Knox, Konstance, Carrigan, Donald, Simmons, Graham et al. · Science (New York, N.Y.) · 2011 · DOI
This study tested blood samples from 61 ME/CFS patients to look for viruses called XMRV and related mouse viruses that had been reported in earlier research. The researchers found no evidence of these viruses in the patients' blood, even in 43 patients who had previously tested positive. They concluded that earlier findings were likely due to contamination in the laboratory rather than actual infection.
This study is important because it addresses a major claim linking a retrovirus to ME/CFS that had generated significant hope and research effort. By demonstrating that previous positive results were likely laboratory artifacts, it refocused the field on other research directions and emphasized the importance of rigorous contamination controls in ME/CFS virology studies.
This study does not prove that no infectious agent is involved in ME/CFS—it only addresses these specific gammaretroviruses. It does not establish what causes ME/CFS or rule out other potential viral or microbial factors. The findings also cannot determine why some patients initially appeared to test positive, though contamination is the most likely explanation.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Knox, Konstance, Carrigan, Donald, Simmons, Graham, Teque, Fernando, Zhou, Yanchen, Hackett, John, et al. (2011). No evidence of murine-like gammaretroviruses in CFS patients previously identified as XMRV-infected.. Science (New York, N.Y.). https://doi.org/10.1126/science.1204963
BibTeX
@article{mecfsatlas-knox-2011-evidence-murine,
author = {Knox, Konstance and Carrigan, Donald and Simmons, Graham and Teque, Fernando and Zhou, Yanchen and Hackett, John and Qiu, Xiaoxing and Luk, Ka-Cheung and Schochetman, Gerald and Knox, Allyn and Kogelnik, Andreas M and Levy, Jay A},
title = {No evidence of murine-like gammaretroviruses in CFS patients previously identified as XMRV-infected.},
journal = {Science (New York, N.Y.)},
year = {2011},
doi = {10.1126/science.1204963},
note = {PubMed: 21628393},
url = {https://www.mecfsatlas.com/evidence/knox-2011-evidence-murine},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-29. https://www.mecfsatlas.com/evidence/knox-2011-evidence-murine
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