Introduction to viruses: Difference between revisions - Wikipedia

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In 1884, French [[microbiologist]] [[Charles Chamberland]] invented the [[Chamberland filter]] (or Chamberland–Pasteur filter), that contains pores smaller than [[bacteria]]. He could then pass a solution containing bacteria through the filter, and completely remove them. In the early 1890s, Russian [[biologist]] [[Dmitri Ivanovsky]] used this method to study what became known as the [[tobacco mosaic virus]]. His experiments showed that extracts from the crushed leaves of infected tobacco plants remain infectious after filtration.<ref>{{harvnb|Shors|2017|p=6}}</ref>

At the same time, several other scientists showed that, although these agents (later called viruses) were different from bacteria and about one hundred times smaller, they could still cause disease. In 1899, Dutch microbiologist [[Martinus Beijerinck]] observed that the agent only multiplied when in [[cell division|dividing cells]]. He called it a "contagious living fluid" ({{lang-la|text= [[contagium vivum fluidum]]}})—or a "soluble living germ" because he could not find any germ-like particles.<ref>{{harvnb|Collier|Balows|Sussman|1998|p=3}}</ref> In the early 20th century, English [[bacteriologist]] [[Frederick Twort]] discovered viruses that infect bacteria,<ref>{{harvnb|Shors|2017|p=827}}</ref> and French-Canadian microbiologist [[Félix d'Herelle]] described viruses that, when added to bacteria growing on [[agar]], would lead to the formation of whole areas of dead bacteria. Counting these dead areas allowed him to calculate the number of viruses in the suspension.<ref>{{cite journal | vauthors = D'Herelle F | title = On an invisible microbe antagonistic toward dysenteric bacilli: brief note by Mr. F. D'Herelle, presented by Mr. Roux. 1917 | journal = Research in Microbiology | volume = 158 | issue = 7 | pages = 553–554 | year = 2007 | pmid = 17855060 | doi = 10.1016/j.resmic.2007.07.005 | doi-access = free }}</ref>

The invention of the [[electron microscope]] in 1931 brought the first images of viruses.<ref>From ''Nobel Lectures, Physics 1981–1990'', (1993) Editor-in-Charge Tore Frängsmyr, Editor Gösta Ekspång, World Scientific Publishing Co., Singapore</ref> In 1935, American [[biochemist]] and [[virologist]] [[Wendell Meredith Stanley]] examined the tobacco mosaic virus (TMV) and found it to be mainly made from [[protein]].<ref>{{cite journal | vauthors = Stanley WM, Loring HS | year = 1936 | title = The isolation of crystalline tobacco mosaic virus protein from diseased tomato plants | journal = Science | volume = 83 | issue = 2143| page = 85 | pmid = 17756690 | doi = 10.1126/science.83.2143.85 |bibcode = 1936Sci....83...85S }}</ref> A short time later, this virus was shown to be made from protein and [[RNA]].<ref>{{cite journal | doi = 10.1126/science.89.2311.345 | vauthors = Stanley WM, Lauffer MA | year = 1939 | title = Disintegration of tobacco mosaic virus in urea solutions |journal = Science | volume = 89 | issue = 2311| pages = 345–347 | pmid = 17788438 |bibcode = 1939Sci....89..345S }}</ref> [[Rosalind Franklin]] developed [[X-ray crystallography|X-ray crystallographic pictures]] and determined the full structure of TMV in 1955.<ref name="pmid18702397">{{cite journal | vauthors = Creager AN, Morgan GJ | title = After the double helix: Rosalind Franklin's research on Tobacco mosaic virus | journal = Isis; an International Review Devoted to the History of Science and Its Cultural Influences | volume = 99 | issue = 2 | pages = 239–272 | date = June 2008 | pmid = 18702397 | doi = 10.1086/588626 | s2cid = 25741967 }}</ref> Franklin confirmed that viral proteins formed a spiral hollow tube, wrapped by RNA, and also showed that viral RNA was a single strand, not a double helix like DNA.<ref name="Johnson">{{cite journal |last1=Johnson |first1=Ben |title=Rosalind Franklin's contributions to virology |journal=Nature Portfolio Microbiology Community |date=25 July 2017 |url=https://microbiologycommunity.nature.com/posts/18900-rosalind-franklin-s-contributions-to-virology |access-date=7 January 2022 |language=en}}</ref>

