Between 1 and 4 million Americans suffer from Chronic Fatigue Syndrome (CFS), which is a “complicated disorder characterized by extreme fatigue that may worsen with physical or mental activity, but doesn't improve with rest.” (Mayo Clinic). The cause is unknown and there is no known cure. An infectious cause has been suspected and sought for decades without success. The recent discovery of XMRV, new retrovirus found in some prostate cancer patients (but not others) prompted Lombardi and colleagues to test for its involvement with CFS. They performed PCR for XMRV gag, which encodes structural viral proteins, on peripheral blood mononuclear cells from CFS patients in a repository at their Whittemore Peterson Institute. Of 101 CFS samples tested, 68 (67%) were positive in contrast to only 8 out of 218 samples (4%) from healthy donors. Another viral gene, env, was also detected in most CFS patients positive for gag as were the proteins encoded by these genes. Oddly, patient sample WPI-1118 is negative for gag and env (Fig 1) but weakly positive by cytometry (Fig 2 A & D) and clearly positive by Western protein blot (Fig 4 A). Both B and T lymphocytes express XMRV proteins. And, for what it's worth, some CFS patient cells make virus that can productively infect other cells (shown, from Figure 3 B & C, electron micrographs of budding virus particles).
The authors note in their introduction that “patients with CFS often have active β herpesvirus infections, suggesting an underlying immune deficiency”. This increases the odds that XMRV is an opportunistic infection. The authors return to this question in their closing discussion, asking “Is XMRV infection a causal factor in the pathogenesis of CFS or a passenger virus in the immunosuppressed CFS patient population?” Stand by.
Lombardi VC, Ruscetti FW, Das Gupta J, Pfost MA, Hagen KS, Peterson DL, Ruscetti SK, Bagni RK, Petrow-Sadowski C, Gold B, Dean M, Silverman RH, Mikovits JA. "Detection of an Infectious Retrovirus, XMRV, in Blood Cells of Patients with Chronic Fatigue Syndrome". Science. 2009 Oct 8.