UK scientists say they can find no proof that a particular virus is the cause of chronic fatigue syndrome (CFS) or ME, contrary to recent claims.

Scientists at Imperial and King's universities in London have attempted to replicate work carried out in the US and published in the journal Science last October. But they found not one of the 186 patients they studied had a trace of the novel virus, called XMRV, in their blood samples.

The theory, which made headlines around the world last October, gave hope to many. About three in every 1,000 people, possibly more, suffer from chronic fatigue syndrome (CFS), formerly known as myalgic encephalomyelitis (ME), which is a condition described one of the authors of the paper, Dr Anthony Cleare, reader in psychiatric neuroendocrinology at King's, as serious and debilitating and extremely frustrating for sufferers who do not know its cause.

The study in Science, by Vincent Lombardi and colleagues at a small private pathology laboratory in Reno, Nevada - the Whittemore Peterson Institute - sent many patients hurrying to doctors for tests and antiretroviral drugs.

Lombardi and his team reported that they had found the virus XMRV in 67% of the CFS patients they tested. Later they said they had found it in 95% of patients. Lombardi has devised and sells a test for the virus in north America.

Scientists around the world embarked on their own tests, and Dr Cleare and his colleagues are the first to publish results. "If this research is replicated, it is potentially a huge breakthrough in understanding this condition," he said.

The UK Test

King's College hospital runs a specialised CFS/ME clinic. The researchers selected blood samples from 186 patients who were, they said, typical of those who attend. They had suffered for years, were very disabled by the disease and more than 90% said their illness definitely or probably started after a viral infection.

They sent the samples to a team at Imperial's retrovirology labs. Professor Myra McClure, from the division of medicine at Imperial College London and one of the authors of the study published today by PloS One (Public Library of Science), said: "Our research was carried out under rigorous conditions. We used very sensitive testing methods to look for the virus. If it had been there, we would have found it.

"The lab in which we carried out the analysis had never housed any of the murine leukaemia viruses related to XMRV, and we took great care to ensure there was no contamination. We are confident our results show there is no link between XMRV and CFS, at least in the UK." The authors say there is no evidence to justify testing people with CFS for the virus or putting them on drug treatment.

Reactions To The UK Results

Whittemore Peterson Institute

In the wake of the British findings, a statement was later issued on behalf of the Whittemore Peterson Institute. It stated: "This study did not duplicate the rigorous scientific techniques used by WPI, the National Cancer Institute and the Cleveland Clinic, therefore it cannot be considered a replication study nor can the results claim to be anything other than a failure not just to detect XMRV, but also a failure to suggest meaningful results."

The WPI statement went on to say, "The scientific methods used by WPI are very exact and require specific techniques to ensure accuracy. Differences in techniques employed by Erlwein et al. not only explain their failure to replicate the WPI study, but also render the conclusions meaningless. These differences include, but are not limited to the following:

1. blood sample volumes and processing
2. patient criteria/population differences
3. number and type of tests done to assure accurate results, including white blood cell culture
4. use of a molecular plasmid control in water versus a positive blood sample
5. different primer sequences and amplification protocol used to find the virus, which were not validated by a clinical control

The WPI study was published after six months of rigorous review and three independent lab confirmations, proving that contamination had not taken place and that infectious XMRV was present in 67 percent of CFS patients diagnosed according to the Canadian and Fukuda criteria. In contrast, this latest study was published online after only three days of review. Significant and critical questions remain as to the status of patient samples used in the UK study as those samples may have been confused with fatigued psychiatric patients, since the UK has relegated 'CFS' patients to psychiatric care and not traditional medical practices."

Professor Myra McClure

Professor Myra McClure, one of the Imperial College London investigators, said: "We are confident that our results show there is no link between XMRV and chronic fatigue syndrome, at least in the UK."

She said they had used extremely sensitive DNA testing methods, called polymerase chain reaction, to look for the virus. "If it had been there, we would have found it."

Co-author Professor Simon Wessely

Co-author Professor Simon Wessely said the findings did not invalidate all previous research, some of which has shown that CFS can be triggered by other infectious agents, such as Epstein Barr Virus.

Action for ME

The charity Action for ME said it was disappointing to hear about these findings, but said no single small-scale study could be conclusive.

Dr. Charles Shepherd, of The ME Association

Dr. Charles Shepherd, of The ME Association, said it was important to remain open-minded. "We need to be extremely cautious until we know more. There has been enormous interest in this from patients. Some have been led into believing the cause and a test has been discovered and that treatment is just round the corner and that is not the case. Over the next few weeks and months we will have more results and then we can come to a conclusion. If it turns out that XMRV is important, we will have to start looking at whether it is worthwhile testing for it and treating it."

Dr Judy Mikovits from the Whittemore Peterson Institute

Dr Judy Mikovits from the Whittemore Peterson Institute said: "Little is known about the prevalence of XMRV worldwide, much less the incidence of XMRV in ME/CFS or prostate cancer.

She added more study was needed and they were collaborating with international research teams to unpick the questions around the virus.

Invest in ME

In a statement, the charity Invest in ME said the original Science study was of the "highest quality", and that much more work was required before any firm conclusions could be drawn.