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== Origins ==

Viruses co-exist with life wherever it occurs. They have probably existed since living cells first evolved. Their origin remains unclear because they do not [[fossil]]ize, so [[Molecular biology|molecular techniques]] have been the best way to [[hypothesis]]e about how they arose. These techniques rely on the availability of ancient viral DNA or RNA, but most viruses that have been preserved and stored in laboratories are less than 90 years old.<ref>{{harvnb|Shors|2017|p=16}}</ref><ref>{{harvnb|Collier|Balows|Sussman|1998|pp=18–19}}</ref> Molecular methods have only been successful in tracing the ancestry of viruses that evolved in the 20th century.<ref name="pmid15476878">{{cite journal | vauthors = Liu Y, Nickle DC, Shriner D, Jensen MA, Learn GH, Mittler JE, Mullins JI | title = Molecular clock-like evolution of human immunodeficiency virus type 1 | journal = Virology | volume = 329 | issue = 1 | pages = 101–108 | date = November 2004 | pmid = 15476878 | doi = 10.1016/j.virol.2004.08.014| doi-access = free }}</ref> New groups of viruses might have repeatedly emerged at all stages of the evolution of life.<ref name=NRM_Krupovic2019>{{cite journal |vauthors= Krupovic M, Dooja W, Koonin EV |s2cid=169035711 |title=Origin of viruses: primordial replicators recruiting capsids from hosts. |journal=Nature Reviews Microbiology |volume=17 |issue=7 |pages=449–458 |date=2019 |doi=10.1038/s41579-019-0205-6 |pmid=31142823|url=https://hal-pasteur.archives-ouvertes.fr/pasteur-02557191/file/Krupovic_NRMICRO-19-022_MS_v3_clean.pdf }}</ref> There are three major [[Scientific theory|theories]] about the origins of viruses:<ref name=NRM_Krupovic2019 /><ref>{{harvnb|Collier|Balows|Sussman|1998|pp=11–21}}</ref>

; Regressive theory : Viruses may have once been small cells that [[parasitism|parasitised]] larger cells. Eventually, the genes they no longer needed for a parasitic way of life were lost. The bacteria ''[[Rickettsia]]'' and ''[[Chlamydia (bacterium)|Chlamydia]]'' are living cells that, like viruses, can reproduce only inside host cells. This lends credence to this theory, as their dependence on being parasites may have led to the loss of the genes that once allowed them to live on their own.<ref>{{harvnb|Collier|Balows|Sussman|1998|p=11}}</ref>

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=== Protein synthesis ===

[[File:~~Biological~~Cell ~~cell~~with Virus.~~svg~~png|thumb|upright=1.3|Diagram of a typical [[eukaryotic]] cell, showing subcellular components. [[Organelle]]s: (1) [[nucleolus]] (2) [[Cell nucleus|nucleus]] (3) [[ribosome]] (4) [[vesicle (biology)|vesicle]] (5) rough [[endoplasmic reticulum]] (ER) (6) [[Golgi apparatus]] (7) [[cytoskeleton]] (8) smooth ER (9) [[Mitochondrion|mitochondria]] (10) [[vacuole]] (11) [[cytoplasm]] (12) [[lysosome]] (13) [[centriole]]s within [[centrosome]] (14) a virus shown to approximate scale]]

Proteins are essential to life. Cells produce new protein molecules from [[amino acid]] building blocks based on information coded in DNA. Each type of protein is a specialist that usually only performs one function, so if a cell needs to do something new, it must make a new protein. Viruses force the cell to make new proteins that the cell does not need, but are needed for the virus to reproduce. [[Protein biosynthesis|Protein synthesis]] consists of two major steps: [[Transcription (genetics)|transcription]] and [[Translation (biology)|translation]].<ref name="pmid25648499">{{cite journal |vauthors=de Klerk E, 't Hoen PA |title=Alternative mRNA transcription, processing, and translation: insights from RNA sequencing |journal=Trends in Genetics |volume=31 |issue=3 |pages=128–139 |date=March 2015 |pmid=25648499 |doi=10.1016/j.tig.2015.01.001 }}</ref>

