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What is encephalitis?

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Encephalitis is an uncommon but serious condition that causes inflammation of the brain.

Encephalitis usually begins with flu-like symptoms, such as a high temperature, a headache and joint pain.

More serious symptoms may then develop over the next few hours or days, including:

  • changes in mental state, such as confusion, drowsiness or disorientation
  • seizures (fits)
  • changes in personality and behaviour

Flu-like symptoms that rapidly get worse and affect mental state should be treated as a medical emergency. In these circumstances, immediately request an ambulance.

Read more about the

symptoms of encephalitis

Why does encephalitis happen?

There are several different types of encephalitis that have different causes. The most common are:

  • infectious – inflammation occurs as a direct result of an infection, which is often viral
  • post-infectious – inflammation is caused by the immune system reacting to a previous infection, and can occur days, weeks or sometimes months after the initial infection
  • autoimmune – inflammation is caused by the immune system reacting to a non-infectious cause, such as a tumour
  • chronic – inflammation develops slowly over many months, and can be the result of a condition such as
    , though in some cases there is no obvious cause

There are also several types of encephalitis spread by mosquitoes – such as

Japanese encephalitis
– and ticks, such as
tick-borne encephalitis
. Encephalitis can also be caused by

Read more about the

causes of encephalitis

How is encephalitis treated?

Encephalitis needs urgent treatment, usually in a hospital intensive care unit (ICU). The earlier it's diagnosed, the more successful treatment is.

Treatment depends on the type of encephalitis you have, but may include:

  • anti-viral medication
  • steroid injections
  • immunosuppressants (medicines that stop the immune system from attacking healthy tissue)

Read more about

diagnosing encephalitis
treating encephalitis


Some people make a full recovery from encephalitis. But for many, encephalitis can lead to permanent brain damage and complications, including:

  • memory loss
  • epilepsy
    , a condition that causes repeated seizures
  • personality and behavioural changes
  • problems with attention, concentration, planning and problem solving
  • fatigue (extreme tiredness)

Overall, about 10% of encephalitis cases are fatal.

Read more about the

complications of encephalitis

Preventing encephalitis

It is not always possible to prevent encephalitis. This is because it can be a rare complication of a relatively common infection.

The most effective way to reduce your risk of encephalitis is to make sure you receive the MMR vaccine (for measles, mumps and rubella).

Practicing good hygiene, for example regularly washing your hands with warm water and soap, can help reduce your risk of getting common infections.

Other vaccinations

Vaccinations are also available for Japanese encephalitis, tick-borne encephalitis and encephalitis caused by rabies.

The animals that cause these types of encephalitis are widespread in certain parts of the world. Generally, rabies is more common in Africa, Japanese encephalitis is more common in Asia, and the risk areas for tick-borne encephalitis are the forests of central, eastern and northern Europe.

It is a good idea to discuss these vaccinations with your doctor before travelling.

Read more about the

Japanese encephalitis vaccination
preventing tick-borne encephalitis
and the
rabies vaccination

Encephalitis symptoms

The symptoms of encephalitis are initially mild, but they can quickly become more serious.

Encephalitis usually begins with flu-like symptoms such as:

  • high temperature (fever) of 38ºC (100.4ºF) or above
  • headache
  • nausea and vomiting
  • joint pain

After this initial stage, more serious symptoms can begin to develop within hours or days, which may include:

  • changes in mental state, such as confusion, drowsiness or disorientation
  • seizures (fits)
  • changes in personality and behaviour
  • loss of consciousness

Other symptoms can include:

  • sensitivity to bright lights (photophobia)
  • inability to speak
  • inability to control physical movements
  • stiff neck
  • hallucinations
    (seeing and hearing things that are not actually there)
  • loss of sensation in certain parts of the body
  • partial or total vision loss
  • involuntary eye movements, such as moving the eyes from side to side

When to seek medical advice

Flu-like symptoms that rapidly get worse and affect a person's mental state should be treated as a medical emergency.

In such circumstances, you should immediately request an ambulance.

Encephalitis causes

Encephalitis is usually the result of an infection. In many cases this is caused by a virus, but often no cause is found.

The most commonly identified causes of encephalitis are:

  • the herpes simplex virus, the virus that causes
    cold sores
    and the sexually transmitted infection (STI)
    genital herpes
  • the varicella zoster virus, responsible for
    in children and
    in adults

In rare cases, a bacterial or fungal infection is the cause of encephalitis.

However, no cause can be identified in more than half of all cases. This is thought to be due to the difficulties in diagnosing some types of infection in certain people, rather than the absence of an infection.

How the infection enters the brain

There are thought to be two main ways an infection can spread to the brain – the bloodstream and the nerves.

Usually, the brain is protected from infections by a thick membrane barrier. In most cases this barrier prevents foreign substances from entering the brain, which is why encephalitis or other types of nervous system infections, such as

, are so rare.

However, in a small number of people the infection can pass through the barrier and infect the brain tissue, affecting normal brain function. Further brain damage can occur as the brain swells and presses against the hard inside surface of the skull.

