"Researchers believe [ME/CFS] will ultimately prove to have multiple causes, including genetic predisposition and exposure to microbial agents, toxins and other physical and emotional traumas.  Studies have linked the onset of chronic fatigue syndrome with an acute bout of Lyme disease, Q fever, Ross River virus, parvovirus, mononucleosis and other infectious diseases".  (New York Times, "Chronic Fatigue No Longer Seen as 'Yuppie Flu'", David Tuller, July 17, 2007)

Dr. Joseph Montoya, a Stanford infectious disease specialist, believes there is a link between ME/CFS and Epstein Barr Virus as well as HHV-6.

As I post this (February 2009) it is encouraging to know that research has begun, but to my knowledge there are no conclusive studies that reveal for certain the cause of ME/CFS.