Encephalitis is a rare but serious condition that causes inflammation of the brain. 

It usually begins with flu-like symptoms, such as a high temperature,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. Dial 999 immediately to request an ambulance.

What causes encephalitis?

There are several different types of encephalitis and each type has a different cause. The most common types of encephalitis 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 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 due to a condition such as HIV; in some cases, there's 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 rabies.

In the UK, all types of encephalitis are relatively rare. The Encephalitis Society estimates that there are 4,000 case of encephalitis in the UK each year.

Anyone can be affected by encephalitis, but the very young and the very old are most at risk, because their immune systems tend to be weaker.

Treating encephalitis

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 attacking healthy tissue)


Some people make a full recovery after having encephalitis. However, for many it can lead to permanent brain damage and complications, including:

memory loss


personality and behavioural changes

problems with attention, concentration, planning and problem solving  

fatigue (extreme tiredness)

Overall, about 10% of encephalitis cases are fatal.

Preventing encephalitis

It's 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 getting encephalitis is to ensure you have the MMR vaccine (for measles, mumps and rubella).

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

Other vaccinations

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

These types of encephalitis are rare in the UK, but more widespread in certain parts of the world. For example, rabies tends to be 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.

You should discuss these specific vaccinations with your GP before travelling.

Symptoms of encephalitis 

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 38C (100.4F) or above


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

Flu-like symptoms that rapidly get worse and affect a person's mental state should be treated as a medical emergency. Dial 999 immediately to request an ambulance.

Other symptoms of encephalitis can include:

sensitivity to bright lights (photophobia)

inability to speak

inability to control physical movements

stiff neck

hallucinations (seeing and hearing things that aren't there)

loss of sensation in certain parts of the body

partial or total vision loss

involuntary eye movements, such as side-to-side eye movement

Causes of encephalitis 

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

In the UK, the most common viruses linked to encephalitis are:

In rare cases, encephalitis is caused by a bacterial or fungal infection.

However, no cause can be identified in over 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.

The brain is usually protected from infections by a thick membrane. In most cases, the membrane acts as a barrier by preventing foreign substances entering the brain. This is why encephalitis or other types of nervous system infections, such as meningitis, are so rare.

In a small number of people, an infection can pass through the barrier and into the brain tissue, affecting normal brain function. Further brain damage can occur as the brain swells and presses against the inside of the skull.

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

Animal-related infectious encephalitis

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

Tick-borne encephalitis

Tick-borne encephalitis (TBE) is a viral infection spread by tiny blood-sucking parasites called ticks. TBE is rare in the UK, but can be found in many other European countries.

In rare cases, an infection called Lyme disease, which is spread by ticks in the UK, can cause encephalitis.

Japanese encephalitis

Japanese encephalitis (JEV) is a viral infection spread by mosquitoes. It occurs throughout southeast Asia, the Far East and the Pacific islands. People in these parts of the world who work on farms are most at risk.


Rabies is a very serious type of encephalitis you can get if you're bitten or scratched by an infected animal.

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

Immune system problems

Autoimmune encephalitis and post-infectious encephalitis are caused by a problem with the immune system (the body's natural defence against infection).

The immune system mistakes healthy tissue in the brain as a threat and attacks it, causing the brain to become inflamed and swell. It's not always clear 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 can be a rare complication of some common infections, such as:

In rare cases, post-infectious encephalitis has occurred following vaccination. However, it's important to stress 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 is extremely rare. This is partly due to the decrease 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).

the herpes simplex viruses, which cause cold sores and genital herpes

the varicella zoster virus, which is responsible for chickenpoxand shingles



influenza (flu)

varicella zoster virus


Epstein-Barr virus, which causes glandular fever

cytomegalovirus – a common infection that usually causes few or no symptoms


subacute sclerosing panencephalitis – the inflammation occurs as a complication of a measles infection

progressive multifocal leukodystrophy (PML) – caused by a usually harmless virus known as the JC virus

chronic progressive HIV encephalitis – caused by HIV itself

Diagnosing encephalitis 

Diagnosing encephalitis can be difficult because the symptoms are similar to those of other conditions, such as meningitis.

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

In the UK, encephalitis is a notifiable disease, which means that if a doctor diagnoses the condition they must notify their local authority.

Brain scans

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

Lumbar puncture

A 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, supporting and protecting 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. Local anaestheticwill be used so that you don't feel any pain.

Electroencephalogram (EEG)

An electroencephalogram (EEG) is used to monitor your brain activity. Small electrodes are placed on your scalp, which 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 bodily fluids may also help to confirm or rule out encephalitis.

Screening can detect and identify brain or spinal cord infections. Results from these tests can also be used to help exclude conditions that are similar to encephalitis. 

Treating encephalitis 

Encephalitis needs to be treated urgently and most people with the condition will be admitted to a hospital intensive care unit (ICU).

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

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's also a significant risk of developing complications of encephalitis, such as memory loss, behavioural changes or even death.

Infectious encephalitis

In the UK, a medicine called aciclovir (sometimes spelt acyclovir) is the most widely used treatment for infectious encephalitis. However, it's 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, so treatment is usually started while the condition is being diagnosed. If tests reveal encephalitis is being caused by something else, the treatment will be changed.

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

Aciclovir causes some side effects, include vomiting and diarrhoea. Less commonly, it can lead to liver damage, hallucinations and a decrease in the number of white blood cells 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 antibiotics or antifungal medicines.

Post-infectious encephalitis

Post-infectious encephalitis is usually treated with injections of high-dose corticosteroids. 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. However, in most cases, it will take a few days before symptoms start to improve.

Side effects of corticosteroids include:

If your symptoms don't 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 still don't 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's 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 it attacking healthy tissue. Ciclosporin is an immunosuppressant that's widely used to treat autoimmune encephalitis.

Common side effects of ciclosporin include:

Chronic encephalitis

There's 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 two years of being diagnosed.

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

If the immune system is weakened due to a treatment such aschemotherapy, this treatment may be temporarily withdrawn.

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

If used early, HIV medication can also be an effective treatment for chronic progressive HIV encephalitis. If left untreated, it's fatal.

stop and reverse the process of infection

control immediate complications caused by fever, such as seizures or dehydration

prevent long-term complications developing

nausea and vomiting


skin irritation at the site of the injection

rapid mood changes, such as feeling happy one moment and depressed the next

numbness or tingling

high blood pressure (hypertension)

tremor (uncontrollable shaking or trembling)

muscle pains or cramps

increased body hair growth

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, encephalitis can be fatal. About 1 in 5 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 1 in 10 encephalitis cases are fatal. In some cases, people survive with one or more long-term complications due to brain damage.
The most common complications of encephalitis include:

Individual care plans

Due to these complications, specialised services are often needed during recovery. For example, a person with encephalitis may need help from:

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're the primary carer of someone recovering from encephalitis, 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.

Our care and support section provides lots of useful information and advice about caring for someone, including information that may be useful if you're new to caring.

Seeking further help

Seek additional help if you're 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. Their helpline number is 01653 699 599. 

memory problems – which affect 7 out of 10 people with complications

personality and behavioural changes – which occur in just under half of all people

aphasia – speech and language problems, which occur in about 1 in 3 people

epilepsy – which occurs in 1 in 4 affected adults and 1 in 2 affected children

changes in emotions – such as anxiety, 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)

a neuropsychologist – a brain injury and cognitive rehabilitation specialist 

an occupational therapist – they can identify problem areas in a person's everyday life and help to work out practical solutions

a physiotherapist – who can help restore movement and function when someone is affected by injury, illness or disability

a speech and language therapist – who use specialist techniques to improve all aspects of communication