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[[File:HepC replication.png|thumb|Life-cycle of a typical virus (left to right); following infection of a cell by a single virus, hundreds of offspring are released.~~{{imagefact|date=December 2022}}~~]]

When a virus infects a cell, the virus forces it to make thousands more viruses. It does this by making the cell copy the virus's DNA or RNA, making viral proteins, which all assemble to form new virus particles.<ref>{{harvnb|Shors|2017|pp=6–13}}</ref>

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== Effects on the host cell ==

Viruses have an extensive range of structural and biochemical effects on the host cell.{{sfn | Oxford |Kellam|Collier| 2016 | p=34–36}}These are called ''[[cytopathic effect]]s''.{{sfn | Oxford |Kellam|Collier| 2016 | p=34}} Most virus infections eventually result in the death of the host cell. The causes of death include cell lysis (bursting), alterations to the cell's surface membrane and [[apoptosis]] (cell "suicide").<ref name="pmid28846635">{{cite journal |vauthors=Okamoto T, Suzuki T, Kusakabe S, Tokunaga M, Hirano J, Miyata Y, Matsuura Y |title=Regulation of Apoptosis during Flavivirus Infection |journal=Viruses |volume=9 |issue=9 |pages= 243|year= 2017 |pmid=28846635 |pmc=5618009 |doi=10.3390/v9090243|doi-access=free }}</ref> Often cell death is caused by cessation of its normal activity due to proteins produced by the virus, not all of which are components of the virus particle.<ref name="pmid18637511">{{cite ~~book~~journal ||vauthors= Alwine JC | title = ~~Human Cytomegalovirus | chapter =~~ Modulation of host cell stress responses by human cytomegalovirus | journal =Current ~~Curr.~~Topics ~~Top.~~in ~~Microbiol.~~Microbiology ~~Immunol.~~and |Immunology |volume = 325 | pages = ~~263–279~~263–79 | date = 2008 | pmid = 18637511 | doi = 10.1007/978-3-540-77349-8_15 ~~| series = Current Topics in Microbiology and Immunology | isbn = 978-3-540-77348-1~~ }}</ref>

Some viruses cause no apparent changes to the infected cell. Cells in which the virus is [[virus latency|latent]] (inactive) show few signs of infection and often function normally.<ref name="pmid18164651">{{cite journal | vauthors = Sinclair J | title = Human cytomegalovirus: Latency and reactivation in the myeloid lineage | journal = J. Clin. Virol. | volume = 41 | issue = 3 | pages = 180–185 | date = March 2008 | pmid = 18164651 | doi = 10.1016/j.jcv.2007.11.014 }}</ref> This causes persistent infections and the virus is often dormant for many months or years. This is often the case with [[herpes simplex|herpes viruses]].<ref name="pmid6326635">{{cite journal | vauthors = Jordan MC, Jordan GW, Stevens JG, Miller G | title = Latent herpesviruses of humans | journal = Ann. Intern. Med. | volume = 100 | issue = 6 | pages = 866–880 | date = June 1984 | pmid = 6326635 | doi = 10.7326/0003-4819-100-6-866 }}</ref><ref name="pmid12076064">{{cite journal | vauthors = Sissons JG, Bain M, Wills MR | s2cid = 24879226 | title = Latency and reactivation of human cytomegalovirus | journal = J. Infect. | volume = 44 | issue = 2 | pages = 73–77 | date = February 2002 | pmid = 12076064 | doi = 10.1053/jinf.2001.0948}}</ref>

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{{for|more examples of diseases caused by viruses|List of infectious diseases}}

Common human diseases caused by viruses include the [[common cold]], [[influenza]], [[chickenpox]] and [[cold sores]]. Serious diseases such as [[Ebola]] and [[AIDS]] are also caused by viruses.<ref>{{harvnb|Shors|2017|p=271}}</ref> Many viruses cause little or no disease and are said to be "benign". The more harmful viruses are described as [[virulence|virulent]].<ref>{{cite journal|vauthors =Berngruber TW, Froissart R, Choisy M, Gandon S|year= 2013|title = Evolution of Virulence in Emerging Epidemics|journal = PLOS Pathogens|volume= 9 |issue= 3|pages= e1003209|doi= 10.1371/journal.ppat.1003209|pmid= 23516359|pmc= 3597519|doi-access= free}}</ref>

Viruses cause different diseases depending on the types of cell that they infect.

