Epstein-Barr virus may play a key role in triggering a debilitating neurogical disease multiple sclerosis ~ Canadian research

[Guest guest]

One of the most commonplace microbes, Epstein-Barr

virus, may play a key role in triggering the

debilitating neurological disease multiple sclerosis,

Canadian researchers have discovered.

The link between EBV, the virus that can cause

mononucleosis, and MS has long been suspected but

research conducted at the Toronto Hospital for Sick

Children provides some of the strongest evidence yet

that childhood exposure could be an important factor.

" Our thinking is that it's not whether you get the

virus that's important, but when, " Dr. Banwell,

director of the hospital's pediatric MS clinic, said

in an interview. " We think it may be a timing and

vulnerability issue. "

The research, published in today's edition of the

Journal of the American Medical Association, was

conducted by looking at blood samples from children

with MS, children who came to the emergency room and

healthy children in the community.

About 83 per cent of the children with MS had been

exposed to EBV, compared with 42 per cent of the other

children. Exposure rates to a number of other common

viruses were similar in the two groups, with the

exception of herpes simplex virus (the virus that

causes cold sores).

Children with MS were actually far less likely to have

been exposed to herpes.

This led researchers to think that the order in which

children are exposed to common microbes may also play

a role in their risk of developing MS.

In other words, an immune system that has already

wrestled with herpes may be better prepared to deal

with EBV. Multiple sclerosis is a bedeviling disease

of the brain, spinal cord and optic nerves that can

cause problems with muscle control and strength,

balance, vision and sensation.

More than 50,000 Canadians have MS. In fact, Canada

has one of the highest rates of MS in the world. In

people with MS, for reasons that are unclear, the

body's immune system malfunctions and starts attacking

myelin, the protein coating that surrounds and

protects nerve fibers.

This is an important link because the genetic code of

the Epstein-Barr virus contains sequences that are

identical to genetic sequences in myelin protein.

Dr. Banwell said it is " conceivable that the immune

system mounts a response to that genetic sequence in

EBV, then sees the myelin and targets it as well. "

In other words, the immune system thinks it is

attacking the virus when it is actually attacking

healthy nerve cells. With this information, scientists

could, theoretically, find a way to stimulate the

immune system so that it does not attack myelin

protein and hence prevent some cases of MS.

Dr. Banwell stressed, however, that multiple sclerosis

is a complex autoimmune disease, and that there are no

doubt a number of triggers. For examples, there is a

lot of research that links MS to lack of exposure to

sunlight.

That could explain why countries farthest from the

equator, such as Canada and Australia, have the

highest rates of MS. That research suggests that lack

of exposure to ultraviolet light, or to vitamin D, may

be a trigger.

Recent research has shown a certain type of cell in

the immune system, called a T helper cell type 1,

leads the attack on myelin, and that exposing the T

helper cells to ultraviolet light can stop those

attacks (at least in laboratory mice).

But another possibility is that people in northern

countries, because of their extreme weather, spend

more time indoors, and are more likely to be exposed

to common viruses such as EBV and herpes simplex.

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