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:

• MMR (measles, mumps and rubella) vaccine – a routine vaccination offered to all children in Wales
• 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 areas where access to medical care is likely to be limited

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.

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.

The condition 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 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".

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.