"Chronic fatigue syndrome has long been a medical mystery and the subject of debate, sometimes bitter, among doctors, researchers and patients. It affects at least one million Americans, causing extreme fatigue, muscle and joint pain, sleep problems, difficulty concentrating and other symptoms. The new suspect is a xenotropic murine leukemia virus-related virus, or XMRV, which probably descended from a group of viruses that cause cancer in mice.
To determine whether XMRV is to blame, more studies are needed, said Dr. John Coffin, a professor of molecular biology and microbiology at Tufts University. It would help to find an animal model, he said, and to look at stored blood samples to find out if there were people who became ill some set amount of time after contracting the virus. If antiviral drugs make patients improve, that will also help make the case against the virus, he said."