Viruses have long been suspected as a cause of Chronic Fatigue Syndrome or CFS, but research studies have been mixed, in part because we lack the tools to detect the viruses we suspect.

The sudden onset of CFS in some patients with an “infectious-like” illness, the nature of some of the symptoms, and the state of chronic immune activation suggest that chronic fatiguing illnesses can be triggered and perpetuated by a virus. CFS symptoms have been described in a variety of acute infections (Leventhal et al., 1991; Rosene et al., 1982; Cluff et al., 1959; Salit, 1985.). Many investigators have reported enteroviral infections in CFS (Cunningham et al., 1990; Gow et al., 1991, 1996; Bowles et al., 1993; Clements et al., 1995; Richardson, 1995; Richardson, 1995; Soteriou et al., 1996). Also, a number of studies have suggested that parvovirus can produce CFS (Kerr et al., 2001, 2002; Matano et al., 2003).

A recent observational study has confirmed the existence of a post-infectious fatigue syndrome and provided clues as to its etiology. Hickie and colleagues identified all cases of acute infection with Epstein-Barr virus (a DNA virus),