Multiple Sclerosis May be Linked to Infection
November 27 2002
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Despite decades
of research, the cause of multiple sclerosis remains unknown.
In the past it was suggested that the disease might be immunological,
though more recently it is thought that it could be a genetic
disease.
One theory that
has remained strong over the years is that of viral infections
as a cause. Infections most under suspicion include measles,
rabies, scrapie-like agent, Carp agent, paramyxovirus, coronavirus,
Epstein-Barr virus, herpes zoster, herpes simplex virus, human
herpesvirus 6, rubella, mumps, canine distemper, Marek's Semliki
forest virus, animal and human retroviruses, and human T cell
lymphoma virus type I.
Scientists have
also focused on chlamydia pneumonia and the Epstein-Barr virus
as it was found that patients with multiple sclerosis had
an increase in respiratory infections before the onset of
the disease. However, it is unknown whether the Epstein-Barr
virus plays a specific role in multiple sclerosis or is an
indication of an immune system response in patients with the
disease.
A vascular theory
for multiple sclerosis has also been discussed, along with
dietary therapies, which have a vascular defect as part of
the rationale.
It has been suggested
that vascular changes may precede the inflammation and demyelination
in a multiple sclerosis plaque. Those that advocate the infection
theory believe that an infection could be the initial event
that brings on this process.
In terms of the
genetic factor of the disease, research has shown that siblings
and fraternal twins have a greater risk, by about two to five
percent, than the general population. In identical twins,
this risk is about 30 percent higher. While this seems to
support the genetic proponent, the question has been raised
of why all genetically disposed individuals do not get the
disease. To explain this, researchers say that multiple sclerosis
may be determined by multiple genes and an environmental factor,
possibly infection.
One common theory
holds that genetics, viral infections, and immune reactions
all play a role in multiple sclerosis.
British
Medical Journal 2002;325:1128