Some viruses can cause lifelong or [[Chronic (medical)|chronic]] infections where the viruses continue to reproduce in the body despite the host's defence mechanisms.<ref>{{harvnb|Shors|2017|p=464}}</ref> This is common in hepatitis B virus and hepatitis C virus infections. People chronically infected with a virus are known as carriers. They serve as important reservoirs of the virus.<ref name="pmid31364248">{{cite journal |vauthors=Tanaka J, Akita T, Ko K, Miura Y, Satake M |title=Countermeasures against viral hepatitis B and C in Japan: An epidemiological point of view |journal=Hepatology Research |volume=49 |issue=9 |pages=990–1002 |date=September 2019 |pmid=31364248 |pmc=6852166 |doi=10.1111/hepr.13417 }}</ref><ref name="pmid32173241">{{cite journal |vauthors=Lai CC, Liu YH, Wang CY, Wang YH, Hsueh SC, Yen MY, Ko WC, Hsueh PR |title=Asymptomatic carrier state, acute respiratory disease, and pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): Facts and myths |journal=Journal of Microbiology, Immunology, and Infection = Wei Mian Yu Gan Ran Za Zhi |volume= 53|issue= 3|pages= 404–412|date=March 2020 |pmid=32173241 |doi=10.1016/j.jmii.2020.02.012 |pmc=7128959 }}</ref>

==== Endemic ====

If the proportion of carriers in a given population reaches a given threshold, a disease is said to be [[Endemic (epidemiology)|endemic]].{{sfn | Oxford |Kellam|Collier| 2016 | p=63}} Before the advent of vaccination, infections with viruses were common and outbreaks occurred regularly. In countries with a temperate climate, viral diseases are usually seasonal. [[Poliomyelitis]], caused by [[poliovirus]] often occurred in the summer months.<ref name="pmid29961515">{{cite journal |vauthors=Strand LK |title=The Terrible Summer of 1952 … When Polio Struck Our Family |journal=Seminars in Pediatric Neurology |volume=26 |pages=39–44 |date=July 2018 |pmid=29961515 |doi=10.1016/j.spen.2017.04.001 |s2cid=49640682 }}</ref> By contrast colds, influenza and rotavirus infections are usually a problem during the winter months.<ref name="pmid22958213">{{cite journal |vauthors=Moorthy M, Castronovo D, Abraham A, Bhattacharyya S, Gradus S, Gorski J, Naumov YN, Fefferman NH, Naumova EN |title=Deviations in influenza seasonality: odd coincidence or obscure consequence? |journal=Clinical Microbiology and Infection |volume=18 |issue=10 |pages=955–962 |date=October 2012 |pmid=22958213 |pmc=3442949 |doi=10.1111/j.1469-0691.2012.03959.x }}</ref><ref name="pmid25777068">{{cite journal |vauthors=Barril PA, Fumian TM, Prez VE, Gil PI, Martínez LC, Giordano MO, Masachessi G, Isa MB, Ferreyra LJ, Ré VE, Miagostovich M, Pavan JV, Nates SV |title=Rotavirus seasonality in urban sewage from Argentina: effect of meteorological variables on the viral load and the genetic diversity |journal=Environmental Research |volume=138 |pages=409–415 |date=April 2015 |pmid=25777068 |doi=10.1016/j.envres.2015.03.004 |bibcode=2015ER....138..409B |hdl=11336/61497 |hdl-access=free }}</ref> Other viruses, such as [[measles virus]], caused outbreaks regularly every third year.<ref name="pmid25444814">{{cite journal |vauthors=Durrheim DN, Crowcroft NS, Strebel PM |title=Measles – The epidemiology of elimination |journal=Vaccine |volume=32 |issue=51 |pages=6880–6883 |date=December 2014 |pmid=25444814 |doi=10.1016/j.vaccine.2014.10.061 |doi-access=free |hdl=1959.13/1299149 |hdl-access=free }}</ref> In developing countries, viruses that cause respiratory and enteric infections are common throughout the year. Viruses carried by insects are a common cause of diseases in these settings. [[Zika]] and [[dengue virus]]es for example are transmitted by the female Aedes mosquitoes, which bite humans particularly during the mosquitoes' breeding season.<ref name="pmid32103776">{{cite journal |vauthors=Mbanzulu KM, Mboera LE, Luzolo FK, Wumba R, Misinzo G, Kimera SI |title=Mosquito-borne viral diseases in the Democratic Republic of the Congo: a review |journal=Parasites & Vectors |volume=13 |issue=1 |pages=103 |date=February 2020 |pmid=32103776 |pmc=7045448 |doi=10.1186/s13071-020-3985-7 |doi-access=free }}</ref>

