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Viruses are smallinfectious agents that can replicate only inside the livingcells of an organism. Viruses infect all forms of life, includinganimals,plants,fungi,bacteria andarchaea. They are found in almost everyecosystem on Earth and are the most abundant type of biological entity, with millions of different types, although only about 6,000 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 ofgenetic material, which can be eitherDNA orRNA, wrapped in aprotein coat called thecapsid; some viruses also have an outerlipidenvelope. The capsid can take simplehelical oricosahedral 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 anoptical microscope.
The origins of viruses are unclear: some may haveevolved fromplasmids, 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".
Meningitis is anacuteinflammation of themeninges, protective membranes covering thebrain andspinal cord. Symptoms in adults includeheadache,fever andneck stiffness, as well as sometimesconfusion or alteredconsciousness, vomiting, and aninability to tolerate light orloud noises. Children often show onlynonspecific symptoms, such as irritability or drowsiness.
The most common cause is infection withviruses includingenteroviruses,herpes simplex virus (mainly HSV-2),varicella zoster virus,mumps virus,HIV andlymphocytic choriomeningitis. In Western countries,viral meningitis occurs in around 11 people per 100,000 each year. Infection withbacteria,fungi,protozoa and parasites can also cause meningitis, and there are several non-infectious causes. Although some forms of meningitis can be life-threatening, viral meningitis is generally more benign than that caused by bacterial infection. It usually resolves spontaneously and is rarely fatal. HSV-2 can cause a chronic, recurrent form calledMollaret's meningitis.
Polymerase chain reaction ofcerebrospinal fluid andidentification of antibodies can be used to differentiate between viral causes. Viral meningitis typically only requires supportive therapy; meningitis caused by HSV or varicella zoster virus sometimes responds to treatment withantiviral drugs such asaciclovir. Mumps-associated meningitis can be prevented byvaccination.
Haemagglutinin, aglycoprotein trimer on theinfluenza virusenvelope, binds to thesialic acid-containingreceptor on the host cell. After the virus has been engulfed into anendosome, it changes configuration, causing the viral and endosomal membranes to fuse, releasing the viralgenome into thecytoplasm.
Credit: Jawahar Swaminathan (EBI) (16 November 2008)
26 February: In theongoing pandemic ofsevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more than 110 million confirmed cases, including 2.5 million deaths, have been documented globally since the outbreak began in December 2019.WHO
18 February: Seven asymptomatic cases ofavian influenza A subtype H5N8, the first documented H5N8 cases in humans, are reported inAstrakhan Oblast, Russia, after more than 100,0000 hens died on a poultry farm in December.WHO
14 February: Seven cases ofEbola virus disease are reported inGouécké, south-eastGuinea.WHO
7 February: A case of Ebola virus disease is detected inNorth Kivu Province of theDemocratic Republic of the Congo.WHO
4 February: An outbreak ofRift Valley fever is ongoing inKenya, with 32 human cases, including 11 deaths, since the outbreak started in November.WHO
21 November: The USFood and Drug Administration (FDA) givesemergency-use authorisation tocasirivimab/imdevimab, a combinationmonoclonal antibody (mAb) therapy for non-hospitalised people twelve years and over with mild-to-moderateCOVID-19, after granting emergency-use authorisation to the single mAbbamlanivimab earlier in the month.FDA 1,2
18 November: The outbreak ofEbola virus disease inÉquateur Province,Democratic Republic of the Congo, which started in June, has been declared over; a total of 130 cases were recorded, with 55 deaths.UN
Interferons are a group ofsignalling proteins released byhost cells in response toviruses and otherpathogens. They belong to a large class of proteins known ascytokines: molecules used for communication between cells to trigger the protective defences of theimmune system that help to eradicate pathogens. More than twenty distinct interferon genes and proteins have been identified in animals, including humans.
When a cell is infected by a virus, several virus products, includingglycoproteins and viral RNA, stimulate the cell to produce and release interferons. This causes nearby cells to heighten their defences against viral infection, and so interferes withviral replication. Some viruses, includingJapanese encephalitis virus,dengue type 2 virus,human cytomegalovirus andKaposi's sarcoma-associated herpesvirus, have evolved ways to resist interferon's antiviral activity. Interferons also have various other functions in regulating the immune system. Interferons and other cytokines are responsible for some symptoms of infection, such asfever,muscle pain and "flu-like symptoms".
The2001 foot-and-mouth outbreak included 2,000 cases ofthe disease in cattle and sheep across the UK. The source was aNorthumberland farm where pigs had been fed infected meat that had not been adequately sterilised. The initial cases were reported in February. The disease was concentrated in western and northern England, southern Scotland and Wales, withCumbria being the worst-affected area. A small outbreak occurred in the Netherlands, and there were a few cases elsewhere in Europe.
