Researchers have followed people who contracted Epstein-Barr virus since 1999 and looked for their symptoms and behaviors long after the virus had gone. They suspect that after a person suffers from glandular fever caused by Epstein-Barr virus, their brains suffer an injury too and keep acting as if the virus were still active in the body. Patient’s first symptoms included fever, sore throat, tiredness, and swollen lymph glands. Many of them recovered within a few weeks but some of them suffered prolonged symptoms, marked by fatigue. When the symptoms persisted for more than six months and no other possible causes were found, patients were diagnosed with chronic fatigue syndrome (CFS). When the symptoms persisted, doctors looked for the presence of virus or an abnormal immune response in the blood and nothing was found. It is suspected that certain parts of the brain, those that control perception of fatigue and pain, were damaged during the early stages on glandular fever and that it is the brain that keeps provoking the symptoms, not the virus itself. Still being just a theory, it is supported by many other scientists and more research will be done in order to prove it.