Introduction to viruses: Difference between revisions - Wikipedia
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Line 100: {{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 }}</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 }}</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 ==== Line 173: == 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> Line 182: 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 }}</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 | == See also == | |||