Viral encephalitis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]


Encephalitis is an acute inflammation of the brain. Encephalitis is caused by a viral or bacterial infection, with viral being more common. Parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Brain damage occurs as the inflamed brain pushes against the skull, and can lead to subsequent mortality.


Encephalitis is most often caused by a viral infection, which causes inflammation of brain tissue. The brain tissue swells (cerebral edema), which may destroy nerve cells, cause intracerebral hemorrhage, and brain damage. Viruses are usually transmitted via the following routes to the human host:[1]

  • Inhaling respiratory droplets from an infected person
  • Contaminated food or drink
  • Mosquito, tick, and other insect bites
  • Skin contact with an infected person


Following transmission/ingestion, an arbovirus uses the bite site to invade the dendritic cells. The virus replicates within dendrites and macrophages in lymph nodes, resulting in spread to the central nervous system. The exact pathogenesis of encephalitis is not fully understood. It is thought that encephalitis is the result of either:[1]

On microscopic histopathological analysis, the peripheral cuffing of lymphocytes surrounding blood vessels within the brain is the characteristic finding of encephalitis. The following video demonstrates an example of encephalitis:[2] {{#ev:youtube|uOgS4Vk5qBY}}

Encephalitis Lethargica

Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928.[3] There have only been a small number of isolated cases since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be either a bacterial agent or an autoimmune response following infection.[4]

Limbic System Encephalitis

In a small number of cases, called limbic encephalitis, the pathogens responsible for encephalitis attack primarily the limbic system (a collection of structures at the base of the brain responsible for basic autonomic functions).


  1. 1.0 1.1 Mandell, Gerald L.; Bennett, John E. (John Eugene); Dolin, Raphael. (2010). Mandell, Douglas, and Bennett's principles and practice of infectious disease. Philadelphia, PA: Churchill Livingstone/Elsevier. ISBN 0-443-06839-9.
  2. Michael BD, Griffiths MJ, Granerod J, Brown D, Davies NW, Borrow R; et al. (2016). "Characteristic Cytokine and Chemokine Profiles in Encephalitis of Infectious, Immune-Mediated, and Unknown Aetiology". PLoS One. 11 (1): e0146288. doi:10.1371/journal.pone.0146288. PMID 26808276.
  3. Reid AH, McCall S, Henry JM, Taubenberger JK (2001). "Experimenting on the past: the enigma of von Economo's encephalitis lethargica". J. Neuropathol. Exp. Neurol. 60 (7): 663–70. PMID 11444794.
  4. Dale RC, Church AJ, Surtees RA; et al. (2004). "Encephalitis lethargica syndrome: 20 new cases and evidence of basal ganglia autoimmunity". Brain. 127 (Pt 1): 21–33. doi:10.1093/brain/awh008. PMID 14570817.

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