People who get glandular fever in childhood may be more prone to the wasting disease multiple sclerosis.

People who get glandular fever in childhood may be more prone to the wasting disease multiple sclerosis.

Researchers have shown that exposure to the Epstein-Barr virus, which causes glandular fever, is twice as common in children who develop multiple sclerosis under the age of 18.

It has long been suspected that the Epstein-Barr virus might play a role in multiple sclerosis but it has proved almost impossible to investigate because nearly 90 per cent of healthy adults in Western countries have been exposed to the virus at some point in their lives. The disease affects 80,000 people in Britain.

Now Canadian researchers say that it is not the virus itself but the time at which infection occurs that may be the critical factor. Doctors from the Hospital for Sick Children in Toronto, who carried out the new study, suggest there is a window during childhood when infection with the Epstein-Barr virus can trigger multiple sclerosis.

Children are less likely to have been infected with the virus than adults because they have not had time to be exposed to it. About 5 per cent of multiple sclerosis patients develop the disease before they are 18.

Comparing children with multiple sclerosis with healthy controls, the researchers found 83 per cent of the MS patients showed evidence of past infection with the Epstein-Barr virus whereas only 42 per cent of the healthy children did. Brenda Banwell, an assistant professor of paediatrics at the University of Toronto, who led the research published in the Journal of the American Medical Association, said: "We think the Epstein-Barr virus plays an important role in the development of MS, because the genetic code of the virus contains sequences that are identical to genetic sequences in the myelin basic protein, which is expressed in the brain, and destroyed in MS."

The muscle-wasting and the disorders of vision, balance and sensation that characterise multiple sclerosis are caused by progressive destruction of the myelin (protein) coat that surrounds and protects the nerves.

Professor Banwell said: "It is conceivable that the immune system mounts a response to that genetic sequence in the Epstein-Barr virus, then sees it in myelin and targets it as well."

The causes of multiple sclerosis have puzzled doctors for decades but Professor Banwell believes the study of children with the disease may yield new insights. The condition is thought to be caused by the interaction of a genetic predisposition, environmental triggers (such as infections) and an abnormal immune system response.

Professor Banwell said: "We suspect that it is the sequence and timing of viral exposure and how this modifies an individual's immune response that is important. Children with MS are the closest to the biological onset of the disease, which allows us to look at a whole host of causative factors that are very difficult to study in adults."