Viral studies of chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) has many characteristics suggesting persistent fatigue following a viral illness. At least nine different RNA and DNA viruses have been considered to be associated with this disease, but none of these viruses has been found to be the etiologic agent. Immunologic studies have demonstrated activated CD8+ cells and reduced function of natural killer cells suggesting a host response to an infection that has led to persistent immune disorders. Some of the symptoms of CFS may be due to cytokines produced by this hyperactive immune response to a virus that is still present in the host or that has been eliminate but leaves abnormal immunologic sequelae. These possibilities offer directions for future studies of CFS and therapeutic approaches to this condition.