Viral encephalitis pathophysiology

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

Overview

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.

Pathophysiology

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:

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

Arboviruses

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:

• Penetration of cerebrovasculature following endothelial cell infection
• Diapedesis of infected leukocytes
• Penetration of choroid plexus

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Encephalitis Lethargica

Main article: Encephalitis lethargica

Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928. 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.

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).