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 do not always appear and sometimes the first signs of encephalitis may be more serious symptoms.

Serious symptoms

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

• confusion or disorientation
• drowsiness
• seizures or 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 are not 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 does not 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.

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).

Infections

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.

Encephalitis is most often due to a virus, such as:

• herpes simplex viruses, which cause cold sores and genital herpes (this is the most common cause of encephalitis)
• the varicella zoster virus, which causes chickenpox and shingles
• measles, mumps and rubella viruses
• viruses spread by animals, such as tick-borne encephalitis, Japanese encephalitis, rabies (and possibly Zika virus)

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 is not 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 happens 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 vaccination far outweigh the risk of encephalitis)

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 2 main types of scan used are:

• a CT scan 
• an MRI scan

Lumbar puncture

A 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 may include:

• an electroencephalogram (EEG) – where 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.

Treating the cause

If a cause of encephalitis is found, treatment will start straight away.

Possible treatments include:

• antiviral medicine – used if encephalitis is caused by the herpes simplex or chickenpox viruses; it's usually given into a vein three times a day for 2 to 3 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 – medicine that helps control the immune system
• plasmapheresis – a procedure which removes the substances that are attacking the brain from the blood
• surgery to remove abnormal growths (tumours) – if encephalitis was triggered by a tumour somewhere in the body
• antibiotics or antifungal medicine – used if encephalitis is caused by a bacterial or fungal 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.

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 high temperature
• medicine to control seizures or fits
• medicine 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
• medicine 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 medicine is not 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 1 in 5 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:

• memory problems 
• personality and behavioural changes 
• speech and language problems
• swallowing problems
• repeated seizures or fits – known as epilepsy
• emotional and psychological problems, such as anxiety, depression and mood swings
• problems with attention, concentrating, planning and problem solving
• problems with balance, co-ordination and movement
• persistent tiredness

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
• a 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 our social care and support guide 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.