Causes

Infections

Because most of the features of CFS resemble those of a lingering viral illness, many researchers have focused on the possibility that a virus or some other infectious agent causes the syndrome in some cases. There are three basic theories for infection-related causes of CFS:

• One theory referred to as "hit and run" suggests that chronic fatigue syndrome might be the result of a virus or bacteria that infects the body, causes immune abnormalities, and is then eliminated. It leaves behind a damaged immune system, however, that continues to cause flu-like symptoms even in the absence of the virus.
• Another theory posits that an abnormal immune response reactivates a virus that had persisted in a latent (inactive) stage after an initial infection.
• A psychological response to viral infections occurs in susceptible individuals.

Still, not all CFS patients show signs of infection. While experts have long been divided on whether infections play any role in this disorder, subtypes of viral-related and non-viral CFS may both exist.

Viruses. The theory that CFS has a viral cause is not based on hard evidence but on various observations that suggest an association, such as the following:

• CFS patients typically have elevated levels of antibodies to many organisms that cause fatigue and other CFS symptoms. Such organisms include those that cause Lyme disease, candida ("yeast infection"), herpesvirus type 6 (HHV-6), human T cell lymphotropic virus (HTLV), Epstein-Barr, measles, coxsackie B, cytomegalovirus, or parvovirus. Many of these infectious agents are very common, however, and none has emerged as a significant cause of CFS.
• In up to 80% of cases, chronic fatigue syndrome starts suddenly with a flu-like condition.
• In the U.S., there have been reports of cluster outbreaks of CFS occurring within the same household, workplace, and community (but most have not been confirmed by the U.S. Centers for Disease Control and Prevention).
• Some researchers are suggesting that changes in normally harmless bacteria found in the intestine may play a role in the development of CFS symptoms.