October 19, 2009

Virus Linked to Chronic Fatigue Syndrome

Transmission electron micrograph of round virus particles XMRV virus particles seen by transmission electron microscopyUniversity of Utah Health Sciences Public Affairs.

Scientists have detected the DNA of a retrovirus in the blood of patients with chronic fatigue syndrome. The discovery raises the possibility that the virus may be a contributing factor in chronic fatigue syndrome.

Chronic fatigue syndrome, or CFS, is a debilitating disease that affects millions of people in the United States. It's characterized by profound fatigue that doesn't improve with bed rest and can be exacerbated or re-kindled by physical or mental activity. A number of other symptoms are also associated with CFS, including cognitive deficits, impaired sleep, myalgia, arthralgia, headache, gastrointestinal symptoms and tender lymph nodes.

No specific cause for CFS has yet been identified. However, patients with CFS are known to have some abnormalities in their immune system. Recently, scientists found evidence of a virus called xenotropic murine leukemia virus-related virus, or XMRV, in the tumors of patients with prostate cancer. Some patients with XMRV-positive prostate cancer were reported to have a specific immune system defect that was also seen in CFS patients. Suspecting a link between the virus and CFS, a team of scientists from the Whittemore Peterson Institute at the University of Nevada, NIH's National Cancer Institute (NCI) and the Cleveland Clinic set out to look for the virus in blood samples.

The scientists identified DNA from XMRV in the blood cells of 68 of 101 (67%) CFS patients, as reported in the online edition of Science on October 8, 2009. In contrast, the blood of only 8 out of 218 healthy people (3.7%) contained XMRV. Blood cells not only contained XMRV DNA, but also expressed XMRV proteins and produced infectious viral particles.

The researchers also found that XMRV stimulates immune responses in people with CFS. Plasma from 9 out of 18 CFS patients infected with XMRV reacted with a viral protein, whereas none of the plasma from 7 healthy donors showed a reaction.

“These compelling data allow the development of a hypothesis concerning a cause of this complex and misunderstood disease, since retroviruses are a known cause of neurodegenerative diseases and cancer in man,” says Dr. Francis Ruscetti of NCI, who worked on the project.

Retroviruses like XMRV have also been shown to activate a number of other latent viruses. This could explain why so many different viruses, such as Epstein-Barr virus, have been associated with CFS.

The researchers cautioned, however, that while this study found an association between XMRV and CFS, further work will be needed to determine whether XMRV truly contributes to the development of CFS.

“The discovery of XMRV in 2 major diseases, prostate cancer and now chronic fatigue syndrome, is very exciting,” says Dr. Robert H. Silverman, a co-author at the Cleveland Clinic. If a role for XMRV is established, there could be new opportunities for prevention and treatment of these diseases.

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