Viral encephalitis pathophysiology

Template:Encephalitis Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. Sometimes, encephalitis can result from a bacterial infection, such as bacterial meningitis, or it may be a complication of other infectious diseases like rabies (viral) or syphilis (bacterial). Certain 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 death.

Pathophysiology

Encephalitis is a rare condition. It occurs more often in the first year of life and decreases with age. The very young and the elderly are more likely to have a severe case. Encephalitis is most often caused by a viral infection. The virus causes inflammation of brain tissue. The brain tissue swells (cerebral edema), which may destroy nerve cells, cause bleeding in the brain (intracerebral hemorrhage), and brain damage. Many types of viruses may cause it. Exposure to viruses can occur through:

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

Different viruses will occur in different locations. Many cases will tend to cluster in a certain season. Encephalitis caused by the herpes simplex virus is the leading cause of more severe cases in all ages, including newborns. A number of viruses for which there is now a vaccine may also cause encephalitis.

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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).