Encephalitis is an uncommon but serious condition that causes inflammation of the brain. 

Encephalitis usually begins with flu-like symptoms, such as a high temperature, a 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. In these circumstances, dial 999 immediately and request an ambulance.

Read more about the symptoms of encephalitis.

Why does encephalitis happen?

There are several different types of encephalitis that have different causes. The most common 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 sometimes 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 the result of a condition such as HIV, though in some cases there is 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.

How is encephalitis treated?

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 from attacking healthy tissue)

Read more about diagnosing encephalitis and treating encephalitis.


Some people make a full recovery from encephalitis. But for many, encephalitis can lead to permanent brain damage and complications, including:

  • memory loss
  • epilepsy, a condition that causes repeated seizures
  • 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 is 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 encephalitis is to make sure you receive the MMR vaccine (for measles, mumps and rubella).

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

Other vaccinations

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

The animals that cause these types of encephalitis are rare in the UK, but more widespread in certain parts of the world. Generally, rabies is 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.

It is a good idea to discuss these vaccinations with your GP before travelling.

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

Brain scans are often used to diagnose encephalitis 

Who is affected?

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

People of all ages and both sexes can be affected by encephalitis, but the very young and the very old are most at risk because their immune system (the body's natural defence against infection and illness) tends to be weaker.

How to prevent germs from spreading

Cleaning and good hygiene tips to help reduce the number of germs in your home

Page last reviewed: 29/11/2012

Next review due: 29/11/2014