Tue. Apr. 20 2004
Researchers at Toronto's Hospital for Sick Children have found a strong association between infection with Epstein Barr virus and multiple sclerosis, a finding which could help science tease out some of the complex genetic and environmental factors that trigger the disease.
It doesn't mean that Epstein Barr virus causes MS, or that infection with that virus is necessary to develop the debilitating condition.
But it could mean that in at least some -- perhaps many -- children predisposed to developing MS, infection with Epstein Barr could ignite the process, or fuel it if it is already underway.
"It's unlikely that we'll ever be able to halt MS until we understand what the process is that leads to it in more detail than we know today. And I think this study does shed some light on the process -- or a process -- that could lead to MS," said MS researcher Dr. Paul O'Connor, who was not involved in the study.
The work, published Tuesday in the Journal of the American Medical Association, was conducted by scientists at Sick Kids and at Al-Sabah Hospital in Shuwaikh, Kuwait.
Scientists have long thought that MS is not caused by one or more genetic mutations, but is instead likely the result of a genetic predisposition set off by some environmental triggers and perhaps some disorders of the body's immune system.
One prevalent theory has revolved around Epstein Barr, the virus that causes mononucleosis. By adulthood, most people have been infected with the virus, which can remain dormant and cause no illness. Testing adult MS patients for Epstein Barr virus would tell little about whether it is a cause or simply a coincidence.
Children, however, are less likely to be infected by the virus, which is generally acquired in the later teenage years. So Dr. Brenda Banwell, director of Sick Kids' pediatric MS clinic, decided to compare infection rates among children with MS and healthy children to see if a difference was apparent.
"This was the first attempt that anyone has ever done to look for triggers of MS in a pediatric MS population," she said.
"Our population is uniquely able to bring us to the beginnings of the disease."
Infection rates among children with MS were nearly twice as high as among healthy kids, she and her colleagues found. Of 30 children with MS, 83 per cent had antibodies to the virus -- a sure sign they'd been infected. Only 41 per cent of two groups of healthy children had the virus.
"What we found is an association and a fairly powerful one in the sense of how frequently we found it," said Banwell, senior author of the study.
"But the issue is: Are children with MS just more likely to develop Epstein Barr virus? It could be the reverse. It may not be that Epstein Barr virus is a trigger of the immune response, it may be that children with MS are fundamentally more prone to develop early infection."
However, testing for antibodies to other common infections showed the kids with MS weren't getting sick with everything going around. If anything, Banwell said, their immune systems weren't depressed, they were too active.
That testing turned up a surprise for the researchers. They discovered the healthy children were much more likely to have been infected with the herpes virus than the children with MS, leading them to wonder if infection with the herpes simplex virus might actually be protective against multiple sclerosis.
Banwell suggested it may turn out that what viruses a person catches, in what order and at what point in their lives may be a crucial determinant in whether they develop MS.
"It may well be that infection with a virus like Epstein Barr virus at a key time changes fundamentally your immune system -- which we know it does in everyone to a certain point-- but may then activate the immune system against targets that they shouldn't be activated against," said Banwell, a pediatric neurologist.
O'Connor, who heads the multiple sclerosis clinic at Toronto's St. Michael's Hospital, said more work needs to be done to prove the findings. Still, he found the idea of a link between Epstein Barr and MS plausible.
"I don't think Epstein Barr virus is sort of the silver bullet that hits you and causes MS," he said.
"But it could be one of several different factors that leads to immune disregulation which in turn causes MS."
Banwell said her team is now conducting a much larger study looking
at children with MS in five different countries in an effort to confirm
the Epstein Barr and the herpes simplex findings.
Copyright © 2004, Canadian Press