Do viruses cause chronic fatigue syndrome?
The answer isn't clear, but there's more evidence that suggests the idea might not be so far-fetched.
Government scientists found that blood cells from people diagnosed with chronic fatigue syndrome were much more likely than samples from people without the condition to contain traces of genetic code from viruses that cause leukemia in mice.
Eighty-seven percent of samples from CFS patients (32 of 37) contained genetic fingerprints from murine leukemia viruses, which can also infect humans. Only 7 percent (3 of 44) of samples from normal blood donors show signs of the viruses.
The results bolster a controversial report last year that linked a related virus, XMRV, to chronic fatigue. One reason people have thought a virus might be to blame for the debilitating condition is that the symptoms resemble a bad case of the flu that doesn't go away.
The National Institutes of Health's Dr. Harvey Alter, senior author of the paper, said in a conference call with reporters, "It's an association, but that's all it is." He was careful to say the findings don't prove that a virus causes CFS.
The results from the latest study were published online by the Proceedings of the National Academy of Sciences.
Since the Science paper last year that implicated XMRV, other groups have had trouble reproducing the findings, casting doubt on its significance. The latest work didn't find that particular virus either.
Alter says that it's "a dilemma" that some researchers find an association between CFS and a virus while others do have not. He hypothesized that the lack of hardcore standardized test for CFS, such as a biopsy, means that variability in the patients selected for study could be part of the problem.
One way to settle the question would be to test antiretroviral drugs in patients with CFS. The University of Alberta's Dr. Andrew Mason suggested in an accompanying commentary that the benefits of such a study may outweigh the risks. "If the patients improve, after a certain point you stop debating whether [a virus] causes the disease and say the treatment works and we're going to use it," he told the Wall Street Journal.