Scientists have long searched for the cause of multiple sclerosis, or MS, a disease that damages the brain and spinal cord.
A major study led by researchers at Harvard University found powerful evidence that infection with the Epstein-Barr virus, or EBV, plays a key role in triggering the disease.
MS happens when the body’s immune system attacks myelin, the protective material that surrounds nerve fibers. When this covering is damaged, messages traveling between the brain and the rest of the body can slow down or become disrupted.
People with MS may experience extreme tiredness, weakness, numbness, vision problems, poor balance and difficulty walking. Symptoms vary greatly from person to person, and some people eventually develop lasting disability.
Scientists have suspected EBV for many years because the virus has been linked with MS in earlier research. EBV is extremely common and is best known for causing infectious mononucleosis, sometimes called mono or the kissing disease.
After a person catches EBV, the virus remains in the body for life. Around 95% of adults have been infected, but only a small number develop MS, which has made it difficult to prove whether EBV actually helps cause the disease.
To investigate the question, the Harvard researchers used health information from more than 10 million young adults who served in the U.S. military. Blood samples had been collected from service members repeatedly, allowing the scientists to see when people became infected with EBV.
During the study period, 955 people were diagnosed with MS. The researchers compared their blood samples with samples from people who did not develop the disease and looked at what happened before the MS diagnosis.
The results showed a striking pattern. After EBV infection, the risk of developing MS increased about 32-fold, while infection with other viruses examined in the research did not produce a similar increase.
The team also looked for signs that damage to the nervous system had begun. After EBV infection, levels of neurofilament light chain rose in people who later developed MS.
Neurofilament light chain is a protein released when nerve cells are injured. Finding higher levels after EBV infection suggests that the biological process leading to MS may begin after a person catches the virus, even though obvious symptoms may not appear until years later.
The long delay between EBV infection and MS may help explain why the connection has been so difficult to establish. It may take years for immune changes and nerve damage to build to the point where a person notices symptoms and receives a diagnosis.
The findings do not mean that everyone infected with EBV will develop MS. Because EBV is so common and MS is relatively rare, other factors, including genes and environmental influences, are also likely to affect who eventually develops the disease.
Still, the discovery could point researchers toward new ways to prevent MS. An effective vaccine that prevents EBV infection might reduce future cases, while medicines that target the virus could potentially become part of new treatment strategies.
The research was led by Dr. Alberto Ascherio and colleagues at Harvard T.H. Chan School of Public Health and was published in the journal Science. The study provides some of the strongest evidence so far that EBV is not simply associated with MS, but may be an important trigger of the disease.
For the millions of people affected by MS worldwide, the finding gives scientists a clearer target. Future studies will need to determine exactly how EBV changes the immune system and whether stopping or controlling the virus can prevent MS or improve treatment.
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