certification of Smallpox Eradication signed document formally certifying smallpox eradication
15 December 1955: Crystallisation of poliovirus by Fred Schaffer and Carlton Schwerdt, the first animal virus to be crystallised
15 December 1967: Infectious phi X 174 synthesised by Arthur Kornberg and coworkers, the first synthetic virus
18 December 1908: Poliovirus discovered by Karl Landsteiner and Erwin Popper
25 December 1982: Lambda phage (plaques pictured) sequenced by Fred Sanger and coworkers
28 December 1936: Scrapie shown to be transmissible, the first demonstration for a prion disease
29 December 1926: Thomas Milton Rivers proposed that viruses are obligate parasites
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| “ | the most damaging medical hoax of the last 100 years —Dennis Flaherty, 2011 |
” |
The MMR vaccine controversy centered around the – now discredited – notion that the combined vaccine for measles, mumps and rubella (MMR) might be associated with colitis and autism spectrum disorders. The idea was based on a research paper by Andrew Wakefield and co-authors, published in the prestigious medical journal The Lancet in 1998, and subsequently shown to be fraudulent. Sunday Times journalist Brian Deer's investigations revealed that Wakefield had manipulated evidence and had multiple undeclared conflicts of interest. The Lancet paper was retracted in 2010; 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 significantly increased incidence of measles and mumps followed, leading to deaths and severe injuries. Multiple large epidemiological studies have found no link between the vaccine and autism.
A selection of recent articles of interest include:
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