Introduction to viruses: Difference between revisions

Revision as of 13:07, 11 July 2025

Latest revision as of 05:07, 12 July 2025

(2 intermediate revisions by one other user not shown)

Line 25:

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" ({{langx|la|text= [[contagium vivum fluidum]]}})—or a "soluble living germ" because he could not find any germ-like particles.<ref>{{sfn|Howley|Knipe|Enquist|2023|p=4}}</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>

Line 106:

==== 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 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 |pagesarticle-number=103 |date=February 2020 |pmid=32103776 |pmc=7045448 |doi=10.1186/s13071-020-3985-7 |doi-access=free }}</ref>

==== Pandemic and emergent ====

[[File:SIV primates.jpg|right|400px|thumb|Left to right: the [[African green monkey]], source of [[Simian immunodeficiency virus|SIV]]; the [[sooty mangabey]], source of [[HIV-2]]; and the [[Common chimpanzee|chimpanzee]], source of [[HIV-1]]]]

[[File:Orgin and evolution of SARS.jpg|thumb|Origin and evolution of (A) SARS-CoV, (B) MERS-CoV, and (C) SARS-CoV-2 in different hosts. All the viruses came from bats as coronavirus-related viruses before mutating and adapting to intermediate hosts and then to humans and causing the diseases [[SARS]], [[MERS]] and [[COVID-19]]. (<small>Adapted from Ashour et al. (2020)</small> <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>)]]

Although viral [[pandemic]]s are rare events, HIV—which evolved from viruses found in monkeys and chimpanzees—has been pandemic since at least the 1980s.<ref name="pmid29460740">{{cite journal |vauthors=Eisinger RW, Fauci AS |title=Ending the HIV/AIDS Pandemic1 |journal=Emerging Infectious Diseases |volume=24 |issue=3 |pages=413–416 |date=March 2018 |pmid=29460740 |pmc=5823353 |doi=10.3201/eid2403.171797 }}</ref> During the 20th century there were four pandemics caused by influenza virus and those that occurred in [[Spanish flu|1918]], [[1957–1958 influenza pandemic|1957]] and [[Hong Kong flu|1968]] were severe.<ref name="pmid30180422">{{cite journal |vauthors=Qin Y, Zhao MJ, Tan YY, Li XQ, Zheng JD, Peng ZB, Feng LZ |title=[History of influenza pandemics in China during the past century] |language=zh |journal=Zhonghua Liu Xing Bing Xue Za Zhi = Zhonghua Liuxingbingxue Zazhi |volume=39 |issue=8 |pages=1028–1031 |date=August 2018 |doi=10.3760/cma.j.issn.0254-6450.2018.08.003 |doi-broken-date=201 JuneJuly 2025 |pmid=30180422 }}</ref> Before its eradication, smallpox was a cause of pandemics for more than 3,000 years.<ref name="pmid26060873">{{cite journal |vauthors=Nishiyama Y, Matsukuma S, Matsumura T, Kanatani Y, Saito T |title=Preparedness for a smallpox pandemic in Japan: public health perspectives |journal=Disaster Medicine and Public Health Preparedness |volume=9 |issue=2 |pages=220–223 |date=April 2015 |pmid=26060873 |doi=10.1017/dmp.2014.157 |s2cid=37149836 }}</ref> Throughout history, human migration has aided the spread of pandemic infections; first by sea and in modern times also by air.<ref name="pmid30878442">{{cite journal |vauthors=Houghton F |title=Geography, global pandemics & air travel: Faster, fuller, further & more frequent |journal=Journal of Infection and Public Health |volume=12 |issue=3 |pages=448–449 |date=2019 |pmid=30878442 |doi=10.1016/j.jiph.2019.02.020 |pmc=7129534 }}</ref>

With the exception of smallpox, most pandemics are caused by newly evolved viruses. These [[Emergent virus|"emergent"]] viruses are usually mutants of less harmful viruses that have circulated previously either in humans or in other animals.<ref>{{Cite web|url=https://virologyj.biomedcentral.com/articles/sections/emerging-viruses|title=Virology Journal|website=Virology Journal}}</ref>

Line 197:

{{Refbegin}}

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

* {{cite book | lastlast1=Howley | firstfirst1=Peter M. | last2=Knipe | first2=David M. | last3=Enquist | first3=Lynn W. | title=Fields Virology: Fundamentals | publisher=LWW | publication-place=Philadelphia | date=2023-09-25 | isbn=978-1-9751-1251-6}}

*{{cite book | last1=Oxford

| first1=John |last2=Kellam|first2=Paul|last3=Collier|first3=Leslie|