Risk assessment: xenotropic murine leukemia virus-related virus (XMRV) and its implications for blood donation

Following a request from the European Commission, ECDC produced in July 2011 a risk assessment to assess the possible implications of XMRV on blood donation. A review of the published literature at the time showed that there is not enough evidence to reliably assess the potential role of the virus in human pathology. Currently, the scientific data are incomplete and conflicting. It seems likely that the findings in two studies on XMRV and murine leukemia virus in CFS patients were potentially due to laboratory contamination, and the majority of the evidence favours the conclusion that there is no causal relation between XMRV and CFS. With the development of validated assays, additional data will become available in the near future which will help inform decisions on blood donor eligibility and screening. Background: XMRV is a member of the Gammaretrovirus genus of the Orthoretrovirinae subfamily of Retroviridae with high sequence similarity to endogenous murine leukemia viruses. It is believed to have originated in mice and is the first agent of its class to be identified in humans; it likely evolved as a result of a recombination event between polytropic and xenotropic MLV. Similar agents are found in a wide range of mammalian species and include the porcine endogenous retrovirus, the feline leukaemia virus, the koala retrovirus and the gibbon ape leukaemia virus, that can cause leukaemia and other syndromes in their host species. In humans, chronic fatigue syndrome (CFS) – also referred to as myalgic encephalomyelitis (ME) – is a disease of unknown aetiology but suspected to involve viral infection and characterised by debilitating fatigue and other symptoms.