From BBC Online, 9 October 2009
US scientists say they have made a potential breakthrough in understanding what causes the condition known as chronic fatigue syndrome (CFS) or ME.
Their research in the journal, Science, suggests that a single retrovirus known as XMRV does play a role in ME.
They found the virus in 67% of ME patients compared to under 4% of the general population.
But experts cautioned that the study did not conclusively prove a link between XMRV and ME.
ME is a debilitating condition that affects an estimated 17 million people worldwide.
The discovery raises hopes of new treatments for the condition.
Retroviruses are known to cause neurological symptoms, cancer and immunological deficiencies.
The Whittemore Peterson Institute in Nevada, said they had extracted the DNA from XMRV in the blood of 68 out of 101 patients with the condition.
Cell culture experiments revealed that the patient-derived XRMV was infectious.
The researchers said these findings raise the possibility that XMRV may be a contributing factor to ME.
XMRV is also known to have a role in some prostate cancers.
Dr Judy Mikovits, who led the study, said: "It's a blood borne pathogen that we contract through body fluids and blood transmission.
"The symptoms of ME – chronic fatigue, immune deficiencies, chronic infections – are what we see with retroviruses.
"This discovery could be a major step in the discovery of vital treatment options for millions of patients."
Tony Britton, of the ME Association said: "This is fascinating work – but it doesn't conclusively prove a link between the XMRV virus and chronic fatigue syndrome or ME.
"Many people with ME/CFS say their illness started after a viral infection, and a number of enteroviruses and herpes viruses have also been implicated in the past.
"ME/CFS is an immensely complex illness, with many possible causes and there are up to 240,000 sufferers in the UK desperate to get better."