Retrovirus found in chronic fatigue sufferers
A virus linked to prostate cancer also appears to play a role in chronic fatigue syndrome, according to US research.
The discovery, published in the journal Science, could lead to the first drug treatments for a mysterious disorder that affects 17 million people worldwide.
Researchers found the virus, known as XMRV, in the blood of 68 out of 101 chronic fatigue syndrome patients. The same virus showed up in only 8 of 218 healthy people.
Dr Judy Mikovits of the Whittemore Peterson Institute in Nevada and colleagues at the National Cancer Institute and the Cleveland Clinic emphasise that the finding only shows a link between the virus and chronic fatigue syndrome, or CFS, and does not prove that the pathogen causes the disorder.
Much more study would be necessary to show a direct link, but Mikovits says the study offers hope that CFS sufferers might gain relief from a cocktail of drugs designed to fight AIDS, cancer and inflammation.
"You can imagine a number of combination therapies that could be quite effective and could at least be used in clinical trials right away," says Mikovits.
She says AIDS drugs such as reverse transcriptase inhibitors and integrase inhibitors, as well as nonsteroidal anti-inflammatory drugs and cancer-fighting proteasome inhibitors, could be tested as potential treatments for CFS.
Biochemist Dr Stuart Le Grice of the US National Cancer Institute, who also worked on the study, says some AIDS drugs may be ineffective against XMRV because many are tailor-made for HIV.
"But we've learned a lot from HIV, and if XMRV does become a serious issue, we can bring that to bear very quickly," says La Grice.
According to the US Centers for Disease Control and Prevention, CFS impairs the immune system and causes incapacitating fatigue. Sufferers can also experience memory loss, problems with concentration, joint and muscle pain, headaches, tender lymph nodes and sore throats.
Symptoms last at least six months and can be as disabling as multiple sclerosis or rheumatoid arthritis, the CDC says.
But Mikovits says there is currently no treatment for CFS aside from cognitive behavioural therapy to help patients cope with the disorder's crippling effects.
Cause and effect
The XMRV virus is a retrovirus, like the HIV virus that causes AIDS. As with all viruses, a retrovirus copies its genetic code into its host, but uses RNA instead of using DNA to do so.
Known formally as xenotropic murine leukemia virus-related virus, XMRV has also been found in some prostate tumours and is also known to cause leukaemia and tumours in animals.
Mikovits' team says further research must now determine whether XMRV directly causes CFS, is just a passenger virus in the suppressed immune systems of sufferers or a pathogen that acts in concert with other viruses that have been implicated in the disorder by previous research.
"Conceivably these viruses could be co-factors in pathogenesis, as is the case for HIV-mediated disease, where co-infecting pathogens play an important role," the report's authors write.
Because 3.7% of the healthy test population tested positive for XMRV, the researchers estimate several million otherwise healthy people in the United States could be infected with it.