If left untreated, encephalitis can result in a coma and can be fatal.

Animal-related infectious encephalitis

It is possible to develop some types of encephalitis by coming into contact with infected animals. Three of the more common types are briefly described below.

Tick-borne encephalitis (TBE)

Tick-borne encephalitis (TBE) is a viral infection spread by tiny blood-sucking parasites called ticks. TBE can be found in many European countries. Read more about

tick-borne encephalitis

In rare cases, an infection called Lyme disease can cause encephalitis. Read more about

Lyme disease

Japanese encephalitis (JEV)

Japanese encephalitis is a viral infection spread by mosquitoes. It occurs throughout southeast Asia, the Far East and the Pacific islands. People involved in farming in these parts of the world are most at risk. Read more about

Japanese encephalitis


Rabies is a very serious type of encephalitis usually spread when a person is bitten or scratched by an infected animal.

All native UK animals are thought to be free of rabies, with the exception of a single species of bat. Most cases of rabies occur in Africa and Asia, with half of all cases occurring in India. Read more about rabies.

Problems with the immune system

In cases of autoimmune encephalitis and post-infectious encephalitis, the condition is caused by a problem with the immune system (the body's natural defence against infection).

This occurs when the immune system attacks healthy tissue in the brain that it mistakes for a threat, which then causes the brain to become inflamed and swell.

It is often not clear exactly why the immune system malfunctions in this way. Some cases of autoimmune encephalitis are caused by the immune system reacting to the presence of a tumour (an abnormal growth) inside the body.

Post-infectious encephalitis may be a rare complication of some common infections, such as:

  • measles
  • mumps
  • influenza (flu)
  • varicella zoster virus
  • rubella
  • Epstein-Barr virus, which is the virus responsible for glandular fever
  • cytomegalovirus (CMV), a very common infection that usually causes no or very few symptoms
  • HIV

In rare cases, post-infectious encephalitis has developed following vaccination. However, it should be stressed that the risk of developing post-infectious encephalitis as a result of being vaccinated is far outweighed by the risk of developing a condition by not being vaccinated.

Chronic encephalitis

There are several types of chronic encephalitis, including:

  • subacute sclerosing panencephalitis – the inflammation occurs as a complication of a measles infection
  • progressive multifocal leukodystrophy (PML) – this is caused by a usually harmless virus known as the JC virus
  • chronic progressive HIV encephalitis – the infection is caused by HIV itself

Subacute sclerosing panencephalitis is extremely rare. This is partly due to the fall in measles cases as a result of the MMR vaccine.

PML is also quite rare. It mainly only affects people with a severely weakened immune system due to factors such as having an end-stage HIV infection (AIDS).

How is encephalitis diagnosed?

It can be difficult to diagnose encephalitis. This is because the symptoms are similar to other conditions, such as meningitis.

Tests are needed to differentiate encephalitis from other brain conditions so treatment can be started as soon as possible.

Brain scans

CT scans
MRI scans
can be used to highlight the extent of brain inflammation and help to distinguish encephalitis from other conditions, such as
brain tumours
(a swelling in the wall of an artery).

Lumbar puncture


lumbar puncture
, also known as a spinal tap, is used to test a sample of spinal cord fluid. The fluid, called cerebrospinal fluid (CSF), surrounds your brain and spinal cord and supports and protects them.

A hollow needle is inserted into the lower part of your spinal canal so that a sample of CSF can be drawn out for testing. During a lumbar puncture,

local anaesthetic
will be used so that you don't feel pain.

Electroencephalogram (EEG)


electroencephalogram (EEG)
is used to monitor your brain activity. During an EEG, small electrodes are placed on your scalp. These pick up the electrical signals from your brain and display them on a screen or piece of paper.

If you have encephalitis, an EEG may show abnormal brain activity.

Other tests

Screening blood, urine and other body fluids may also help confirm or rule out a diagnosis of encephalitis.

Screening can detect and identify infections of the brain or spinal cord. Results from these tests can also help to exclude conditions similar to encephalitis.

Encephalitis treatment

Encephalitis needs urgent treatment and most cases will be admitted to a hospital intensive care unit (ICU).

Treatment depends on the type of encephalitis you have, but aims to:

  • stop and reverse the process of infection
  • control immediate complications caused by fever, such as seizures or dehydration
  • prevent long-term complications developing

An oxygen mask will be used to help with breathing. Feeding tubes will provide nutrition and help keep the body hydrated.

Encephalitis is a very serious condition and recovery can take months. There is also a significant risk of developing

complications of encephalitis
, such as memory loss, behavioural changes or even death.

Infectious encephalitis

A medicine called aciclovir (sometimes spelt acyclovir) is the used treatment for infectious encephalitis. However, it is only effective in treating cases caused by the herpes simplex virus or varicella zoster virus.

The earlier aciclovir is used, the more successful it is. Therefore, treatment with aciclovir is usually started while the condition is being diagnosed. If tests reveal encephalitis is being caused by something else, alternative treatments will be considered.

