What is encephalitis?

Encephalitis is a condition which occurs when the brain tissue becomes inflamed; it is not the same as meningitis, which causes the membranes surrounding the brain to become swollen. Encephalitis is a serious condition and is usually caused by an infection, though it is also associated with autoimmune conditions, which cause the body to produce an abnormal immune response.

The condition of encephalitis is uncommon in the UK, affects both men and women and is most common in very young children and the elderly since their immune systems are weaker. It is estimated that around 4,000 cases of encephalitis are diagnosed in the UK every year. The condition is more common in other areas of the world and there are specific types of encephalitis, including Japanese encephalitis, Australian encephalitis and Colorado tick fever (also known as tick-borne encephalitis).

What causes encephalitis?

Encephalitis is not a straightforward condition and there are many possible causes. In many cases, an infection is the source (usually viral) and in the UK the main causes are exposure to the herpes simplex virus and varicella zoster virus. In almost half of cases, no exact cause can be identified. Infection spreads to the brain via the bloodstream or the nervous system, when the blood-brain barrier, which is responsible for protecting the brain, is broken.

Some types of encephalitis can be caused by contact with animals: these include tick-borne encephalitis, rabies encephalitis and Japanese encephalitis. Tick-borne encephalitis is spread by parasites known as ticks, Japanese encephalitis is spread by mosquitoes and rabies encephalitis is spread by animals infected with rabies.

Encephalitis can also develop after an infection, which is known as post-infectious encephalitis. Conditions that may increase the risk of encephalitis include:

• Measles.
• Chickenpox.
• Rubella.
• Mumps.
• Influenza (flu).
• HIV.
• Glandular fever caused by the Epstein-Barr virus.

Symptoms of encephalitis

Encephalitis is a serious, potentially life-threatening condition, which usually causes flu-like symptoms and then more serious signs. Initially symptoms include:

• Fever (high temperature).
• Nausea and sickness.
• Joint pain.
• Headaches.

More advanced symptoms include:

• Seizures.
• Becoming confused and dizzy.
• Drowsiness.
• Changes in behaviour.
• Increased sensitivity to light.
• A stiff neck.
• Hallucinations.
• Loss of feeling in parts of the body.
• Lack control of bodily movements.

How is encephalitis diagnosed?

You should see a doctor if you have flu-like symptoms that develop quickly and you start to experience changes in your mental state. Encephalitis is a very serious condition so it is important that you seek urgent medial help by calling 999, and the earlier you are diagnosed and treated the better.

If you have symptoms of encephalitis doctors will work as quickly as possible to diagnose the condition. Two tests are usually used to reach a diagnosis, which are a lumbar puncture and brain scans. CT and MRI scans will show the extent of inflammation of the brain tissue, while a lumbar puncture will detect an infection in the cerebrospinal fluid.

Complications of encephalitis

If encephalitis is diagnosed and treated quickly, it is likely that the patient will recover well. However, there is a possibility of long-term complications, including:

• Difficulty remembering.
• Changes in behaviour and personality.
• Speech and language difficulties (known as aphasia).
• Epilepsy.
• Difficulty concentrating.
• Mood swings.
• Feeling low.

Individuals who are recovering from encephalitis are usually cared for by a multi-disciplinary team of healthcare professionals, since they may require different kinds of specialist help.

Treating encephalitis

Treatment for encephalitis is designed to stop the infection progressing, prevent and ease complications (such as fitting) and reduce the risk of long-term complications. The most common treatment used for infectious encephalitis caused by the herpes simplex virus is a type of medication called acyclovir. This treatment is more effective if used early, so it is often prescribed before diagnostic tests are conducted. Aciclovir attacks the DNA inside the infectious cells, which prevents the virus from reproducing. The drug is given intravenously for a period of 2 to 3 weeks. Possible side-effects of aciclovir include:

• Diarrhoea.
• Headaches.
• Nausea.
• Vomiting.

In rare cases, aciclovir can also cause the following side-effects:

• Hallucinations.
• Damage to the liver.
• Decreased white blood cell production: this can increase your risk of developing infections and illnesses.

High doses of corticosteroids are usually used for post-infectious encephalitis and medication is injected on a regular basis for a short period of time. Corticosteroids help to reduce inflammation but long-term doses are not advised because they cause unpleasant side-effects, including:

• Nausea and sickness.
• Indigestion.
• Bigger appetite.
• Irritated skin around the site of the injections.
• Mood swings.

If encephalitis is associated with autoimmune conditions, it can usually be treated with corticosteroids, immunoglobulin therapy and immunosuppressants (medication that suppresses the actions of the immune system and help to reduce inflammation).

Preventing encephalitis

The best way to prevent encephalitis is to have the MMR (measles, mumps and rubella) vaccination; the MMR is available to all children in the UK and is part of the routine vaccination programme. The first vaccination is given to children at the age of 13 months and this is followed by a pres-school booster injection, which is usually given between the ages of 3 and 5 years.

There are also vaccinations available for Japanese and tick-borne encephalitis and you may wish to get the immunisation if you are planning to travel to countries where the condition is common. Ask your GP about travel advice. Also, make sure you leave plenty of time to have injections before you set off, as some need to be given well in advance. The vaccination is generally advised for travel to certain parts of Asia and the South Pacific.