==== Pandemic and emergent ====

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[[Severe acute respiratory syndrome]] (SARS) and [[Middle East respiratory syndrome]] (MERS) are caused by new types of [[coronavirus]]es. Other coronaviruses are known to cause mild infections in humans,<ref name="pmid22094080">{{cite book |vauthors=Weiss SR, Leibowitz JL |title=Coronavirus pathogenesis |volume=81|pages=85–164 |year=2011 |pmid=22094080 |doi=10.1016/B978-0-12-385885-6.00009-2 |series=Advances in Virus Research |pmc=7149603 |isbn=978-0-12-385885-6}}</ref> so the virulence and rapid spread of SARS infections—that by July 2003 had caused around 8,000 cases and 800 deaths—was unexpected and most countries were not prepared.<ref name="pmid28475794">{{cite journal |vauthors=Wong AT, Chen H, Liu SH, Hsu EK, Luk KS, Lai CK, Chan RF, Tsang OT, Choi KW, Kwan YW, Tong AY, Cheng VC, Tsang DC |title=From SARS to Avian Influenza Preparedness in Hong Kong |journal=Clinical Infectious Diseases |volume=64 |issue=suppl_2 |pages=S98–S104 |date=May 2017 |pmid=28475794 |doi=10.1093/cid/cix123 |doi-access=free }}</ref>

A related coronavirus emerged in [[Wuhan]], China, in November 2019 and spread rapidly around the world. Thought to have originated in bats and subsequently named [[severe acute respiratory syndrome coronavirus 2]], infections with the virus cause a disease called [[COVID-19]], that varies in severity from mild to deadly,<ref name="WHOReport24Feb2020">{{cite report | title = Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) | date = 16–24 February 2020 | url = https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf | publisher = [[World Health Organization]] (WHO) | access-date = 21 March 2020}}</ref> and led to a [[COVID-19 pandemic|pandemic in 2020]].<ref name="pmid32143502">{{cite journal |vauthors=Ashour HM, Elkhatib WF, Rahman MM, Elshabrawy HA |title=Insights into the Recent 2019 Novel Coronavirus (SARS-CoV-2) in Light of Past Human Coronavirus Outbreaks |journal=Pathogens (Basel, Switzerland) |volume=9 |issue=3 |pages= 186|date=March 2020 |pmid=32143502 |doi=10.3390/pathogens9030186 |pmc=7157630 |doi-access=free }}</ref><ref name="pmid32093211">{{cite journal |vauthors=Deng SQ, Peng HJ |title=Characteristics of and Public Health Responses to the Coronavirus Disease 2019 Outbreak in China |journal=Journal of Clinical Medicine |volume=9 |issue=2 |pages= 575|date=February 2020 |pmid=32093211 |doi=10.3390/jcm9020575 |pmc=7074453 |doi-access=free }}</ref><ref name="pmid32109444">{{cite journal |vauthors=Han Q, Lin Q, Jin S, You L |title=Coronavirus 2019-nCoV: A brief perspective from the front line |journal=The Journal of Infection |volume= 80|issue= 4|pages= 373–377|date=February 2020 |pmid=32109444 |doi=10.1016/j.jinf.2020.02.010 |pmc=7102581 }}</ref> Restrictions unprecedented in peacetime were placed on international travel,<ref>{{Cite news|url=https://www.nytimes.com/article/coronavirus-travel-restrictions.html|title=Coronavirus Travel Restrictions, Across the Globe| vauthors = Londoño E, Ortiz A |work=The New York Times |date=16 March 2020|via=NYTimes.com}}</ref> and [[curfews]] imposed in several major cities worldwide.<ref>{{Cite web|url=http://www.cidrap.umn.edu/news-perspective/2020/03/us-takes-more-big-pandemic-response-steps-europe-covid-19-cases-soar|title=US takes more big pandemic response steps; Europe COVID-19 cases soar|website=CIDRAP|date=15 March 2020 }}</ref>

