What is encephalitis?

Encephalitis is an inflammation of the brain, developed as a result of infection (usually viral) OR when the immune system attacks the tissue of the brain by mistake (known as post-infectious encephalitis).

Infection can involve one area of the brain (focal) or many scattered areas (diffuse).

Children who are under seven years of the age, and older adults, over the age of 55, are particularly vulnerable to infection.

In England, the most common cause of encephalitis is the herpes simplex virus (HSV).


What are the signs and symptoms?

Encephalitis usually begins with flu-like symptoms:

  • headaches
  • malaise

More serious symptoms then follow, usually over the space of a few hours, or days. These include:

  • high temperature (fever) of 38 ºC (100.4ºF) or above
  • nausea
  • vomiting
  • changes in mental state i.e. confusion
  • drowsiness or disorientation
  • seizures (fits)
  • dislike of bright lights (photophobia)
  • inability to speak
  • inability to control physical movements
  • stiff neck
  • uncharacteristic behaviour e.g. being unusually aggressive


There are long-term complications that can develop as a result of having encephalitis:

  • memory problems
  • personality and behavioural changes
  • problems with speech and language (aphasia)
  • epilepsy


What is encephalitis?
Signs & Symptoms
Prevention & Treatment
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