You can definitely be infected with EBV and never know it. I've tested positive for the bug, and I never had mono. In many cases, EBV infection is asymptomatic, or can be mistaken for cold or flu.

This is not the first study to show universal EBV infection in MS patients. Prevailing thought is that all MS patients are infected with EBV. My own neurologist, a major researcher here in New York City, told me this several years ago. This study bears out his claim.