Encephalitis is inflammation of the brain. It is usually caused by a viral infection. Examples of viral infections that can cause encephalitis include herpes simplex virus (the virus that causes cold sores and genital herpes), varicella zoster virus (the chickenpox virus), mumps virus, measles virus and flu viruses.

Most cases of encephalitis are caused by the virus directly infecting the brain. However, sometimes encephalitis can develop if your immune system tries to fight off a virus and, at the same time, attacks the nerves in your brain in error. This is known as post-infectious or autoimmune encephalitis.

What is the difference between encephalitis and meningitis?

Meningitis is an inflammation of the lining that covers the brain and spinal cord (the meninges). It is usually caused by a bacterial or viral infection. Sometimes you can have both encephalitis and meningitis at the same time. This is called meningoencephalitis.

You are also more likely to develop encephalitis if your immune system is compromised in some way.

What are the symptoms of encephalitis?

The symptoms usually start with the common symptoms of a viral infection: fever, headache, muscle aches, feeling tired and nausea and vomiting. As the infection starts to attack the brain, your behaviour becomes odd. You can become confused and drowsy and can develop a severe headache. You may develop a stiff neck and back and photophobia (an intolerance of light). Muscle weakness or paralysis can occur. Eventually you can become unconscious. Babies with encephalitis can be off their feeds and appear irritable and/or drowsy. They may also develop seizures.

How is encephalitis diagnosed?

Encephalitis can be difficult to diagnose. This is because other things such as meningitis, stroke and sometimes brain tumours can cause similar symptoms. Therefore, you may have various tests before encephalitis can be diagnosed.

Computerised tomography or magnetic resonance imaging scan.

Lumbar puncture

A lumbar puncture  is a procedure where a sample of cerebrospinal fluid (CSF) is taken for testing. CSF is the fluid that surrounds the brain (cerebrum) and spinal cord. A lumbar puncture can look for signs of the virus and can also help to exclude meningitis.


The electroencephalograph (EEG) test looks at your brainwaves and can show abnormal brainwaves that occur if you have encephalitis.

Other tests

These can include blood tests, urine tests, swab tests.

What is the treatment for encephalitis?

Someone with suspected encephalitis needs to be admitted to hospital urgently. Antiviral medication is usually prescribed if encephalitis is suspected. The most common medicine that is used is aciclovir. Antibiotics may also be given initially. This is because, without test results, it may be difficult to tell the difference between encephalitis and meningitis caused by bacteria. Other treatments to help your body to rest and try to fight the infection include intravenous fluids, medicines to control any seizures that you may have, medicines to help with high fever and pain and oxygen given via a face mask.

What is the prognosis (outlook) for encephalitis?

Some people recover from encephalitis and have few, or no, long-term problems. However, in many people, encephalitis is a serious condition and can be life-threatening. Also, after encephalitis, it is common for people to be left with some permanent brain damage. The extent and severity of brain damage can vary greatly.

  1. Problems with balance, co-ordination and dexterity.
  2. Speech problems.
  3. Weakness and problems with movement.
  4. Swallowing problems.
  5. Seizures (fits).
  6. Chronic headache.
  7. Personality changes.
  8. Memory problems.
  9. Behavioural problems.
  10. Mood problems, anxiety and depression.
  11. Difficulty concentrating.

Immunisation is also available against viruses that can cause encephalitis in other countries, such as Japanese B encephalitis and tick-borne encephalitis caused by insect bites. Insect repellant sprays and wearing protective clothing, such as long sleeves, can also be helpful in preventing infection.

Herpes simplex infection in newborn babies is an uncommon complication of active genital herpes in the mother around the time of delivery. It can also (very rarely) occur after direct contact with a herpes blister (such as a cold sore) in someone who is looking after the baby

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