A new study published in Science by Harvard Medical School researchers suggests that the demyelinating neurodegenerative disease multiple sclerosis (MS) is a complication of Epstein-Barr virus (EBV) infection.

The groundbreaking findings, backed by a massive dataset culled from two decades of U.S. military personnel, mark the culmination of years of circumstantial evidence between EBV, an endemic and latent infection found in up to 95 percent of the population, and the beginning of MS.

MS is a rare but debilitating neurological condition that is thought to impact approximately one million people in the United States. Multiple sclerosis patients have an overactive immune system that eats away at the protective layer of our neurological system, known as myelin.

Lack of myelin slows down and weakens the connections between our brain and body over time, resulting in numbness, muscle weakness, discomfort, and difficulty walking among other symptoms.

Following the initial flare-up, MS evolves differently from person to person, and most people will avoid symptoms and clear neurological damage for months or years between relapses. However, roughly 10% to 20% of people with multiple sclerosis have to live with continual and often worsening symptoms, and some people with relapsing multiple sclerosis will eventually go out of remission.

People lose their ability to write, speak, and walk in the most severe cases, and even the ordinary sufferer has a lower life expectancy.

"The key finding is that MS is a complication of infection with EBV," study senior author Alberto Ascherio, a professor of epidemiology and nutrition at Harvard's T.H. Chan School of Public Health, said.

"MS has been considered for many years an autoimmune disease of unknown etiology. I think this study establishes that this immune process that leads to brain damage is driven by infection with EBV."

For many years, the link between MS and EBV has been postulated, but no definitive study has been able to show a firm causative association. While the vast majority of healthy persons had prior EBV infection, the percentage for MS patients is significantly higher - 99.5 percent of this group tests positive. According to Ascherio, this new study strongly shows that link.

If EBV is the primary cause of MS, then the disease might be avoided by preventing EBV infection, such as using a vaccine, according to the researchers. Targeting the virus with EBV-specific medications could lead to improved disease therapy.

It wouldn't be the first time a vaccine for a germ was designed to prevent a separate but related ailment in the future. In the initial women who received it, the HPV vaccine is already preventing many cases of cervical cancer.