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.

Symptoms of encephalitis

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

More serious symptoms develop over hours, days or weeks, including:

  • confusion or disorientation
  • seizures (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 more serious symptoms.

Causes of encephalitis

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 can't catch encephalitis from someone else.

Treatments for encephalitis

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 medication
  • steroid injections
  • treatments to help control the immune system
  • antibiotics or antifungal medication
  • painkillers to reduce discomfort or a fever
  • medication 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.

Recovering from encephalitis

Some people will 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 due to damage to their brain.

Common complications include:

  • memory loss
  • frequent seizures
  • 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.

Preventing encephalitis

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 your GP if you're not sure whether your vaccinations are up to date, or you're planning to travel abroad and don't know if you need any vaccinations.


Symptoms of encephalitis may be mild to begin with, but can become more serious over hours or days.

Occasionally the symptoms may develop gradually over several weeks or even months.

Early symptoms

The first symptoms of encephalitis can be similar to flu, such as:

  • a high temperature
  • a headache
  • feeling and being sick
  • aching muscles and joints

Some people may also have a spotty or blistery rash on their skin.

But these early symptoms don't always appear and sometimes the first signs of encephalitis may be the more serious symptoms listed below.

Serious symptoms

More severe symptoms develop when the brain is affected, such as:

  • confusion or disorientation
  • drowsiness
  • seizures (fits)
  • changes in personality and behaviour, such as feeling very agitated
  • difficulty speaking
  • weakness or loss of movement in some parts of the body
  • seeing and hearing things that aren't there (hallucinations)
  • loss of feeling in certain parts of the body
  • uncontrollable eye movements, such as side-to-side eye movement
  • eyesight problems
  • loss of consciousness

There may also be symptoms of meningitis, such as a severe headache, sensitivity to bright lights, a stiff neck and a spotty rash that doesn't fade when a glass is pressed against it.

When to get medical advice

Dial 999 immediately to request an ambulance if you or someone else has serious symptoms of encephalitis.

It's a medical emergency that needs to be seen in hospital as soon as possible.

Read about how encephalitis is diagnosed and how encephalitis is treated.

Who can get it

It's not always clear what causes encephalitis. When a cause is found, it's usually an infection or a problem with the immune system (the body's natural defences).


Encephalitis can happen if an infection spreads to the brain.

Many of the infections associated with the condition are quite common and are usually mild. Encephalitis only happens in rare cases.

The condition is most often due to a virus, such as:

Encephalitis caused by a virus is known as "viral encephalitis". In rare cases, encephalitis is caused by bacteria, fungi or parasites.

You can catch these infections from someone else, but encephalitis itself isn't spread from person to person.

Problems with the immune system

The immune system protects the body from illness and infection. When germs enter the body, the immune system attacks them to stop them causing a serious infection.

But very rarely something goes wrong with the immune system and it mistakenly attacks the brain, causing encephalitis.

This can be triggered by:

  • a previous infection in another part of the body (which usually occurs a few weeks earlier)
  • a non-cancerous or cancerous growth (tumour) somewhere in the body
  • a vaccination (this is very rare and the benefits of being vaccinated far outweigh the risk of encephalitis)
  • an unknown cause

Encephalitis due to a reaction to a previous infection is known as "post-infectious encephalitis". If it's caused by a tumour or the cause is unknown, it's called "autoimmune encephalitis".


The symptoms of encephalitis can have a number of possible causes, so several tests may be needed to diagnose it.

Brain scans

A scan of the brain can help show whether you have encephalitis or another problem such as a stroke, brain tumour or brain aneurysm (a swelling in an artery).

The two main types of scan used are:

Lumbar puncture

lumbar puncture is a procedure to remove some fluid from around the spinal cord (the nerves running up the spine) so it can be checked for signs of encephalitis.

