A recently completed British study calls into question a 2009 study that found a link between chronic fatigue syndrome (CFS) and a virus known as xenotropic murine leukemia virus−related virus (XMRV).
The current study tested blood and blood serum samples from 170 people with chronic fatigue syndrome and 395 healthy people. It found no association between CFS and the XMRV virus. A 2009 study had found the virus present in nearly two−thirds of chronic fatigue patients tested.
According to the current official U.S. definition of CFS, a person needs to have unexplained fatigue for at least six months plus at least four of eight other symptoms to qualify as a CFS sufferer.
The British researchers offer no explanation for why the viral link was seen in the 2009 study. They do point out that their test for the virus is much more sensitive than the earlier test was.
The term chronic fatigue syndrome was first proposed in 1988. At first, there was disagreement among medical professionals as to whether CFS even existed or was imaginary. Now, there is broad agreement that it exists but no consensus as to whether it is one disease or several different ones. Possibly the most succinct description of CFS is extreme fatigue that is not the kind of tired feeling that goes away after you rest. According to the current official U.S. definition of CFS, a person needs to have unexplained fatigue for at least six months plus at least four of eight other symptoms to qualify as a CFS sufferer.
A viral cause for CFS has been proposed for many years. The 2009 study excited many people because it was the first one with good evidence for such a link. The current British study calls this link into question. However, even the British study authors accept the possibility that a link may ultimately be shown between XMRV and chronic fatigue syndrome. There's simply too little known about CFS right now to be sure of anything. Or, as the researchers put it: "There has been much discussion and controversy amongst chronic fatigue syndrome researchers and patients alike, which highlights the need for additional investigations in this area."
The Mayo Clinic provides a summary of what is currently known about CFS and how to treat it. While CFS sufferers may not find this information particularly satisfying, right now it's pretty much all the information there is.
An early version of an article detailing the British study was published online on Feb 15, 2010 by the journal Retrovirology.