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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.
Influenza, or flu, is aninfectious disease caused by someorthomyxoviruses, that affectsbirds and somemammals including humans, horses and pigs. Influenza is predominantlytransmitted through the air by coughs or sneezes, creatingaerosols containing the virus. It can also be transmitted by contact with bird droppings ornasal secretions, or by touching contaminated surfaces. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection. Around a third of cases show no symptoms. The most common symptoms includefever,runny nose,sore throat,muscle pains,headache,cough andfatigue. Influenza is occasionally associated withnausea andvomiting, particularly in children.Pneumonia is a rare complication which can be life-threatening.
Influenza spreads around the world inseasonal epidemics, resulting in about 3–5 million cases of severe illness annually, and about 250,000–500,000 deaths, mainly in the young, the old and those with other health problems. Annualinfluenza vaccinations are recommended for those at high risk. Sporadicinfluenza pandemics have been recorded since at least the 16th century. TheSpanish flu pandemic of 1918–20 is estimated to have killed 50–100 million people.
False-coloured transmission electron micrograph ofsevere acute respiratory syndrome coronavirus 2, a novelcoronavirus, showing the spikes (blue) forming a crown that give this group of RNA viruses their name. The spike protein interacts with the cellular receptor for the virus,angiotensin-converting enzyme 2.
Credit:National Institute of Allergy and Infectious Diseases (13 February 2020)
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
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Bats host a diverse array of viruses, including all seven types described by theBaltimore classification system. The most common viruses known to infectbats arecoronaviruses. Bats harbour many viruses that arezoonotic, or capable of infecting humans, includingrabies virus,SARS-CoV,SARS-CoV-2,MERS-CoV,Nipah virus,Hendra virus andMarburg virus (hosted by theEgyptian fruit bat;pictured), and some bat-borne viruses are considered importantemerging viruses. Bats may also play a role in theecology of theEbola virus. Most zoonotic bat viruses are transmitted by direct contact with infected bat fluids such as urine,guano and saliva, or through contact with an infectedintermediate host; transmission of rabies from bats to humans usually occurs via biting. Butchering or consumingbat meat could potentially lead to viral transmission.
Bats rarely become ill from viral infections, andrabies is the only viral disease known to kill them. They might be more tolerant of infection than other mammals. Theirimmune systems differ from those of other mammals in their lack of severalinflammasomes, which activate the body's inflammatory response, as well as a dampenedstimulator of interferon genes response, which helps to control the host response to pathogens.
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In thesevere acute respiratory syndrome (SARS) outbreak, the first cases of the newly emergedSARS coronavirus were reported in November 2002 from the ChineseGuangdong province. The virus soon spread across Asia, with China, Hong Kong, Taiwan and Singapore being the worst affected countries; a secondary outbreak occurred in Canada. The rapid initial spread of the outbreak has been in part attributed to China's slow response to the early cases. Over 8,000 people were infected, with acase fatality rate of 11%. Those over 65 years had a much higher mortality rate, greater than 55%. The outbreak was contained by July 2003, and no cases have been reported since 2004.
At the time of the outbreak, the immediate source of SARS coronavirus was thought to have been themasked palm civet (Paguma larvata;pictured), which was sold as food in Guangdong markets. The virus was also found inraccoon dogs,ferret badgers and domestic cats. More recent research has suggested that the natural reservoir could behorseshoe bats.
| “ | Some scientists visualize the virus as an ill-defined shape emerging bashfully out of a dense and golden cloud. This is a beautiful and romantic vision. Virology should, however, not be too Turnerian. Nor should it be an abstract art. The portrait of a virus should not produce an aesthetic emotion by means of an organic disturbance. | ” |
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
Cauliflower mosaic virus (CaMV) is a plantpararetrovirus in theCaulimoviridae family, which has similarities withhepadnaviruses such ashepatitis B virus. It predominantly infects members of theBrassicaceae (cabbage) family, includingcauliflower andturnip; some strains can also infectDatura andNicotiana species of theSolanaceae family. It is transmitted byaphidvectors, such asMyzus persicae. Symptoms include a mottled leaf pattern called "mosaic",necrotic lesions on the surface of infected leaves, stunted growth and deformation of the overall plant structure.
Although the viralgenome is double-stranded DNA, the virus replicates viareverse transcription like aretrovirus. Theicosahedral virion is 52 nm in diameter, and is built from 420capsid protein subunits. The circular 8 kb genome encodes seven proteins, including amovement protein, which facilitates viral movement to neighbouring cells, and an insect transmission factor, which recognises a protein receptor at the tip of the aphid mouthparts(pictured). CaMV has several ways of evading the host defensive responses, which include interruptingsalicylic acid-dependent signalling and decoying host silencing machinery. The virus has a strong constitutive (always on)promoter, CaMV 35S, which is widely used in plantgenetic engineering.
Françoise Barré-Sinoussi (born 30 July 1947) is a Frenchvirologist, known for being one of the researchers who discoveredHIV.
Barré-Sinoussi researchedretroviruses inLuc Montagnier's group at theInstitut 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 inlymph node tissue, which they called "lymphadenopathy-associated virus". Their results were published simultaneously with those ofRobert 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 causeAIDS. Barré-Sinoussi continued to research HIV until her retirement in 2015, studying how the virus istransmitted from mother to child, theimmune response to HIV, and how a small proportion of infected individuals, termed "long-term nonprogressors", can limit HIV replication withouttreatment. In 2008, she was awarded theNobel Prize, with Montagnier, for the discovery of HIV.
February 1939: First virology journal,Archiv für die gesamte Virusforschung, appeared
8 February 1951: Establishment of theHeLa cell line from acervical carcinoma biopsy, the first immortal human cell line
12 February 1892:Dmitri Ivanovsky(pictured) demonstrated transmission oftobacco mosaic disease by extracts filtered throughChamberland filters; sometimes considered the beginning of virology
19 February 1966:Prion diseasekuru shown to be transmissible
23 February 2018:Baloxavir marboxil, the first anti-influenza agent to target the cap-dependentendonuclease activity of the viral polymerase, approved in Japan
27 February 2005:H1N1 influenza strain resistant tooseltamivir reported in a human patient
24 February 1977:Phi X 174 sequenced byFred Sanger and coworkers, the first virus and the first DNA genome to be sequenced
28 February 1998: Publication ofAndrew Wakefield'sLancet paper, subsequently discredited, linking theMMR vaccine with autism, which started theMMR vaccine controversy
Zidovudine (ZDV) (also known asAZT and sold asRetrovir) is anantiretroviral drug used in the prevention and treatment ofHIV/AIDS. Classed as anucleoside analogue reverse-transcriptase inhibitor, it inhibits HIV'sreverse transcriptaseenzyme, which copies the viral RNA into DNA and is essential for itsreplication. The first breakthrough in AIDS therapy, ZDV was licensed in 1987. While it significantly reduces HIV replication, leading to some clinical and immunological benefits, when used alone ZDV does not completely stop replication, allowing the virus to become resistant to it. The drug is therefore used together with other anti-HIV drugs in combination therapy calledhighly active antiretroviral therapy. To simplify its administration, ZDV is included in combination pills withlamivudine (Combivir) and lamivudine plusabacavir (Trizivir). ZDV continues to be used to prevent HIV transmission frommother to child during childbirth; it was previously part of the standardpost-exposure prophylaxis afterneedlestick injury.
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