=== In plants ===

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==== Antiviral drugs ====

[[File:Guanosine~~-acyclovir-~~ aciclovir comparison.~~png~~svg|thumb|upright|The structure of the DNA base [[guanosine]] and the antiviral drug [[aciclovir]] which functions by mimicking it]]

Since the mid-1980s, the development of [[antiviral drug]]s has increased rapidly, mainly driven by the AIDS pandemic. Antiviral drugs are often [[nucleoside analogue]]s, which masquerade as DNA building blocks ([[nucleoside]]s). When the replication of virus DNA begins, some of the fake building blocks are used. This prevents DNA replication because the drugs lack the essential features that allow the formation of a DNA chain. When DNA production stops the virus can no longer reproduce.<ref>{{harvnb|Shors|2017|pp=514–515}}</ref> Examples of nucleoside analogues are [[aciclovir]] for [[Herpesviridae|herpes virus]] infections and [[lamivudine]] for HIV and [[hepatitis B virus]] infections. Aciclovir is one of the oldest and most frequently prescribed antiviral drugs.<ref>{{harvnb|Shors|2017|p=514}}</ref>

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== Role in ecology ==

Viruses are the most abundant biological entity in aquatic environments;<ref name="pmid16984643">{{cite journal | vauthors = Koonin EV, Senkevich TG, Dolja VV | title = The ancient Virus World and evolution of cells | journal = Biol. Direct | volume = 1 | page= 29 | date = September 2006 | pmid = 16984643 | pmc = 1594570 | doi = 10.1186/1745-6150-1-29 | doi-access = free }}</ref> one teaspoon of seawater contains about ten million viruses,<ref name="pmid31749771">{{cite journal |vauthors=Dávila-Ramos S, Castelán-Sánchez HG, Martínez-Ávila L, Sánchez-Carbente MD, Peralta R, Hernández-Mendoza A, Dobson AD, Gonzalez RA, Pastor N, Batista-García RA |title=A Review on Viral Metagenomics in Extreme Environments |journal=Frontiers in Microbiology |volume=10 |pages=2403 |date=2019 |pmid=31749771 |pmc=6842933 |doi=10.3389/fmicb.2019.02403 |doi-access=free }}</ref> and they are essential to the regulation of saltwater and freshwater ecosystems.<ref>{{harvnb|Shors|2017|p=5}}</ref> Most are bacteriophages,<ref name="pmid29867096">{{cite journal |vauthors=Breitbart M, Bonnain C, Malki K, Sawaya NA |s2cid=46927784 |title=Phage puppet masters of the marine microbial realm |journal=Nature Microbiology |volume=3 |issue=7 |pages=754–766 |date=July 2018 |pmid=29867096 |doi=10.1038/s41564-018-0166-y }}</ref> which are harmless to plants and animals. They infect and destroy the bacteria in aquatic microbial communities and this is the most important mechanism of recycling carbon in the marine environment. The organic molecules released from the bacterial cells by the viruses stimulate fresh bacterial and algal growth.<ref>{{harvnb|Shors|2017|pp=25–26}}</ref>

