Xenotropic murine leukemia virus (XMRV) is a retrovirus that is related to a group of viruses called MLVs that have been shown to cause cancer in certain mice. Retroviruses infect cells by inserting their genetic material into cells, then use the cells' own genetic processes to reproduce themselves. This infection results in either cell death or alteration of the cells' genes, causing them to become cancerous. Other retroviruses have been linked to cancers in humans.
Though current research has not proven XMRV to cause any disease in humans, the virus is getting a lot of attention lately. Some recent studies have reported a possible association between the virus and two diseases, chronic fatigue syndrome (CFS) and prostate cancer. The exact nature of this relationship is unclear, and at this time, XMRV poses no known health risk. Moreover, there are no known cases of XMRV contracted through blood transfusion. Nevertheless, several organizations, including AABB (a Lab Tests Online partner), the American Red Cross, and the US Food and Drug Administration (FDA), have taken precautionary measures to avoid collecting blood donations that may contain XMRV.
XMRV was first discovered in humans in 2006 in tissue samples from men with prostate cancer. More recently, researchers have found XMRV in blood samples from people with CFS, a debilitating disorder with no known cause, diagnostic test, or treatment. The study published in Science by Lombardi et al in October 2009 reported that viral DNA was found in 67% of 101 patients with CFS compared to less than 4% in the healthy controls. The researchers raised the concern that the virus could be transmitted via blood transfusions. However, several other studies in the US and Europe reported finding no evidence of XMRV in patients with CFS or in controls. Several just published studies have even suggested that the presence of XMRV in human samples is actually due to contamination of the testing process, explaining the difference in finding it in some studies but not others. Further studies are needed to research the possible link between CFS and XMRV. Without more definitive evidence, a cause-and-effect relationship remains unproven.
Despite the inconclusive data, several organizations have decided to err on the side of caution and have responded in an effort to help protect the US blood supply as research continues to try to better understand XMRV. The blood banking association AABB recommended last June that those with CFS should be discouraged from donating through the use of donor educational materials. The Red Cross began implementing AABB's educational materials in August. By mid-October, all regions had implemented them and earlier this month, they published a statement that the Red Cross will defer indefinitely anyone who reveals during the donor interview that he or she has been diagnosed with CFS. And just last week, the Blood Products Advisory Committee voted to recommend that the FDA require that blood collection facilities employ a screening question that asks potential donors if they have a medical history and/or diagnosis of CFS. Those who answer "yes" should be deferred from donating indefinitely, advises the FDA committee. The FDA is not required to comply with the advisory committee’s recommendations; however, the agency often does and at least gives the committee's recommendations significant consideration in its decision-making.
These measures are reasonable steps intended to help prevent XMRV from entering the blood supply. Currently there is no FDA-approved screening assay available with which to test donated blood although several companies and organizations are working to develop one. Even if one were approved, its practicality would be in question considering the lack of proof that XMRV causes harm. As AABB has stated, without evidence of transfusion transmission of these viruses and since "no causal association of XMRV with human disease has been demonstrated, a decision to introduce a blood donor screening assay, were one to become available, would appear to be premature."
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
CDC. XMRV (Xenotropic Murine Leukemia Virus-related Virus) – Questions and Answers. Available online at http://www.cdc.gov/xmrv/questions-answers.html through http://www.cdc.gov. Accessed December 2010.
Whittemore Peterson Institute. XMRV Q&A. Available online at http://www.wpinstitute.org/xmrv/xmrv_qa.html through http://www.wpinstitute.org. Accessed December 2010.
Detection of an Infectious Retrovirus, XMRV, in Blood Cells of Patients with Chronic Fatigue Syndrome. Lombardi, V C et al. Science 23 October 2009: Vol. 326 no. 5952 Pp. 585-589. Published Online 8 October 2009. Abstract available online at http://www.sciencemag.org/content/326/5952/585.abstract through http://www.sciencemag.org. Accessed December 2010.
CDC. Updates: Overview of a Peer-Reviewed Scientific Report - "Absence of Evidence of Xenotropic Murine Leukemia Virus-Related Virus Infection in Persons with Chronic Fatigue Syndrome and Healthy Controls in the United States" by William Switzer, Hongwei Jia, Oliver Hohn, et al. Retrovirology 2010, 7:57 (July 1, 2010). Available online at http://www.cdc.gov/xmrv/updates.html through http://www.cdc.gov. Accessed December 2010.
American Red Cross Statement on XMRV and Chronic Fatigue Syndrome. December 3, 2010. Available online at http://www.redcross.org/portal/site/en/menuitem.94aae335470e233f6cf911df43181aa0/?vgnextoid=dc099a02fbcac210VgnVCM10000089f0870aRCRD through http://www.redcross.org. Accessed December 2010.
AABB. BPAC Meeting - 12/14-12/15/10. Available online at http://www.aabb.org/events/government/bpac/Pages/bpacmeeting121410.aspx through http://www.aabb.org. Accessed December 2010.
AABB. Recommendation on Chronic Fatigue Syndrome and Blood Donation. Available online at http://www.aabb.org/pressroom/Pages/cfsrecommendation.aspx through http://www.aabb.org (Last Updated June 18, 2010). Accessed December 2010.
AABB. Statement Before the Blood Products Advisory Committee. Murine Leukemia Virus (MLV) Related Retroviruses and Blood Safety. Available online at http://www.aabb.org/pressroom/statements/Pages/statement121410.aspx through http://www.aabb.org. Accessed December 2010.
Contamination May Have Marred XMRV Studies. By John Gever, Senior Editor, MedPage Today. Published: December 21, 2010. Available online at http://www.medpagetoday.com/InfectiousDisease/GeneralInfectiousDisease/24006 through http://www.medpagetoday.com. Accessed December 2010.