I think EBV is going to be a major (but probably not the only) player in ME/CFS. The original studies that showed that EBV could not be the cause of ME/CFS concluded that because many patients did not have active EBV infections (as far as they could tell) and some had never even been exposed -- that is, they had not antibodies to it of any kind. While such research can be very convincing from one point of view -- if some patients had never been exposed, how could EBV be the cause -- there are a lot of questions that give rise to whether or not EBV is a major factor. It's not clear that the patient set they used was exclusively ME/CFS patients. If a significant number of people with other fatigue conditions were included (as they likely were) then it's possible they were the ones without infections. Also, it has been shown since that time that antibody titres are not absolutely accurate in identifying chronic herpesvirus infections. For a completely different perspective -- herpesvirus infections (EBV, HSV-1, HHV-6, CMV...) are always a concern in cases of immune deficiency because they can reactivate fairly easily if the immune system is not in peak condition. So while herpesviruses may be a major player in ME/CFS, they may be secondary to some primary (or even secondary itself) immune dysfunction. Way too many questions, and way, way too few answers.