Since 2009, XMRV has been linked to chronic fatigue syndrome (CFS), and considered a virus that has also been detected in prostate cancer patient samples. However a new study, found in the publication Retrovirlogy, makes clear that the presence of XMRV was simply a contamination in 2009, and not this virus in particular causing chronic fatigue, also known as myalgic encephalomyelitis (ME).

CFS is characterized by long-term tiredness or fatigue that affects the everyday life of patients. There is no known cure for CFS.

Greg Towers of the University College London states:

    “Our conclusion is quite simple: XMRV is not the cause of chronic fatigue syndrome. All our evidence shows that the sequences from the virus genome in cell culture have contaminated human chronic fatigue syndrome and prostate cancer samples. It is vital to understand that we are not saying chronic fatigue syndrome does not have a virus cause - we cannot answer that yet - but we know it is not this virus causing it.”

Cells or mouse DNA is the source of XMRV in chronic fatigue syndrome samples rather than direct infection by XMRV, although chronic fatigue syndrome may, in fact, be linked to another type of virus. University College London and University of Oxford Wellcome Trust Sanger Institute team’s research demonstrated that previous studies had detected sequences that resembled XMRV, but could prove this observation stemmed from contamination by a laboratory cell line or mouse DNA.

Contaminated cell line and chronic fatigue patient samples proved to be very similar, contrary to evolutionary patterns witnesses as an infectious spread of a virus infiltrates human population.

Dr Stéphane Hué, Post Doctoral Researcher at UCL summarizes:

    “When we compare viral genomes, we see signs of their history, of how far they have travelled in space or time, we would expect the samples from patients from around the world, collected at different times, to be more diverse than the samples from within a cell line in a lab, where they are grown under standard conditions. During infection and transmission in people, our immune system would push XMRV into new genetic variants. Viral infection is a battle between the virus and the host, and XMRV does not have the scars of a virus that transmits between people.”

Researchers also found that existing methods would indicate that one in fifty human cell lines examined were infected with XMRV-related viruses. Together the results demonstrate that XMRV does not cause chronic fatigue syndrome or prostate cancer in these cases.

It is critical that containment and proper methods are implemented when searching for a disease’s cause. The study’s authors suggest more rigorous methods are used to prevent contamination of cell and DNA samples and that a consistent method is used across the board when in the pursuit of identifying causes of disease such as viruses and other infected organisms that transmit ailments.

Professor Paul Kellam, Virus Genomics group leader from the Wellcome Trust Sanger Institute, founded in 1992, concludes:

    “Increasingly, we are using DNA-based methods to accelerate our understanding of the role of pathogens in disease. These will drive our understanding of infection, but we must ensure that we close the circle from identification to association and then causation. The strongest lesson is that we must fully use robust guidelines and discriminatory methods to ascribe a cause to a disease.”

“Disease-associated XMRV sequences are consistent with laboratory contamination”
Hué S, Gray ER, Gall A et al.
Retrovirology. 2010, 7:111doi:10.1186/1742-4690-7-111

Written By Sy Kraft, B.A