Chronic fatigue syndrome, a prolonged and severe tiredness not relieved by rest, affects about 17 million people worldwide, report UTMB’s Norbert Herzog and David Niesel in this week’s installment of Medical Discovery News. Early symptoms are similar to common viral infections with muscle aches, headache and fatigue. What makes CFS debilitating is that these symptoms can last six months or more. Scientists believe a retrovirus called XMRV may be to blame because it leads to a long-term immune response. If researchers link XMRV to CFS, drugs used to treat HIV may be effective because XMRV is in the same family of viruses. MDN airs locally at 10 a.m. Saturday on KUHF.