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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.

Encephalitis usually starts off with flu-like symptoms, such as a high temperature and headache.

More serious symptoms come on over hours, days or weeks, including:

• confusion or disorientation
• seizures or fits
• changes in personality and behaviour
• difficulty speaking
• weakness or loss of movement in some parts of the body
• loss of consciousness

Dial 999 for an ambulance immediately if you or someone else has these serious symptoms.

It's not always clear what causes encephalitis, but it can be caused by:

• viral infections – very rarely, encephalitis may be caused by the common viruses that causes cold sores (herpes simplex) or chickenpox (herpes varicella) spreading to the brain
• a problem with the immune system, the body's defence against infection – sometimes something goes wrong with the immune system and it mistakenly attacks the brain, causing it to become inflamed
• bacterial or fungal infections – these are much rarer causes of encephalitis than viral infections

Some types of encephalitis are spread by mosquitoes (such as Japanese encephalitis), ticks (such as tick-borne encephalitis) and mammals (such as rabies).

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:

• antiviral medicines
• steroid injections
• treatments to help control the immune system
• antibiotics or antifungal medicines
• painkillers to reduce discomfort or a high temperature
• medicine to control seizures or fits
• support with breathing, such as oxygen through a face mask or a breathing machine (ventilator)

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:

• memory loss (amnesia)
• frequent seizures or fits
• personality and behavioural changes
• problems with attention, concentration, planning and problem solving
• persistent tiredness

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:

• measles, mumps and rubella (MMR) vaccine – a routine vaccination offered to all children in England
• Japanese encephalitis vaccine – recommended for travellers to at-risk areas, such as parts of Asia
• tick-borne encephalitis vaccine – recommended for travellers to certain parts of Europe (but not the UK) and Asia
• rabies vaccination – recommended for travellers to at-risk where access to medical care is likely to be limited. Find out about rabies risks in terrestrial animals by country on GOV.UK.

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.