Chronic fatigue syndrome (CFS) is often referred to by other names or used interchangeably with similar disorders, such as chronic fatigue and immune dysfunction syndrome (CFIDS), fibromyalgia (FM), myalgic encephalomyelitis (ME), Gulf War Syndrome, and chronic Epstein-Barr disease. Recently, the Centers for Disease Control (CDC) has published epidemiologic figures estimating that approximately 800,000 Americans are affected by CFS. The associated economic loss is estimated in the billions of dollars, due to disability, medical expenses, and loss of wages. CFS is an incompletely understood, yet severely disabling disease of unknown etiology. It is characterized by profound, debilitating fatigue, of greater than 6 months duration that cannot be resolved with rest. Associated symptoms include fever, sore throat, myalgias, lymphadenopathy, sleep disturbance, headaches, neurocognitive difficulties (such as memory and concentration impairment and "mental fog''), and symptoms associated with autonomic dysfunction.
Frequently, patients report a sudden onset of CFS symptoms following an acute flu-like illness. CFS was initially thought to be caused by a prolonged viral infection, possibly by Epstein-Barr virus (EBV). However, after extensive study, it became clear that CFS is not caused exclusively by any one viral agent. Instead, CFS might represent a common pathogenic end point, and multiple viruses or other infectious agents might have a contributory role in the onset or persistence of symptoms in CFS (CDC, 2005).
Since the initial reports and the definition of CFS was established by the CDC in 1994, many viruses have been implicated and studied, including enteroviruses, re-troviruses, and the human herpesviruses (HHVs). A substantial body of literature documents the association of HHV-6 with CFS. Some studies examining the relationship between CFS and HHV-6 have produced ambiguous findings. This might be due in part to overly broad selection criteria for the patient sample, small sample sizes, failure to match control subjects with patients, and the use of inappropriate techniques for detecting active HHV-6 infection. Furthermore, because latent HHV-6 infection is nearly universal in adults, only tests that can differentiate between active and latent infection are likely to produce meaningful results. Additionally, early published studies in particular not only failed to differentiate active and latent infection, but they also did not differentiate between HHV-6 variant A or variant B.
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