Aciclovir works by directly attacking the DNA inside viral cells, which stops the virus from reproducing and spreading further into the brain. It is given directly via a tube into a vein (intravenously), usually three times a day for two to three weeks.

Common side effects of aciclovir include:

  • headache
  • nausea (feeling sick)
  • vomiting
  • diarrhoea

Less common side effects include:

  • liver damage
  • hallucinations (seeing things that are not real)
  • a decrease in the number of white blood cells that are produced by the bone marrow, which can make you more vulnerable to infection

In rare cases where a bacterial or fungal infection causes encephalitis, treatment usually consists of

antifungal medicines

Post-infectious encephalitis

Post-infectious encephalitis is usually treated with injections of high-dose

. This may last several days, depending on the severity of the condition.

Corticosteroids work by calming the immune system (the body's natural defence against infection and illness). This reduces the levels of inflammation inside the brain.

Some people's symptoms may improve a few hours after treatment. But in most cases it will take a few days before symptoms start to improve.

Side effects of corticosteroids include:

  • nausea and vomiting
  • indigestion
  • skin irritation at the site of the injection
  • rapid mood changes, such as feeling very happy one moment and very depressed the next

If your symptoms fail to respond to treatment with corticosteroids, an additional medication called immunoglobulin therapy may be used. This comes from a blood donation and contains specific antibodies that help to regulate the immune system.

If your symptoms do not improve, a therapy called plasmapheresis may be considered. Plasmapheresis involves gradually passing your blood through a machine to remove the parts that contain antibodies before it is returned to your body.

Autoimmune encephalitis

Autoimmune encephalitis can be treated with corticosteroids, immunoglobulin therapy and plasmapharesis. An additional medication known as an immunosuppressant may also be recommended.

Immunosuppressants suppress your immune system, which should prevent your immune system from attacking healthy tissue.

Ciclosporin is a widely used immunosuppressant in the treatment of autoimmune encephalitis.

Common side effects of ciclosporin include:

  • numbness or tingling
  • loss of appetite
  • nausea and vomiting
  • high blood pressure
  • tremor
    (uncontrollable shaking or trembling)
  • muscle pains or cramps
  • increased body hair growth

Chronic encephalitis

There is currently no cure for the subacute sclerosing panencephalitis (SSPE) type of chronic encephalitis. Anti-viral medication can slow its progression, but this condition inevitably proves fatal within one to two years of receiving a diagnosis.

The recommended treatment for progressive multifocal leukoencephalopathy (PML) type of chronic encephalitis usually depends on what is causing the immune system to weaken.

If the immune system is weakened due to a treatment such as

or taking immunosuppressants, this treatment may be temporarily withdrawn.

If your immune system is weakened due to a HIV infection, a type of medication known as highly active antiretroviral therapy may be effective. For more information, see

treating HIV

HIV medication can also effectively treat chronic progressive HIV encephalitis if used early. If it is left untreated, it is fatal.

Complications of encephalitis

Although some people will make a good recovery after having encephalitis, the condition can cause significant complications and can be fatal.

The chances of successful treatment are much better if the condition is diagnosed and treated quickly.

However, even with treatment it can be fatal. About 20% of people treated for encephalitis caused by the herpes simplex virus – one of the most common but serious forms of the condition – will die.

Overall, about 10% of encephalitis cases are fatal. In some cases, people survive with one or more long-term complications due to damage to the brain.

The most common complications include:

  • memory problems, which affect 70% of people with complications
  • personality and behavioural changes, which occur in just under half of all people
  • aphasia
    – speech and language problems that occur in around one in three people
  • epilepsy
    , which occurs in one in four affected adults and one in two affected children
  • changes in emotions, such as anxiety and anger, and mood swings
  • problems with attention, concentrating, planning and problem solving
  • physical and motor difficulties
  • low mood and a sense of feeling different
  • fatigue (extreme tiredness)

Individual care plans

Due to these complications, specialised services are often needed during recovery, including from:

  • a neuropsychologist – a specialist in brain injury and cognitive rehabilitation
  • an
    occupational therapist
    – they can identify problem areas in a person's everyday life and help work out practical solutions
  • a
    – a therapist who uses physical methods, such as massage, manipulation and exercise
  • a speech and language therapist – they use specialist techniques to improve all aspects of communication

Before being discharged from hospital, your health and social care needs will be fully assessed and an individual care plan drawn up to meet those needs.

If you are the primary carer of someone recovering from encephalitis, such as their spouse or parent, you should be invited to take part in discussions about the care plan, and your own circumstances and requirements should be taken into account. You should also be given information about support services available in your local community.

Caring for someone with emotional and behavioural problems can be stressful, so it is important you do not neglect your own mental and physical wellbeing. See Carer wellbeing for more information and advice.

Seeking further help

Seek additional help if you are experiencing problems after having encephalitis. Many healthcare professionals are unaware of the problems following encephalitis, and it can sometimes be a struggle to find the right help for you.

The Encephalitis Society can provide you with appropriate sources of information and recommend the right professionals to help you in your situation.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.