Chronic Fatigue Syndrome Linked to Mouse Virus in U.S. Government Study

Fresh evidence linking chronic fatigue syndrome to a family of mouse viruses was reported in a U.S. government study that has spurred new debate over how to treat the disease.

Almost 90 percent of patients with chronic fatigue syndrome showed signs of infection with a group of mouse leukemia viruses in the study, raising more questions about the cause of the debilitating condition. The results suggest antiviral drugs, including Merck & Co.’s Isentress and Gilead Sciences Inc.’s Viread, should be tested for the condition, French researchers said in an accompanying editorial.

The study, published yesterday in the Proceedings of the National Academy of Sciences, bolsters findings from a year ago that linked the condition to a related infectious agent, called XMRV. The results, though, are contrary to a report by the U.S. Centers for Disease Control and Prevention last month that failed to find a viral link.

“There was a dramatic association with chronic fatigue syndrome, but that’s all it is,” said Harvey Alter, senior author and chief of clinical studies of the department of transfusion medicine at the National Institutes of Health. “We have to emphasize we have not proven causality.”

Chronic fatigue syndrome affects more than 1 million Americans, mainly women, according to the Atlanta-based CDC. There is no cure, and no medicines are approved to treat it. Counseling, antidepressants, behavioral therapy and pain drugs are offered to people with the condition, a CDC website says.

Mouse Virus

The viruses in today’s study are called MLV for murine- related leukemia, a form of an infectious agent known to cause leukemia and other cancers in mice. Researchers at the NIH, the Food and Drug Administration and Harvard Medical School in Boston reported today they found them in blood samples that were taken from 32 of 37 patients with the syndrome about 15 years ago. A repeat test taken this year on 8 of the patients found a slightly mutated form of the virus in 7 of them.

The agents were also discovered in three of 44 samples from healthy blood donors.

The researchers said they didn’t know how the people were infected. There is no evidence, though, that they were transmitted by transfusions or that they lead to other human diseases, said Celia Witten, director of the FDA’s Office of Cellular, Tissue and Gene Therapies, who oversees the lab where the research was conducted.

Dilemma Over Results

The conflict in findings between the latest report and the previous CDC research creates a dilemma for researchers, said Alter, a senior author of the report. One explanation may be that chronic fatigue syndrome is caused by a virus in some and not in others, he said. It’s also possible that people with the condition are more vulnerable to infections, the researchers said.

“That still has to be sorted out,” Alter said in a conference call with reporters.

Additional work is under way to make sure investigators are using the same methods to check for the viruses, and to confirm the results in a wider and more varied group of patients, the researchers said.

It was the first time these specific viruses were found in people or in the blood supply, according to Witten. Another study of 1,000 blood donors is nearing completion to see if the virus or antibodies to it are in the blood supply, Alter said.

Testing Antiviral Drugs

While there isn’t sufficient proof that the mouse viruses cause chronic fatigue syndrome, a study showing whether antiviral drugs are an effective treatment may help confirm the hypothesis, said the doctors led by Valerie Courgnaud, from the University of Montpellier in France, in the editorial.

The new virus and the XMRV virus implicated in the initial study last October are retroviruses, which insert themselves into the genome of the cells they infect in order to multiply. The same approach is used by HIV, the virus that causes AIDS, leading some researchers to test drugs for that deadly disease against chronic fatigue.

Merck’s Isentress fought XMRV more powerfully than 44 other anti-HIV compounds in laboratory tests, according to an April study from researchers at Emory University and the University of Utah.

There are no specific tools to pinpoint chronic fatigue syndrome, which is typically diagnosed after patients experience extreme fatigue for at least six months. The condition is marked by a relapse of symptoms after mental or physical exertion, sleep that doesn’t refresh, and joint and muscle pain.

Previous Report

The link between chronic fatigue and the retroviruses was identified previously by a team led by Vincent Lombardi of the Whittemore Peterson Institute for Neuro-Immune Disease, in Reno, Nevada, and published in October in the journal Science.

Those researchers analyzed the genes in tissue samples collected from 101 patients with chronic fatigue, and found evidence of the mouse virus XMRV in 68 of those studied. The virus was also identified in some prostate-cancer patients.

“These results do raise as many questions as they answer,” said Steve Monroe, director of the CDC’s division of high-consequence pathogens and pathology, in a conference call. “The different findings from different labs show there are a lot of things about this virus we don’t know.”

The research was funded by the National Institute of Allergy and Infectious Diseases and the De Young Foundation.

To contact the reporter on this story: Michelle Fay Cortez in Minneapolis at mcortez@bloomberg.net

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