It's not psychological. Chronic fatigue syndrome causes severe, lasting fatigue, body aches and other symptoms and affects 17 million people worldwide, but until now, it's been a mystery ailment often attributed to a patient's psychological state. On Thursday, an article published online in Science reported that 67 percent of 101 chronic fatigue patients also had the infectious XMRV virus, or xenotropic murine leukemia virus-related virus. In contrast, 3.7 percent of 218 healthy people had the virus. According to Dr. Judy A. Mikovits, lead author of the paper, continuing research after the paper was published shows that the virus is present in almost 98 percent of 300 patients with the disease. Like HIV, XMRV is a retrovirus, and Mikovits plans to test antiretroviral AIDS drugs to see if they help chronic fatigue patients. Although more research is needed, Mikovits thinks that XMRV probably causes chronic fatigue.