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, but these don’t always occur.

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.

Read more about the symptoms of encephalitis and how encephalitis is diagnosed.

Causes of encephalitis

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

  • viral infections – several common viruses can spread to the brain and cause encephalitis in rare cases, including the herpes simplex virus (which causes cold sores and genital herpes) and the chickenpox virus
  • 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.

Read more about the causes of encephalitis.

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 (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.

Read more about how encephalitis is treated.

Recovering from encephalitis

Some people will eventually make a full recovery from encephalitis, although this can be a long and frustrating process.

But 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.

Read more about the complications of encephalitis.

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.