The Epstein-Barr virus (EBV) may cause MS, according to a study published in Science. Kjetil Bjornevik, MD, PhD, and colleagues examined the association between the prevalence of EBV and MS in a cohort of more than 10 million young adults on active duty in the US military. A total of 955 incident MS cases were documented during the periods of service. EBV infection status was assessed in 801 MS cases and 1,566 controls. Dr. Bjornevik and colleagues found that only one MS case occurred in an EBVnegative sample. Thirty-five MS cases and 107 controls were EBV-negative at baseline. During follow-up, all but one of the MS cases became infected with EBV and all seroconverted before MS onset. To examine the temporal relation between EBV and MS, serum concentrations of neurofilament light chain (sNFL) were assessed. Individuals who were EBV-negative at baseline and went on to develop MS had sNFL levels that were similar to those of non-MS controls at the time of EBV infection, but levels increased thereafter.