What exactly is Encephalitis?

Encephalitis means inflammation of the brain. The inflammation is caused either by an infection invading the brain (viral/infectious Encephalitis); or through the immune system attacking the brain in error (Autoimmune Encephalitis).

Who can get Encephalitis?

Anyone at any age can get Encephalitis. There are up to 6000 new cases of Encephalitis each year in England alone.



What causes Infectious Encephalitis?

Viruses are the commonest agents that cause Infectious Encephalitis. Within the British Isles herpes simplex virus (the cold sore virus) is the virus most frequently identified. Worldwide other viruses are responsible, many of which are transmitted by mosquito. In more than half the cases of presumed Viral Encephalitis, the identity of the infecting virus is not conclusively determined. More rarely bacteria, fungus and parasites can cause Encephalitis.



What causes Post-infectious Encephalitis / Autoimmune Encephalitis?

Autoimmune Encephalitis can be triggered by  an infection in which case the term “Post-infectious Encephalitis” is used. ADEM( Acute Disseminated Encephalomyelitis ) is a Post-infectious Encephalitis. The illness usually follows after  a mild viral infection (such as those that cause rashes in childhood) or immunisations. Typically there is a delay of days to two to three weeks between the triggering infection and development of the Encephalitis.


Recently it has been recognised that there are other types of Autoimmune Encephalitis resulting from an attack of the brain by the body’s own immune system. Some of these types of autoimmune Encephalitis are identified by finding a specific antibody in blood. These conditions include Potassium channel complex antibody associated encephalitis, NMDAR and Hashimoto’s Encephalitis



What causes Chronic: Subacute Sclerosing Pan-Encephalitis (SSPE)?

A chronic encephalitis as a result of measles – SSPE is a very rare type of encephalitis which can follow natural (wild) measles virus infection.



What are the main symptoms?

Encephalitis from infectious causes frequently begins with a ‘flu-like illness or headache. Typically more serious symptoms follow hours to days later. The most serious finding is an alteration in the level of consciousness. This can range from mild confusion or drowsiness, to loss of consciousness and coma. Other symptoms include a high temperature, seizures (fits), aversion to bright lights, inability to speak or control movement, sensory changes, neck stiffness, or uncharacteristic behaviour. The types of symptoms seen in Encephalitis reflect the specific areas of the brain affected by inflammation. The range of possible symptoms and their rate of development vary widely; therefore making the diagnosis of Encephalitis can be difficult.


In autoimmune encephalitides presentation can often present as mimicking psychiatric disorders.  There is often a longer onset than that seen in encephalitis of infectious causes.  Symptoms may vary depending on the cause but may include confusion, altered personality or behaviour, psychosis, movement disorders and tic’ing, seizures, hallucinations, memory loss, and sleep disturbances.



How is Encephalitis diagnosed?

Diagnosis of Encephalitis is made where there is evidence of an inflammatory process of the brain in association with clinical evidence of neurologic dysfunction. The range of possible symptoms and their rate of development vary widely, and are not just found in Encephalitis, so making the diagnosis can be difficult.



What tests are undertaken?

• Lumbar puncture – to detect inflammation, as well as the possible presence of bacteria or viruses, in the spinal fluid.
• Brain scans (CT or MRI) – to exclude brain tumours, aneurysms and strokes and show the extent of any inflammation.
• Blood tests – to exclude metabolic encephalopathies.
It is not unusual for the results of tests to be “normal”, it is important to initially exclude some more common and treatable diseases.
• EEG – An electroencephalogram is a recording of brain activity



How is Encephalitis treated?

Treatment of patients with Encephalitis has two aims. First aim is to ensure that the patient receives specific treatment for the cause of their Encephalitis. Where the Encephalitis is thought to be caused either by a virus or bacteria, patients are treated with anti-viral and antibiotic drugs. It is important that these drugs are started promptly, often before a definite cause is found. Therefore patients are frequently given several different drugs at once. Acyclovir is the most frequently used anti-viral drug. It is effective against herpes simplex virus; it is given at high dose into a vein. Unfortunately for many viral infections there are no specific treatments at present.
The second aim is to treat the complications arising from the Encephalitis and to support the patient whilst they are not able to perform their usual bodily functions. Often treatment with anti-convulsants to control seizures, or sedatives to reduce agitation is required. Sometimes patients require Intensive Care treatment including ventilation (mechanical help with breathing).
Because Autoimmune Encephalitis is due to the immune system acting inappropriately treatments aim to modify immune system function. These includes drugs, such as steroids; intravenous immunoglobulin (IVIG) – antibody collected from blood donors; or plasma exchange.



Do people get better?

Nerve cells may be damaged or destroyed by the viral infection, the immune reaction and by pressure resulting from the inflammation. This damage is termed “Acquired Brain Injury” (ABI). Some loss of brain function is therefore a probable outcome of Encephalitis. In some cases, however, this loss occurs on a relatively small scale resulting in very minor impairment, such as some loss in speed of thinking. In other cases damage can be extensive leading to significant impairments.

Recovery may be a long and slow process. An initial period of convalescence with plenty of rest is recommended. This should be followed by a programme of graded activity and rest over 3 – 12 months giving the brain the opportunity to restore function. In more severe cases a period in a brain injury rehabilitation unit may be necessary.



What are the after effects?

There will be a wide variation in how Encephalitis affects the person in the long term. Tiredness, recurring headaches, difficulties with memory, concentration and balance, mood swings, aggression, clumsiness and levels of social perception and understanding are often reported. Epilepsy, as well as being a feature of the acute illness, may develop weeks or months after the illness has subsided. Physical problems may include weakness down one side of the body, loss of sensations and of control of bodily functions and movement. Speech and language problems may also be common features. Speed of thought and reaction are often also reduced.

Significant changes may occur in personality and in the ability to function day-to-day even if there is a complete physical recovery. Coming to terms with these problems can be very distressing and challenging for everyone concerned.




Compared to other infectious diseases, Encephalitis has a high mortality rate. The illness can be very quickly fatal causing extreme trauma for all the family. It is difficult to understand why a virus infection in the modern world can have such devastating consequences.