Editing Virulence (section)

{{Short description|Severity of disease pathogens on its host}}
{{For|the academic journal|Virulence (journal)}}

'''Virulence''' is a [[pathogen]]'s or [[microorganism]]'s ability to cause damage to a host.

In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its [[host (biology)|host]].<ref name="Pirofski2012">{{cite journal|vauthors=Pirofski LA, Casadevall A|title=Q and A: What is a pathogen? A question that begs the point|journal=BMC Biology|volume=10|pages=6|year=2012|pmid=22293325|pmc=3269390|doi=10.1186/1741-7007-10-6 |doi-access=free }}</ref> The [[Pathogen#Pathogenicity|pathogenicity]] of an organism—its ability to cause [[disease]]—is determined by its [[virulence factor]]s.<ref>{{Cite web |url=http://mesh.kib.ki.se/swemesh/show.swemeshtree.cfm?Mesh_No=G06.930&tool=karolinska |title=MeSH - Medical Subject Headings, Karolinska Institute, 13 April 2010 |access-date=13 April 2010 |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303190453/http://mesh.kib.ki.se/swemesh/show.swemeshtree.cfm?Mesh_No=G06.930&tool=karolinska |url-status=dead }}</ref><ref>{{cite web|last1=Biology Online|title=Virulence|url=https://www.biologyonline.com/dictionary/virulence|website=Biology Online|date=7 October 2019}}</ref> In the specific context of [[Gene-for-gene relationship|gene for gene]] systems, often in plants, virulence refers to a pathogen's ability to infect a resistant host.<ref>{{Cite journal|last1=Thrall|first1=Peter H.|last2=Burdon|first2=Jeremy J.|year=2003|title=Evolution of Virulence in a Plant Host-Pathogen Metapopulation|journal=Science|language=en|volume=299|issue=5613|pages=1735–7|doi=10.1126/science.1080070|issn=0036-8075|pmid=12637745|bibcode=2003Sci...299.1735T|s2cid=6894315}}</ref> Virulence can also be transferred using a [[plasmid]].

The [[noun]] ''virulence'' ([[Latin]] noun {{lang|la|virulentia}}) derives from the [[adjective]] ''virulent'', meaning disease severity.<ref name="oxford">{{OED|virulent|id=223857}}</ref> The word ''virulent'' derives from the Latin word ''virulentus'', meaning "a poisoned wound" or "full of poison".<ref name="oxford" /><ref>{{Cite book|title=A Latin Dictionary |first1=Charlton T. |last1=Lewis |first2=Charles |last2=Short |chapter-url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aentry%3D%2351111 |chapter=vīrŭlentus |title-link=A Latin Dictionary |access-date=2023-01-02}}</ref> The term ''virulence'' does not only apply to viruses.

From an [[ecology|ecological]] standpoint, virulence is the loss of [[fitness (biology)|fitness]] induced by a parasite upon its host. Virulence can be understood in terms of [[Proximate and ultimate causation|proximate causes]]—those specific traits of the pathogen that help make the host ill—and [[Proximate and ultimate causation|ultimate causes]]—the evolutionary pressures that lead to virulent traits occurring in a pathogen strain.<ref>{{Cite web|title=Plant disease &#124; Importance, Types, Transmission, & Control &#124; Britannica|url=https://www.britannica.com/science/plant-disease|access-date=2023-01-02|website=www.britannica.com|language=en}}</ref>