Encephalitis is a serious brain condition usually caused by a virus. If you think or your child may have encephalitis, seek medical attention straight away.
Causes of encephalitis
Encephalitis is an inflammation of the brain. It is rare but it is potentially life-threatening and can lead to permanent brain damage.
It has many different causes, including:
- the herpes simplex virus (which also causes cold sores)
- enteroviruses, which enter through the mouth and are absorbed through the gut
- viruses transmitted by mosquito bites (including Murray Valley encephalitis, Japanese encephalitis, Zika virus and equine encephalitis)
- having a 'childhood disease' such as chicken pox, measles, mumps or rubella (German measles)
- a bacterial infection
- an autoimmune disease
There are two types of encephalitis:
Primary encephalitis: when the virus or bacteria infects the brain.
Secondary encephalitis: when the immune system reacts to an infection elsewhere in the body and starts attacking brain cells. Secondary encephalitis normally happens 2 to 3 weeks after the initial infection.
Symptoms tend to come on very suddenly and may include:
- a high fever
- stiff neck
- sensitivity to light
- in babies, a bulging fontanelle
Many of these symptoms also happen in other illnesses, like migraines. Having a fever is an important way of distinguishing encephalitis.
In very severe cases, encephalitis can lead to coma and even death. In less severe cases, people who have had encephalitis might experience fatigue, weakness, lack of coordination and problems with their vision, memory, hearing and speech for several months. Sometimes these problems are permanent.
Most people with encephalitis are admitted to hospital. A number of tests are used to diagnose the cause, including:
- MRI or CT images of the brain to check for swelling or another cause of the symptoms, such as a tumour
- a lumbar puncture to see if there is inflammation of the brain and to identify what virus or bacteria has caused the condition
- blood or urine tests, or a swab taken from the back of the throat, which might identify viruses or bacteria
- electroencephalogram (EEG) to measure the brain’s electrical activity
- brain biopsy (only for patients who are deteriorating or when the cause of the encephalitis isn’t clear)
The treatment will depend on the cause of the encephalitis.
People who have a severe infection may need help with breathing. In mild cases, treatment usually involves bed rest, plenty of fluids and anti-inflammatory medicine.
Afterwards, people sometimes need help with speech therapy, occupational therapy or physiotherapy to manage longer lasting symptoms.
When to seek help
If you or the person in question, adult or child, has an unexplained fever, is generally unwell and suddenly seems to be very drowsy and confused, especially if they’ve recently had a viral illness such as chickenpox or measles, seek medical attention straight away.
For more information and the latest research on encephalitis, visit the Brain Foundation website.
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Last reviewed: May 2020