Chronic fatiguing illnesses following well-documented infections and acute "infectious-like" illnesses of uncertain cause have been reported for many decades. Chronic fatigue syndrome (CFS) was first formally defined in 1988. There is considerable evidence that CFS is associated with abnormalities of the central and autonomic nervous systems. There also is evidence linking several infectious agents with CFS, although no agent has been proven to be a cause of the illness. Most of the infectious agents that have been linked to CFS are able to produce a persistent, often life-long, infection and thus are a constant incitement to the immune system. Most also have been shown to be neuropathogens. The evidence is consistent with the hypothesis that CFS, in some cases, can be triggered and perpetuated by several chronic infections that directly or indirectly affect the nervous system, and that symptoms are a reflection of the immune response to the infection.

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