For the procedure:

  • you lie on one side and bring your knees up towards your chin
  • local anaesthetic is used to numb your lower back
  • a needle is inserted into the lower part of your spine and a sample of fluid is removed

The sample will be checked for signs of infection or a problem with your immune system, which are the main causes of encephalitis.

Other tests

Other tests include:

  • an electroencephalogram (EEG) – small electrodes are placed on your scalp, which pick up the electrical signals from your brain and show abnormal brain activity
  • tests of your blood, urine or other bodily fluids to check for an infection


Encephalitis needs to be treated urgently. Treatment involves tackling the underlying cause, relieving symptoms and supporting bodily functions.

It's treated in hospital – usually in an intensive care unit (ICU), which is for people who are very ill and need extra care.

How long someone with encephalitis needs to stay in hospital can range from a few days to several weeks or even months.

This depends on how well treatment works and if any complications of encephalitis occur.

Treating the cause

If a cause of encephalitis is found, treatment to deal with this will start immediately.

Possible treatments include:

  • antiviral medication – used if encephalitis is caused by the herpes simplex or chickenpox viruses; it's usually given into a vein three times a day for two to three weeks
  • steroid injections – used if encephalitis is caused by a problem with the immune system and sometimes in cases linked to the chickenpox virus; treatment is usually for a few days
  • immunoglobulin therapy – medication that helps control the immune system, which may be needed if steroids don't help
  • plasmapheresis – a procedure which removes the substances that are attacking the brain from the blood, which may be needed if immunoglobulin therapy doesn't help
  • surgery to remove abnormal growths (tumours) – done if encephalitis was triggered by a tumour somewhere in the body
  • antibiotics or antifungal medication – used if encephalitis is caused by a bacterial or antifungal infection

If there's no treatment for the underlying cause, treatment is given to support the body, relieve symptoms, and allow the best chance of recovery (see below).

Other treatments

Encephalitis puts a lot of strain on the body and can cause a range of unpleasant symptoms.

Most people need treatment to relieve these symptoms and to support certain bodily functions until they're feeling better.

This may involve:

  • fluids given into a vein to prevent dehydration
  • painkillers to reduce discomfort or a fever
  • medication to control seizures (fits)
  • medication to help the person relax if they're very agitated
  • oxygen given through a face mask to support the lungs – sometimes a machine called a ventilator may be used to control breathing
  • medication to prevent a build-up of pressure inside the skull

Occasionally, surgery to remove a small piece of the skull may be needed if the pressure inside increases and medication isn't helping.


Encephalitis is a serious condition and, although some people will make a good recovery, it can cause persistent problems and can be fatal.

For example, encephalitis due to the herpes simplex virus (the most common type of encephalitis) is fatal in one in five cases even if treated, and causes persistent problems in around half the people who have it.

The chances of successful treatment are much better if encephalitis is diagnosed and treated quickly.

Common complications

Encephalitis can damage the brain and cause long-term problems including:

These problems can have a significant impact on the life of the affected person, as well as their family, friends and carers.

Support and rehabilitation

Recovering from encephalitis can be a long, slow and difficult process. Many people will never make a full recovery.

Specialised services are available to aid recovery and help the person adapt to any persistent problems – this is known as rehabilitation.

This may involve support from:

  • a neuropsychologist – a specialist in brain injuries and rehabilitation
  • an occupational therapist – who can identify problem areas in the person's everyday life and work out practical solutions
  • physiotherapist – who can help with movement problems
  • a speech and language therapist – who can help with communication

Before leaving hospital, the health and care needs of the affected person will be assessed and an individual care plan drawn up to meet those needs.

This should involve a discussion with the affected person and anyone likely to be involved in their care, such as close family members.

See the carers topic for useful information and advice about caring for someone, including information that may be useful if you're new to caring.

Help and advice

The Encephalitis Society is the main support group in the UK.

It can provide information and recommend the right professionals to help you in your situation.

Its helpline number is 01653 699 599. 

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website nhs.uk
Last Updated: 20/10/2022 13:57:45