PCR master mixes harbour murine DNA sequences. Caveat emptor!
Tuke, Philip W, Tettmar, Kate I, Tamuri, Asif et al. · PloS one · 2011 · DOI
Quick Summary
This study found that the laboratory chemicals used to detect viruses in blood samples may themselves contain mouse virus DNA, which can contaminate test results. When researchers tested water samples (with no actual virus present) using common laboratory kits, they still found mouse virus sequences—the same sequences that had been previously reported in ME/CFS patients. This suggests that previous findings of these viruses in ME/CFS patients may have been false positives caused by contaminated testing materials rather than actual infections.
Why It Matters
This study is critical because it identifies a major technical artifact that may invalidate previous claims of viral causation in ME/CFS. Understanding the source of false-positive results is essential for properly evaluating biomarker research and preventing misguidance of clinical investigations and patient expectations. Rigorous quality control in viral detection methodologies is fundamental to establishing genuine disease associations.
Observed Findings
PCR amplification of water-only negative controls using Invitrogen Platinum Taq generated 4 gag sequences with mouse-derived DNA contamination
Applied Biosystems Taq Gold LD re-amplification of an Invitrogen product generated an additional contaminating sequence
Sequences from PCR master mix contamination showed remarkable homology to endogenous murine MLVs and previously published pMLV sequences from CFS patients
Two blood donor samples that initially tested positive by gag PCR had tested negative using two alternative PCR-based techniques
Commercial PCR reagents contained murine DNA at levels where contamination was not immediately apparent
Inferred Conclusions
PCR master mixes can be a source of murine DNA contamination in viral detection assays
Previous reports of pMLV in CFS patients likely resulted from reagent contamination rather than true viral infection
Viral detection methodologies homologous to endogenous sequences require exceptional caution regarding reagent quality and contamination control
The apparent high prevalence of pMLV in CFS (86.5%) can be substantially explained by systematic contamination in the detection process
Remaining Questions
Can alternative viral detection methods (e.g., deep sequencing with contamination controls, infectious clone assays) definitively establish presence or absence of these viruses in ME/CFS?
What This Study Does Not Prove
This study does not prove that XMRV or pMLV are definitively absent from ME/CFS patients, nor does it establish that no retroviral involvement exists in the disease. It demonstrates a technical problem with one detection method but does not rule out the possibility that other, better-controlled studies might find genuine viral associations. The findings apply specifically to PCR-based detection using contaminated commercial reagents and may not generalize to all virology research methodologies.
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 →
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