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Health Protection Agency (HPA) scientists have shown that specific antibodies, which are produced by a patient's own immune system, are a more common cause of encephalitis than previously recognised. This new finding was revealed in a study published in the Lancet Infectious Diseases yesterday.

Encephalitis is a rare, but often deadly, inflammation of the brain, which often starts as a flu like illness or headache with symptoms rapidly getting worse over a short period of time. A person may experience seizures (fits), changes in mental state, such as confusion or drowsiness, a loss of consciousness, or lapse in to a coma.

The most common known causes of encephalitis are infections by a virus. But, in most cases, a cause is never found, which makes it difficult to devise new treatments or develop interventions to prevent serious complications.

Around 700 people in England develop acute encephalitis every year and about 7% of these cases are fatal. In the largest study of its kind in England, led by scientists at the HPA, over 200 patients with encephalitis were studied. Researchers found a cause for 63% of cases, the most frequent being the herpes simplex virus, which usually causes cold sores with no serious complications. But they also found that almost 10% of all cases were caused by antibodies made by the body's immune system against certain brain proteins and not caused directly by infection. Whilst it had previously been known that this could be a cause, the frequency with which it occurred had not previously been established.

The importance of these results is that it shows drugs to "dampen down" the immune system are more likely to be required to treat encephalitis than previously thought, as brain damage is thought to occur through immune attack of the brain.

Dr David Brown, director of the HPA's virus reference department, said: "The aim of this study was to learn more about the many causes of encephalitis and we are delighted that our findings have significantly contributed to our knowledge of the disease.

"We found that almost 10% of all cases in the group of patients we studied were related to antibodies found within the brain. These patients were also shown to have the worst outcomes. But the good news is that this form of encephalitis is potentially treatable, especially when therapy is started early, so it is hoped our findings will help clinicians in diagnosing and treating patients as early as possible."

Dr Brown continued: "This important study has led to the production of a national clinical case definition for encephalitis and also better methods for identifying the cause. It has also pulled together multi-disciplinary experts from around the country with an interest and expertise in encephalitis, creating a unique knowledge network here in the UK, which could also benefit patients worldwide. We have also received lots of interest from colleagues from all around the world."

Notes for editors: 

1. 'Causes of encephalitis and differences in their clinical presentations in England: a multicentre, population-based prospective study' is published in Lancet Infectious Diseases. The HPA authorial team, led by Chief Investigator Natasha Crowcroft, included Julia Granerod and the world leading virologist, David Brown.
2. Extensive laboratory testing was carried out on samples collected from over 200 encephalitis patients for the purposes of the study. Researchers found a cause for 63% of cases, of which herpes simplex virus was the most frequent cause of illness. However, the researchers found that a significant proportion of cases were due to immune-mediated, rather than infectious, forms of the disease.
3. Among the group of encephalitis patients studied, 8% were associated with either the voltage-gated potassium channel or the N-methyl-D-aspartate receptor - both being proteins found within the brain.
4. Further information on encephalitis can be found on the HPA website. See also:
   NHS Choices: http://www.nhs.uk/Conditions/Encephalitis/Pages/Introduction.aspx
   The Encephalitis Society: http://www.encephalitis.info/default.aspx

For further information on this press release please contact the HPA press office on:

Eleanor Bunch             020 8327 7751
Emma Gilgunn-Jones  020 8327 6647
Alexandra Baker         020 8327 7098
Georgina Fletcher       020 8327 6690
Louise Brown              020 8327 7080
Kate Swan                  020 8327 7097