While chronic fatigue syndrome is now recognized by the medical community as a real illness, treatments have remained elusive, largely because nobody knows what causes the condition, marked by extreme tiredness and weakness most of the time. Now several new studies have dashed hopes that the syndrome might have a viral link—which in turn would have opened the door to better prevention and treatment.

In an article published online Tuesday in the journal Lancet, researchers from the Netherlands summarized the results of three recently published studies that essentially seem to rule out the possibility that a retrovirus called XMRV, or xenotropic murine leukemia virus (MLV)-related virus, is a cause of chronic fatigue syndrome. That possibility was raised by a controversial 2009 study published in the journal Science in which researchers reported finding the virus—previously observed only in animals—in the white blood cells of 67 percent of patients with chronic fatigue syndrome, vs. 3.7 percent of healthy controls. If true, that would have had major implications for treatment of the disorder since patients might have been able to use antiretroviral drugs to fight it.

But the methodology of the research was quickly called into question, and several subsequent studies detected no XMRV in either patients or controls. Other research raised the possibility that the presence of the virus in the original study may have been due to laboratory contamination.

The three new investigations cited in today’s Lancet article “seem to provide the final nail in the coffin” of the retrovirus-CFS theory, according to the authors. Of the new studies, two—including one published in the same journal that originally reported the retrovirus link—failed to detect either XMRV or related viruses in a large sample of patients with chronic fatigue, including patients from the original 2009 study. And they present evidence that the original samples may have been contaminated by mouse DNA. The third study provides further evidence that laboratory contamination, and not infection of chronic fatigue patients with XMRV, accounted for the apparent link between the virus and the disorder.

XMRV is but the latest in a series of infectious agents posited as possible causes for chronic fatigue for which evidence has subsequently turned up empty. “Sadly, we have to conclude that the world has witnessed yet another false claim that gave new hope to patients with CFS, who are desperately seeking a cause for their suffering,” the authors wrote.

Read more about chronic fatigue syndrome and therapies—including graded exercise and cognitive behavioral therapy—that can help.

Sources
XMRV and CFS—the sad end of a story [Lancet]

Detection of an Infectious Retrovirus, XMRV, in Blood Cells of Patients with Chronic Fatigue Syndrome [Science]

No Evidence of Murine-Like Gammaretroviruses in CFS Patients Previously Identified as XMRV-Infected [Science]