Seroprevalence of xenotropic murine leukemia virus-related virus in normal and retrovirus-infected blood donors.
Qiu, Xiaoxing, Swanson, Priscilla, Tang, Ning et al. · Transfusion · 2012 · DOI
Quick Summary
Researchers tested blood samples from over 2,000 donors worldwide to see if they carried XMRV, a virus that had been suggested as a possible cause of ME/CFS. They found very little evidence that XMRV was present in most people's blood. The small amount of positive results they found were likely false positives caused by confusion with a different virus (HTLV-I) that shares similar genetic sequences.
Why It Matters
Early case reports associated XMRV with ME/CFS, raising major concerns about disease transmission through blood transfusion and possible viral etiology. This large, multi-population study provided important negative evidence that helped resolve controversy around XMRV prevalence in blood supplies and informed the broader scientific reassessment of XMRV's role in ME/CFS.
Observed Findings
Overall XMRV seroreactivity was 0-0.6% in normal and most retrovirus-infected donors, with the exception of HTLV-I-infected donors showing 4.9% seroreactivity.
All seroreactive samples showed antibodies to only a single XMRV protein (either p15E or gp70), never multiple proteins.
No seroreactive samples had detectable XMRV pol or env sequences by real-time reverse transcriptase PCR.
HTLV-I-infected donors had elevated p15E seroreactivity (4.1%) compared to other groups.
HTLV-I and XMRV transmembrane proteins showed high sequence conservation in their immunodominant regions, explaining cross-reactivity.
Inferred Conclusions
XMRV is not prevalent in normal or most retrovirus-infected blood donors, supporting transfusion safety.
Detected seroreactivity in HTLV-I-infected donors represents cross-reactive antibodies rather than true XMRV infection.
The absence of complete serological profiles (single protein only) and lack of viral sequences argue against productive XMRV infection in blood donors.
Earlier reports associating XMRV with disease may have involved assay cross-reactivity artifacts.
Remaining Questions
Is XMRV prevalence different in ME/CFS patient populations compared to healthy blood donors?
What This Study Does Not Prove
This study does not prove XMRV never causes ME/CFS or that it is not present in some ME/CFS patients specifically—it only shows low prevalence in blood donor populations. The study cannot establish whether seroreactivity patterns differ in ME/CFS populations versus healthy donors. Cross-sectional design limits ability to determine causal relationships.
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 →