Herpes Virus Strain Identified as a Trigger in Multiple Sclerosis
Contact: Stephanie Clipper, Marian Emr (301) 496-5751
Source: National Institute of Neurological Disorders and Stroke (NINDS)
November 24, 1997
A strain of reactivated herpes virus may be associated with multiple sclerosis
(MS), an autoimmune disorder in which the body attacks its own tissues.
Results of a study conducted by scientists at the National Institute of
Neurological Disorders and Stroke (NINDS) in Bethesda, Maryland, add to
mounting evidence of the role of viral triggers in MS and may serve as the
cornerstone for clinical trials using antiherpetic agents as a treatment. This
is the first published large-scale study suggesting an association of a human
herpes virus in the disease process of MS.
In the study, more than 70 percent of patients with the relapsing-remitting
form of MS showed an increased immune response to human herpes virus-6 (HHV-6)
and approximately 35 percent of all MS patients studied had detectable levels
of active HHV-6 in their serum. Scientists believe that there may be a point
in time during the progression of MS when the virus, which lies dormant in the
body for years, reactivates, accounting for its presence in a subset of MS
patients. The study appears in the December 1997 issue of Nature Medicine.1
"We expect that currently available antiviral treatments--for example,
acyclovir--might one day be applied successfully to MS," said Steven Jacobson,
Ph.D., Chief of the NINDS Viral Immunology Section and the studyÆs principal
investigator. "WeÆve suspected a possible role for a virus in MS for quite
some time, and these results certainly point to this particular virus. But we
need to know more before we move to the clinical trial stage."
As many as 350,000 Americans are affected by MS, which is most often diagnosed
in patients between the ages of 20 and 40 and is characterized by muscle
weakness, visual disturbances, and a variety of other neurological
impairments. The array and severity of symptoms varies widely from patient to
patient and women are more likely to be affected than men. The most common
form of MS is the relapsing-remitting type. In this type of MS, new symptoms
appear or existing ones become more severe, followed by periods of partial or
total recovery. These flare-ups of new or intensified symptoms last for
variable amounts of time. A second form of MS is a chronic and progressive one
in which symptoms steadily worsen. Either form can lead to disability and
paralysis.
"WeÆve thought for a long time that genetics, an autoimmune factor, or
something in the environment--like a virus--might cause MS," says Dr.
Jacobson. "One can certainly make the case for a combination of these factors,
namely that a small group of individuals may be genetically susceptible to a
virus. If the HHV-6 virus is really behind MS, then we also need to know why
infection with such a common virus causes disease in so few people."
HHV-6 is relatively new to scientists and is known to cause a common childhood
illness, roseola. HHV-6 is known to be present in 90 percent of the adult
American population as a result of infection during the first few years of
life.
Scientists believe that the reactivation of HHV-6 virus may be associated with
the breakdown of the protective covering of nerves, called myelin.
Reactivation is characteristic of herpes viruses.
In the study, investigators screened the serum of 102 individuals, 36 of whom
had MS. Of the 22 individuals with the relapsing-remitting form of MS, 73
percent had an increase in immune response to an early antigen of HHV-6,
compared to only 18 percent of those participants who served as normal
volunteers. In addition, the scientists detected HHV-6 DNA in the serum (a
marker of active virus infection) of 15 of 50 individuals with MS. All 47
individuals without MS tested negative for the presence of active HHV-6 viral
infection.
Additional testing for the presence of HHV-6 virus in larger numbers of MS
patients--and in patients with other autoimmune disorders--is under way.