Editing Viral meningitis (section)

==Mechanism==
[[File:Meningitis.webm|thumb|Meningitis]]
Viral Meningitis is mostly caused by an [[infectious agent]] that has colonized somewhere in its [[Host organism|host]].<ref name=":0">{{Cite journal|date=2017-11-29|title=Viral Meningitis: Background, Pathophysiology, Etiology|url=https://emedicine.medscape.com/article/1168529-overview}}</ref> People who are already in an immunocompromised state are at the highest risk of pathogen entry.<ref name=":3">{{Cite web|url=http://www.pathophys.org/meningitis/|title=Meningitis {{!}} McMaster Pathophysiology Review|website=www.pathophys.org|language=en-US|access-date=2017-12-12}}</ref> Some of the most common examples of immunocompromised individuals include those with HIV, cancer, diabetes, malnutrition, certain genetic disorders, and patients on chemotherapy.<ref name=":3" /> Potential sites for this include the skin, [[respiratory tract]], [[gastrointestinal tract]], [[nasopharynx]], and [[genitourinary tract]]. The organism invades the [[submucosa]] at these sites by invading host defenses, such as local immunity, physical barriers, and [[phagocytes]] or [[macrophages]].<ref name=":0" /> After pathogen invasion, the immune system is activated.<ref name=":3"/> An [[infectious agent]] can enter the [[central nervous system]] and cause meningeal disease via invading the bloodstream, a retrograde neuronal pathway, or by direct contiguous spread.<ref>{{Cite book|chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK8423/|title=Medical Microbiology|last=Klimpel|first=Gary R.|date=1996|publisher=University of Texas Medical Branch at Galveston|isbn=978-0963117212|editor-last=Baron|editor-first=Samuel|edition=4th|location=Galveston (TX)|pmid=21413332|chapter=Immune Defenses}}</ref> Immune cells and damaged [[endothelial cells]] release [[matrix metalloproteinases]] (MMPs), [[cytokines]], and [[nitric oxide]]. MMPs and NO induce [[vasodilation]] in the [[cerebral vasculature]]. Cytokines induce [[capillary]] wall changes in the [[blood brain barrier]], which leads to expression of more [[leukocyte]] receptors, thus increasing white blood cell binding and [[extravasation]].<ref name=":3" />

The barrier that the [[meninges]] create between the [[brain]] and the [[bloodstream]] are what normally protect the brain from the body's [[immune system]]. Damage to the [[meninges]] and [[endothelial cells]] increases [[cytotoxic]] [[reactive oxygen species]] production, which damages pathogens as well as nearby cells.<ref name=":3" /> In [[meningitis]], the barrier is disrupted, so once viruses have entered the brain, they are isolated from the immune system and can spread.<ref>{{cite journal | vauthors = Chadwick DR | title = Viral meningitis | journal = British Medical Bulletin | volume = 75–76 | issue = 1 | pages = 1–14 | date = 2005-01-01 | pmid = 16474042 | doi = 10.1093/bmb/ldh057 | doi-access = free }}</ref> This leads to elevated [[intracranial]] pressure, cerebral [[edema]], meningeal irritation, and neuronal death.<ref name=":3" />