When XMRV was first identified in PC patients in 2006, it did not get much public attention until a Science paper published in 2009 reported its detection in a majority (67%) of CFS patients and about 4% of healthy Americans. In this report, XMRV was shown to be infectious and could be isolated from peripheral mononuclear cells (PBMCs) and plasma, indicating that it is the first gamma retrovirus that infects humans and may be associated with human diseases. Furthermore, if confirmed, it was thought that millions of persons worldwide may harbor the new virus and thus pose a serious concern to public health and the safety of blood transfusion and organ transplantation. These findings greatly stimulated the interest of scientists in academia and government agencies to address both public health and scientific concerns about the newly identified retrovirus and its possible association with human diseases.
However, the studies that followed the original publications have yielded conflicting findings and generated more controversy than consensus about XMRV detection and its potential disease association. In 2010, Lo et al reported the detection of polytropic MLV-like sequences in 87% of CFS patients. MLV-like sequences are different from, but very similar to XMRV. The detection of polytropic MLV in CFS patients suggested that XMRV may be only one of an apparent cluster of MLV-like viruses identified in patient specimens. In this review, we describe and summarize the various testing methods and assays that have been employed for detection of XMRV and /or MLV-like virus infection in the studies that have been published until the present time.
