Encephalitis is an uncommon but serious condition in which the brain becomes inflamed (swollen).
It can be life threatening and requires urgent treatment in hospital.
Anyone can be affected, but the very young and very old are most at risk.
More serious symptoms come on over hours, days or weeks, including:
Dial 999 for an ambulance immediately if you or someone else has these more serious symptoms.
It's not always clear what causes encephalitis, but it can be caused by:
You cannot catch encephalitis from someone else.
Encephalitis needs to be treated in a hospital. The earlier treatment is started, the more successful it's likely to be.
Treatment depends on the underlying cause, but may include:
How long someone with encephalitis needs to stay in hospital can range from a few days to several weeks or even months.
Some people eventually make a full recovery from encephalitis, although this can be a long and frustrating process.
Many people never make a full recovery and are left with long-term problems caused by damage to their brain.
Common complications include:
These problems can have a significant impact on the life of the affected person, as well as their family and friends.
But help and support is available.
It's not always possible to prevent encephalitis, but some of the infections that cause it can be prevented with vaccinations.
These include the:
Speak to a GP surgery if you're not sure whether your vaccinations are up to date, or you're planning to travel abroad and do not know if you need any vaccinations.