Multiple sclerosis (MS) is a chronic autoimmune disease that impacts nearly 3 million people around the world. The cause of the disorder is unclear, though it's been suggested that genetics, environmental conditions, and the microbiome could play a role. Now, researchers have found evidence that a virus may be to blame. Epstein-Barr virus is a common type of herpes virus that often doesn't cause illness, but can cause mononucleosis, and may remain dormant in a host for their lifetime.
Reporting in Science, investigators performed a study that included health data from over 10 million people who were on active military duty. This massive amount of information enabled them to decipher the links between MS, which is not very common, and Epstein-Barr virus (EBV), which is thought to have infected about 95 percent of people. Within the dataset were 955 people who were diagnosed with MS while they served in the military.
Samples of serum that had been collected by the military once every two years were analyzed. These samples revealed when individuals had been infected with EBV, and if it was prior to the first sample collection. For those who had been infected, their risk of developing MS was increased 32 times; all but one of the people diagnosed with MS carried EBV antibodies. Notably, But, MS risk was unaffected by infection with other viruses.
Neurofilament light chain is used as a biomarker that indicates whether MS-related nerve degeneration is occurring. The researchers found that neurofilament light chain levels only increased after an EBV infection. The study authors noted that nothing else we know about MS can explain this finding, suggesting that EBV is causing MS.
For some people, MS symptoms begin around ten years after EBV infection occurs. The symptoms of MS may start out mildly and not be detectable at first, which could explain why there is such a long delay between EBV infection and MS diagnosis, or, the delay may be due to the interaction between the virus and the host's immune system, suggested Ascherio.
While several research groups have been studying the link between MS and EBV "this is the first study providing compelling evidence of causality," said the senior study author Alberto Ascherio, a professor of epidemiology and nutrition at Harvard Chan School.
For some people, MS symptoms begin around ten years after EBV infection occurs. The symptoms of MS may start out mildly and not be detectable at first, which could explain why there is such a long delay between EBV infection and MS diagnosis, or the delay may be due to the interaction between the virus and the host's immune system, suggested Ascherio.
While treatments for MS have improved in recent years, patients have to manage a complex set of symptoms, and that management lasts a lifetime. This work indicates that it may be possible to prevent MS from developing by halting EBV infection, and "targeting EBV could lead to the discovery of a cure for MS," added Ascherio.
Right now, we don't have a way to prevent or eliminate EBV infections, Ascherio noted, "but, an EBV vaccine or targeting the virus with EBV-specific antiviral drugs could ultimately prevent or cure MS."