June 1, 2011

Mouse Virus Not Linked To Chronic Fatigue Syndrome

A 2009 study that suggested chronic fatigue syndrome was caused by a mouse virus has been challenged by a recent study that claims the results were based on contaminated lab samples.

"There is no evidence of this mouse virus in human blood," says lead author of the current study Jay Levy of the University of California at San Francisco.

In 2009, Nevada researchers announced a headline-making discovery that linked a mouse-related virus to a number of patients with chronic fatigue syndrome, giving hope to millions that the cause may have finally been found.

Chronic Fatigue Syndrome is considered a mysterious illness that affects an estimated 1 to 4 million Americans. The symptoms range anywhere from muscle pain to insomnia to memory loss as well as overwhelming fatigue, leaving many with a significantly diminished capacity for physical or mental activity for years without any relief.

Researchers from the 2009 study reported findings traces of a mouse-related virus called xenotropic murine leukemia virus-related virus (XMRV) in two-thirds of the blood samples taken from 101 patients with chronic fatigue syndrome.

The virus was shown to be capable of infecting human cells grown in the laboratory.

"It gave great encouragement to Chronic Fatigue Syndrome patients," Levy says. "Many believed that the cause had finally been found."

The 2009 study led to some patients being treated with anti-viral drugs similar to those used against HIV/AIDS, making the new findings important for patients on these anti-viral drugs.

"Individuals with Chronic Fatigue Syndrome need to know that taking antiretroviral therapies will not benefit them, and may do them serious harm," says co-author Konstance Knox of the Wisconsin Virus Research Group in Milwaukee, Wisconsin.

He also says, "Physicians should not be prescribing antiviral compounds used in the treatment of HIV/AIDS to patients on the basis of a Chronic Fatigue Syndrome diagnosis or a XMRV test result."

The current study was conducted shortly after the 2009 study was published, when one of its authors contacted Levy to help confirm the findings by taking a look at other blood samples taken from patients with the illness.

Blood samples from 61 patients with Chronic Fatigue Syndrome were examined by Levy for the current study. Forty three of which were previously reported as being infected with the mouse-related virus XMRV. Using similar procedures to the 2009 study, Levy and his colleagues were not able to find evidence of XMRV or any other mouse-related virus.

Levy's team also determined that it was very unlikely that humans could become infected with the mouse virus because "human serum quickly kills it."

Levy and his colleagues hypothesize that the original traces of XMRV found in the 2009 study probably came from common laboratory reagents or cell lines used in the original experiments.

"With this extensive study, we could not confirm any of the results of the earlier papers," says Levy.

Even though XMRV is not the cause of Chronic Fatigue Syndrome, it is possible that some infectious agent could be involved, he says.

"Work should continue to find it," he says.

These findings, along with follow up research from other scientists should help put the controversy to rest, however, the Nevada researchers in the 2009 discovery defend their findings, saying that critics haven't looked for the new virus the way they did.

Dr. Judy Mikovits of Nevada's Whittemore Peterson Institute says that retracting the (2009) findings would be premature and "have a disastrous impact on the future of this field of science."

The National Institutes of Health (NIH) hopes to settle the issue by conducting yet another, more rigorous series of studies.

The Chronic Fatigue and Immune Dysfunction Syndrome (CFIDS) Association of America say that the new study is "the result of diligent effort by top experts," but that it will wait for the final NIH studies.

The recent study is published in the journal Science on Tuesday.


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