From New Scientist, 6 January 2010. (Story by Claire Wilson and Ewen Callaway).
The theory that chronic fatigue syndrome could be caused by a virus that jumped from mice to people has been dealt a blow by a British study that has found no evidence of the virus in people diagnosed with CFS.
Scientists are also warning people with the condition of the dangers of dosing themselves with antiretroviral drugs.
CFS affects more than a million people in the US and a quarter million in the UK. Its symptoms include persistent, severe tiredness, but its cause remains mysterious and contentious.
The debate on its origins took a new twist in October, when DNA from xenotropic murine leukaemia virus-related virus (XMRV) was found in the blood of about two-thirds of 101 people with CFS, compared with just 4 per cent of healthy people (Science, DOI: 10.1126/science.1179052). The researchers, led by Judy Mikovits of the Whittemore Peterson Institute in Reno, Nevada, suggested that XMRV might be causing CFS.
Now a second study, led by Myra McClure of Imperial College London, has failed to find XMRV in blood samples from 186 people in the UK with CFS. “We do not share the conviction that XMRV may be a contributory factor in the pathogenesis of CFS, at least in the UK,” McClure's team says.
Mikovits stands by the conclusions in her paper. She suggests that XMRV may be less common in Europe and so might not be causing cases of CFS there.
At least one US lab is offering to test people withh CFS for XMRV, while websites are abuzz with reports from patients who say they have been tested and queries about how to obtaib zidovudine (AZT), the antiretroviral drug used to combat HIV.
In lab experiments reported last month, AZT was found to block replication of XMRV (Virology, DOI: 10.1016/j.virol.2009.11.013). But Richard Baker, head of the group that wrote the official UK guidelines on CFS, warns patients against taking AZT, which can have side effects. “Anyone who uses it on themselves is taking a real risk with their health,” he says. Mikovits says it is unlikely to be effective against CFS.
Other researchers are trying to further establish whether there is a link between XMRV and CFS, but have not yet published the results. There are hints that these results may also be negative.
The Robert Koch Institute (RKI) in Berlin, Germany, is also examining the link between XMRV and CFS. In November, its collaborators posted a short statement on the web saying that CFS patients had so far “rarely” tested positive for the virus. They later removed the statement.
According to Norbert Bannert, one of the virologists at the RKI, the statement was correct, but he adds: “It's not fair to give numbers when you're at the beginning of the investigation, and the first results have not yet been confirmed by an alternative test.” He declines to give further details
McClure has also hinted that several studies due to be published soon have also found no link.
People with CFS who say they have been tested are less restrained. On one online message board, a handful of people have reported mixed results: none of 10 patients who used one company's test said they turned up positive for the virus, while six out of 12 people who took another set of tests offered by another lab said they were positive for XMRV.
If the virus link is not borne out, people with CFS are going to feel seriously disappointed, Shepherd warns. “I think people are going to feel very, very let down to put it mildly,” he says.
Journal reference: PLoS ONE, DOI: 10.1371/journal.pone.0008519