Cold sores and chicken pox could be linked to many cases of potentially fatal encephalitis, a study suggests.
Researchers investigating the causes of the brain condition found a strong association with the virus responsible for cold sores and sexually transmitted herpes.
The herpes simplex virus accounted for 19pc of infection-related encephalitis.
Other infectious triggers were identified as varicella zoster virus -- which causes chicken pox and shingles -- and tuberculosis bacteria.
Encephalitis begins as a flu-like illness and can progress to deadly inflammation of the brain.
Patients who survive may be left paralysed or develop movement disorders, muscle weakness, tremors and confusion.
Early and accurate diagnosis is essential if patients are to receive appropriate treatment. However, the condition has many causes which remain unidentified for up to 85pc of patients worldwide.
An estimated 700 cases of viral encephalitis are diagnosed in England each year.
The new study, reported in 'The Lancet Infectious Diseases' medical journal, involved 203 patients with suspected encephalitis at 24 hospitals across England.
Genetic and antibody testing revealed a cause for 63pc of patients, with infections accounting for 42pc of cases.