Encephalitis is a rare but serious condition that causes inflammation of the brain.

It usually begins with flu-like symptoms, such as a high temperature, headache and joint pain.

More serious symptoms may then develop over the next few hours or days, including:

  • changes in mental state, such as confusion, drowsiness or disorientation
  • seizures (fits)
  • changes in personality and behaviour

Flu-like symptoms that rapidly get worse and affect mental state should be treated as a medical emergency. Dial 999 immediately to request an ambulance.

Read more about the symptoms of encephalitis.

What causes encephalitis?

There are several different types of encephalitis and each type has a different cause. The most common types of encephalitis are:

  • infectious  inflammation occurs as a direct result of an infection, which is often viral
  • post-infectious  inflammation is caused by the immune system reacting to a previous infection, and can occur days, weeks or months after the initial infection
  • autoimmune  inflammation is caused by the immune system reacting to a non-infectious cause, such as a tumour  
  • chronic  inflammation develops slowly over many months and can be due to a condition such as HIV; in some cases, there's no obvious cause

There are also several types of encephalitis spread by mosquitoes, such as Japanese encephalitis, and ticks, such as tick-borne encephalitis. Encephalitis can also be caused by rabies.

Read more about the causes of encephalitis.

In the UK, all types of encephalitis are relatively rare. The Encephalitis Society estimates that there are 4,000 case of encephalitis in the UK each year.

Anyone can be affected by encephalitis, but the very young and the very old are most at risk, because their immune systems tend to be weaker.

Treating encephalitis

Encephalitis needs urgent treatment, usually in a hospital intensive care unit (ICU). The earlier it's diagnosed, the more successful treatment is.

Treatment depends on the type of encephalitis you have, but may include:

  • anti-viral medication
  • steroid injections
  • immunosuppressants (medicines that stop the immune system attacking healthy tissue)

Read more about diagnosing encephalitis and treating encephalitis.


Some people make a full recovery after having encephalitis. However, for many it can lead to permanent brain damage and complications, including:

  • memory loss 
  • epilepsy
  • personality and behavioural changes
  • problems with attention, concentration, planning and problem solving  
  • fatigue (extreme tiredness)

Overall, about 10% of encephalitis cases are fatal.

Read more about the complications of encephalitis.

Preventing encephalitis

It's not always possible to prevent encephalitis. This is because it can be a rare complication of a relatively common infection.

The most effective way to reduce your risk of getting encephalitis is to ensure you have the MMR vaccine (for measles, mumps and rubella).

Practicing good hygiene for example, regularly washing your hands with soap and warm water can help to reduce your risk of developing common infections.

Other vaccinations

Vaccinations are also available for Japanese encephalitis, tick-borne encephalitis and encephalitis caused by rabies.

These types of encephalitis are rare in the UK, but more widespread in certain parts of the world. For example, rabies tends to be more common in Africa, Japanese encephalitis is more common in Asia, and the risk areas for tick-borne encephalitis are the forests of central, eastern and northern Europe.

You should discuss these specific vaccinations with your GP before travelling.

Read more about the Japanese encephalitis vaccination, preventing tick-borne encephalitis and the rabies vaccination.

Page last reviewed: 16/12/2014

Next review due: 16/12/2016