Microorganisms constitute more than 90% of the biomass in the sea. It is estimated that viruses kill approximately 20% of this biomass each day and that there are fifteen times as many viruses in the oceans as there are bacteria and archaea. They are mainly responsible for the rapid destruction of harmful [[algal bloom]]s,<ref name="pmid16163346">{{cite journal | vauthors = Suttle CA | title = Viruses in the sea | journal = Nature | volume = 437 | issue = 7057 | pages = 356–361 | date = September 2005 | pmid = 16163346 | doi = 10.1038/nature04160 |bibcode = 2005Natur.437..356S | s2cid = 4370363 }}</ref> which often kill other marine life.<ref>{{cite web|url=https://www.cdc.gov/hab/redtide/|title=Harmful Algal Blooms: Red Tide: Home | CDC HSB|publisher=www.cdc.gov|access-date=23 August 2009}}</ref>

The number of viruses in the oceans decreases further offshore and deeper into the water, where there are fewer host organisms.<ref name="pmid17853907">{{cite journal | vauthors = Suttle CA | title = Marine viruses – major players in the global ecosystem | journal = Nat. Rev. Microbiol. | volume = 5 | issue = 10 | pages = 801–812 | date = October 2007 | pmid = 17853907 | doi = 10.1038/nrmicro1750 | s2cid = 4658457 }}</ref>

Their effects are far-reaching; by increasing the amount of respiration in the oceans, viruses are indirectly responsible for reducing the amount of carbon dioxide in the atmosphere by approximately 3 [[gigatonne]]s of carbon per year.<ref name="pmid17853907" />

Marine mammals are also susceptible to viral infections. In 1988 and 2002, thousands of harbour seals were killed in Europe by [[phocine distemper virus]].<ref>{{cite journal | vauthors = Hall A, Jepson P, Goodman S, Harkonen T | title= Phocine distemper virus in the North and European Seas – Data and models, nature and nurture | journal= Biological Conservation | volume= 131 | issue= 2 | pages= 221–229 | year= 2006 |doi = 10.1016/j.biocon.2006.04.008 | bibcode= 2006BCons.131..221H }}</ref> Many other viruses, including caliciviruses, herpesviruses, adenoviruses and parvoviruses, circulate in marine mammal populations.<ref name="pmid17853907" />

Viruses can also serve as an alternative food source for microorganisms which engage in [[Virovore|virovory]], supplying nucleic acids, nitrogen, and phosphorus through their consumption.<ref name="New Virovore">{{Cite journal |last1=DeLong |first1=John P. |last2=Van Etten |first2=James L. |last3=Al-Ameeli |first3=Zeina |last4=Agarkova |first4=Irina V. |last5=Dunigan |first5=David D. |date=2023-01-03 |title=The consumption of viruses returns energy to food chains |journal=Proceedings of the National Academy of Sciences |language=en |volume=120 |issue=1 |pages=e2215000120 |doi=10.1073/pnas.2215000120 |pmid=36574690 |pmc=9910503 |bibcode=2023PNAS..12015000D |issn=0027-8424}}</ref><ref name="First Virovore">{{cite news |last1=Irving |first1=Michael |title=First "virovore" discovered: An organism that eats viruses |url=https://newatlas.com/science/first-virovore-eats-viruses/ |access-date=29 December 2022 |publisher=New Atlas |date=28 December 2022 |archive-url=https://web.archive.org/web/20221229023549/https://newatlas.com/science/first-virovore-eats-viruses/ |archive-date=29 December 2022}}</ref>

== See also ==

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=== Bibliography ===

*{{cite book | editor-last = Collier | editor-first =Leslie |editor-last2=Balows| editor-first2 =Albert | editor-last3 =Sussman | editor-first3 =Max ~~| name-list-style = vanc~~ | title = Topley & Wilson's Microbiology and Microbial Infections | publisher = Arnold | year = 1998 | isbn = 0-340-66316-2 |edition=9th|volume=1, ''Virology''}}

*{{cite book | last1=Oxford

title=Human Virology | publisher=Oxford University Press | publication-place=Oxford | year=2016 | isbn=978-0-19-871468-2 | oclc=968152575}}

*{{cite book | last = Shors | first = Teri ~~| name-list-style = vanc~~ | title = Understanding Viruses | publisher = Jones and Bartlett Publishers | year = 2017 | isbn = 978-1284025927 }}