Back in 1980s, there were proposals for a "chronic mononucleosis" or "chronic mononucleosis syndrome" as a diagnosis / standard disease. There were very compreh

Back in 1980s, there were proposals for a "chronic mononucleosis" or "chronic mononucleosis syndrome" as a diagnosis / standard disease. There were very comprehensive studies trying to investigate the patients who had chronic fatigue and other long lasting debilitating symptoms. After a good decade of studies, the research community found that this group of patients is very consistent (their complaints, symptoms, etiology), but failed to prove EBV as a cause (although the studies did not disprove it either) or at least come up with a clear serological diagnostic criteria. So, in 1990s they decided to define a generic Chronic Fatigue Syndrome (CFS) as a standardized disease. Other viruses and pathogens can cause CFS/ME and a broader definition would sometimes include even psychosomatic patients, so as a result CFS/ME has been quite discredited. Diagnostic techniques evolved and research progressed. In the recent decade, new studies are very close to proving that EBV is indeed a likely cause of CFS/ME (well, one segment, as there are other causes too). Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7912523/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7912523/