Social Etiquette is pretty standard for this sort of thing.
If you are contagious: As already stated, the other party should be informed and given the chance to choose to avoid infection.
If you are not contagious but still sick/displaying symptoms: This then becomes the same as any other non-contagious illness, where openness is appreciated especially if it starts affecting your life but overall and especially with new partners it is not essential information that needs to be stated immediately. It is still expected that you eventually let them know but it is okay to do it "in your own time".
If you are no longer sick: It is no longer an aspect of your life and there is no expected etiquette to let someone know about your past ailments; perhaps you could bring it up as a point of interest? In your case however, since the vast majority (98% from what I can gather.. please correct if wrong) of adults have had EBV in their lifetime so it would probably be more interesting if you haven't had it.