XMRV stands for "xenotropic murine leukaemia virus-related virus." Despite the fact that XMRV is not a human virus circulating in humans, it is an infectious virus. It was first identified in 2006 in samples from men with prostate cancer and later linked to chronic fatigue syndrome. This is contested as later research could not find a correlation. XMRV has also been proposed to be the cause for conditions including autism, fibromyalgia, multiple sclerosis, amyotrophic lateral sclerosis (ALS) and Parkinson’s disease.
There are only three known human retroviruses: Human T-cell leukemia virus types I and II (HTLV , the causative agent of adult T-cell leukemia); Human immunodeficiency virus types I and II (HIV, which leads to AIDS), and now XMRV -- xenotropic murine leukaemia virus-related virus.
Xenotropic refers to viruses that only replicate in cells other than those of the host species. So, XRVs are viruses that infect human cells yet are not human viruses.
Known human retroviruses infect 40–50 million people worldwide. However, there have been suggestions of unknown retroviruses in human disease, including breast cancer and primary biliary cirrhosis. Human endogenous (germline-transmitted) retroviruses have also been implicated in other cancers (these are called oncogenic human retroviruses or oncogenes) and in certain autoimmune diseases.
In 2009, researchers reported finding XMRV DNA in two thirds of 101 people with chronic fatigue syndrome (CFS) but in only 4% of healthy controls.
There is potential biohazard risk from this XMRV for humans. The fact that productively infected cells in laboratory settings have spread infection to other cell lines, raises the possibility that laboratory workers could have been unknowingly exposed to the virus.
In 2022, a diagnostic test for XMRV, known as the Simplex XMRV test, become available.
The detection of integrated XMRV proviruses in prostate cancer tissue proves it to be a genuine virus that replicates in human cells, leaving the question: how did XMRV enter the human population? There are two possible routes: either via direct virus transmission from mouse to human or via the use of mouse-related products by humans, including vaccines. We hypothesize that mouse cells or human cell lines used for vaccine production could have been contaminated with a replicating variant of the XMRV precursors encoded by the mouse genome.