A new study has found that a virus called xenotropic murine leukemia virus (XMRC) may be linked to chronic fatigue syndrome (CFS). The XMRC is part of a family of viruses known as murine leukemia viruses (MLV). The MLV is a type of retrovirus and it causes cancer in mice. The new study was published in the Proceedings of the National Academy of Sciences and its findings conflict with some earlier studies, which had claimed that XMRV or other viruses in this family are not found in the blood of people with CFS.