Two new studies say a link between a virus and chronic fatigue syndrome probably was a false alarm caused by laboratory mistakes, yet another blow to sufferers of the mysterious illness who hope that finding a cause will lead to a cure.
The journal Science took the unusual step Tuesday of declaring the virus link "seriously in question," making it the latest potential culprit that could fall by the wayside.
In a headline-making discovery, Nevada researchers in 2009 announced they'd found traces of a mouse-related virus in the blood of a number of patients with chronic fatigue, an illness thought to afflict about 1 million Americans. The finding fueled hope that a cause might finally have been found even as it led blood banks to turn away donations from chronic fatigue patients _ and prompted some patients to try out anti-viral medicines normally used for HIV.
Doubt already was growing among many other scientists, as numerous other studies failed to find any connection between the purported infection and human illness.
Now the newest research, published by Science Tuesday, says the link with the virus named XMRV almost certainly was a result of laboratory contamination and doesn't pose a risk to humans.
"I see right now no good reason to believe that this specific virus actually ever infects humans," said Dr. John Coffin, a Tufts University professor and National Cancer Institute special advisor who co-authored one of the studies.
The new findings are particularly important for patients using anti-viral drugs, added Dr. Jay Levy of the University of California, San Francisco, who led the second study.
Those drugs "are not totally harmless. They should be off those drugs," he said.
Scientists first uncovered XMRV several years ago not in chronic fatigue patients but in some men's prostate tumors.
Here's why that matters: The NCI used sophisticated genetic tracing to show the XMRV virus was created when two other mouse viruses combined during some experiments about a decade ago that involved growing human prostate tumors in the animals. That virus' genetic fingerprint so closely matches what was later found in samples taken from patients, that it's extremely unlikely the XMRV could have come from another source, Coffin explained.
Batches of cells and other lab products are so widely shared that it's very easy for contamination from mouse viruses and mouse DNA to persist years later, and in multiple labs, he said.
In the second study, Levy's team tested new blood samples from the same chronic fatigue patients used to make that first 2009 link with XMRV. This new testing, which avoided using lab products derived from mice, found no evidence of XMRV, further supporting the lab-contamination explanation.
In fact, substances in human blood can kill the mouse-related virus, Levy said. He argued it's time to move on, saying there's evidence that chronic fatigue involves an immune disorder: "Let's use the money to find the real culprit."
But the controversy isn't over. The Nevada researchers who first announced a possible link defended their findings and said critics haven't looked for the new virus the way they did.
In a letter to Science, Dr. Judy Mikovits of Nevada's Whittemore Peterson Institute said retracting the findings would be premature and "have a disastrous impact on the future of this field of science."
The National Institutes of Health already had begun still other, more rigorous studies to settle the issue.
The Chronic Fatigue and Immune Dysfunction Syndrome (CFIDS) Association of America said Tuesday's work is "the result of diligent effort by top experts" but that it awaited the final NIH studies.
Various viruses have been linked to chronic fatigue over the years, only to be ruled out as potential culprits. Chronic fatigue is characterized by at least six months of severe fatigue, impaired memory and other symptoms, but there's no test for it _ doctors rule out other possible causes _ and no specific treatment.