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Evidence for the role of a virus in MS

The cause of MS is still unknown. However, several factors suggest that an infectious agent is involved in triggering MS.

  • The identical twin of someone with MS, who shares virtually all the same genes, has only a one in four chance of developing the disease — which suggests that factors other than genetics  are involved.

  • Data from epidemiological studies (studies that analyze the geographical, socioeconomic, genetic and other factors that may contribute to who gets MS) suggest that exposure to an infectious agent may be involved in triggering the disease.

  • Ninety to ninety-five percent of people with MS have proteins in their spinal fluid that are typically found in the spinal fluid of people with nervous system diseases that are known to be reactions to viruses.

To date, researchers have not been able to identify a single virus as the trigger for MS. Several viruses have been studied, but multiple steps are required in order to show that a particular virus causes MS. Researchers must prove that:

  • the virus is in the body before MS develops, and

  • the virus actually causes the disease and is not just happening alongside the disease.

The case for Epstein-Barr virus (EBV)

Several studies by Alberto Ascherio, MD, DrPH, and his team at the Harvard School of Public Health have suggested that EBV is involved in MS. The studies found that:

  • Antibodies (immune proteins that indicate a person has been exposed) to EBV were significantly higher in people who eventually developed MS than in control samples of people who did not get the disease.

  • MS risk increased significantly following infection with EBV, thereby demonstrating that EBV was in the body before MS developed.

  • People with a specific immune-related gene and high levels of antibodies to EBV in their blood were nine times more likely to develop MS than those without the gene and with low levels of the antibodies.

  • Current or previous smokers with the highest levels of EBV antibodies were 70 percent more likely to develop MS than those with neither risk factor.

Human herpes virus 6 (HHV-6)

HHV-6 may also be involved in MS — specifically related to triggering relapses. Steve Simpson, PhD, and colleagues at the Universities of Tasmania and Melbourne have found that HHV-6 antibodies were associated with a higher risk of relapse. Also, antibody levels were nearly three times higher in women with progressive MS. These researchers suggest that tracking HHV-6 antibodies may help to predict the clinical course of MS.

Next steps in identifying the role of viruses in MS

Advances in technology are helping MS researchers look for viral clues.

  • John Kriesel, MD and his colleagues at the University of Utah are using a powerful genetics technology that may be able identify other viruses that have not previously been associated with MS.

  • Stephen Miller, PhD and his colleagues at Northwestern University are investigating the idea that perhaps it’s not a virus itself that causes MS, but some immune response triggered by viruses.

  • Emmanuelle Waubant, PhD (University of California at San Francisco) and colleagues around the country are following children who have early MS or are at high risk for the disease for four years in order to determine how viruses and other environmental and genetic risk factors make children susceptible to developing MS. The results from these children will be compared to those of children without MS.

These and other studies are getting us closer to determining what causes MS by identifying triggering factors, thereby increasing the possibility of preventing MS.

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