The UK outbreak was controlled by the beginning of October. Control measures included stopping livestock movement and slaughtering over 6 million cows and sheep. Public access to farmland andmoorland was also restricted(pictured), greatly reducingtourism in affected areas, particularly in theLake District. Vaccination was used in the Netherlands, but not in the UK due to concerns that vaccinated livestock could not be exported. The outbreak cost an estimated £8 billion in the UK.
| “ | 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. | ” |
Viruses & Subviral agents:bat virome •elephant endotheliotropic herpesvirus •HIV •introduction to viruses
•Playa de Oro virus •poliovirus •prion •rotavirus •virus
Diseases:colony collapse disorder •common cold •croup •dengue fever •gastroenteritis •Guillain–Barré syndrome •hepatitis B •hepatitis C •hepatitis E •herpes simplex •HIV/AIDS •influenza •meningitis •myxomatosis •polio •pneumonia •shingles •smallpox
Epidemiology & Interventions:2007 Bernard Matthews H5N1 outbreak •Coalition for Epidemic Preparedness Innovations •Disease X •2009 flu pandemic •HIV/AIDS in Malawi •polio vaccine •Spanish flu •West African Ebola virus epidemic
Virus–Host interactions:antibody •host •immune system •parasitism •RNA interference
Methodology:metagenomics
Social & Media:And the Band Played On •Contagion •"Flu Season" •Frank's Cock •Race Against Time: Searching for Hope in AIDS-Ravaged Africa •social history of viruses • "Steve Burdick" •"The Time Is Now" • "What Lies Below"
People:Brownie Mary •Macfarlane Burnet •Bobbi Campbell •Aniru Conteh •people with hepatitis C •HIV-positive people •Bette Korber •Henrietta Lacks •Linda Laubenstein •Barbara McClintock •poliomyelitis survivors •Joseph Sonnabend •Eli Todd •Ryan White
Acanthamoeba polyphaga mimivirus (APMV) is a species ofDNA virus in theMimivirusgenus of theMimiviridae family. It infects theamoeba,Acanthamoeba polyphaga. Its non-envelopedicosahedralcapsid is 400 nm in diameter, with protein filaments of 100 nm projecting from its surface. The APMVgenome is a linear, double-strandedDNA molecule of around 1.2 megabases, encoding around 979genes. This is comparable to the genome of some smallbacteria. It encodes severalproteins that had not been previously discovered in viruses, includingaminoacyl tRNA synthetases. APMV is itself parasitised by theSputnik virophage(arrowed in micrograph).
APMV is as large as some small species of bacteria, such asRickettsia conorii andTropheryma whipplei. When it was first discovered in 1992, it was thought to be a bacterium, and namedBradfordcoccus. APMV was not shown to be a virus until 2003, when it was the largest virus then discovered. It has since been overtaken byMegavirus chilensis,Pandoravirus andPithovirus, all of which also infect amoebae. These and other large and complex DNA viruses are now grouped inNucleocytoviricota, also termed nucleocytoplasmic large DNA viruses.
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Edward Jenner (1749–1823) was an English physician and scientist who pioneered thesmallpox vaccine, the world's firstvaccine. Noting the common observation that milkmaids were generally immune tosmallpox, Jenner postulated that thepus in the blisters that milkmaids received fromcowpox (a similar but much less virulent disease) protected them from smallpox. In 1796, Jenner tested his hypothesis by inoculating an eight-year-old boy with pus from an infected milkmaid. He subsequently repeatedly challenged the boy withvariolous material, then the standard method of immunisation, without inducing disease. He published a paper including 23 cases in 1798. Although several others had previously inoculated subjects with cowpox, Jenner was the first to show that the procedure inducedimmunity to smallpox. He later successfully popularised cowpox vaccination.
Jenner is often called "the father of immunology", and his work is said to have saved more lives than that of any other individual.
7 November 1991:Magic Johnson announced his retirement from basketball because of his infection withHIV
14 November 1957:Kuru, the first humanprion disease, described byDaniel Gajdusek and Vincent Zigas
16 November 2002: Thefirst case ofsevere acute respiratory syndrome(virus pictured) recorded inGuangdong, China
17 November 1995:Lamivudine approved for treatment of HIV
22 November 2013:Simeprevir approved for treatment of chronichepatitis C virus infection
23 November 1978: Structure oftomato bushy stunt virus solved by Stephen Harrison and colleagues, the first atomic-level structure of a virus
24 November 2007: Outbreak of new Ebola species,Bundibugyo virus
26 November 1898:Martinus Beijerinck coined the termcontagium vivum fluidum to describe the agent causingtobacco mosaic disease
Severalhuman papillomavirus (HPV) vaccines, includingCervarix andGardasil, have been approved to protect against infections with particular types ofHPV, associated withcervical and other cancers. All vaccines protect against the high-risk HPV types 16 and 18. Gardasil is a quadrivalent vaccine that additionally protects against low-risk HPV-6 and -11, which are associated with most cases ofgenital warts. A second-generation nine-valent Gardasil vaccine protects against five additional high-risk HPV types. It is estimated that the vaccines may prevent 70% of cervical cancer, 80% ofanal cancer, 60% ofvaginal cancer, 40% ofvulvar cancer and possibly someoropharyngeal cancers. Protection lasts for at least 8–9 years. Some advocate giving Gardasil to men and boys with the primary aim of protecting their female sexual partners; others consider vaccinating only women and girls to be more cost effective. The licensed vaccines aresubunit vaccines, containing only the L1capsid protein of the virus, which self-assembles intovirus-like particles. They are not effective in people already infected with HPV. Research is ongoing into therapeutic HPV vaccines including the viraloncoproteins, E6 and E7, but none has yet been licensed.
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WikiProject VirusesRelated WikiProjectsMedicine •Microbiology •Molecular & Cellular Biology •Veterinary Medicine
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