Confirming earlier scientific doubts, a new study concludes that chronic fatigue syndrome is not caused by two viruses known as XMRV and pMLV.
Researchers from the U.S. National Institutes of Health, the U.S. Centers for Disease Control and Prevention, Columbia University and other institutions, including some scientists who did the original research, examined 147 patients with chronic fatigue syndrome from sites across the country and compared them to 146 healthy patients.
Bottom line? "This analysis reveals no evidence of either XMRV or pMLV infection," the authors wrote. The study is published in the September/October issue of the journal mBio.
Chronic fatigue syndrome, also called myalgic encephalomyelitis, affects about 1 million people in the United States, according to a Columbia news release, with women more likely to have the diagnosis. The condition is marked by unexplained fatigue that doesn't get better with bed rest.
Patients also report problems with memory or other thinking skills, muscle or joint pain, headache and other symptoms.
In 2009, a paper published in the journal Science connected the syndrome to infection with a mouse virus known as XMRV, for xenotropic murine leukemia virus-related virus.
In 2010, another study found a virus, polytropic murine leukemia virus, called pMLV, in some patients, which lent more support to a viral theory.
However, editors at Science later retracted the 2009 report, saying follow-up findings failed to confirm the original findings.
To lay the matter to rest, researchers launched the new study.
They assessed blood samples from the group affected by chronic fatigue syndrome and those not affected.
None of the samples had evidence of either virus.
The new study should end any concerns about the viruses causing the disease, said K. Kimberly McCleary, president of the CFIDS (Chronic Fatigue Immune Dysfunction Syndrome) Association of America.
"Over the past three years, more than 70 publications have followed the original report linking CFS to XMRV," she said.
The new report addresses weaknesses of past research, she said. It also "provides a conclusive answer and offers closure. The totality of published evidence indicates clearly that there should be no lingering concerns about XMRV/pMLVs infecting individuals with CFS."
"There can no longer be any ambiguity," said Dr. Jonathan Stoye, head of virology at the MRC National Institute for Medical Research, in London. "There is no remaining evidence linking XMRV or pMLV with [chronic fatigue syndrome/myalgic encephalomyelitis]," he said.
Over the years, researchers have looked at many types of infections to see if they might trigger or cause chronic fatigue syndrome, according to the CDC. Among them are the virus that causes Epstein-Barr infection, human herpes virus, the Ross River virus and others.
Studies on whether changes in a person's immune system might lead to CFS have been mixed. There is no evidence that chronic fatigue syndrome is caused by deficiencies in nutrition, although experts recommend a balanced diet for anyone with the condition.
There is no cure for chronic fatigue syndrome. According to the CDC, treatment is tailored to a person's specific symptoms. The CDC recommends addressing the most disruptive symptoms, such as fatigue, sleep problems and depression or anxiety.
