Khan, A S, Heneine, W M, Chapman, L E et al. · Annals of internal medicine · 1993 · DOI
Researchers tested whether a virus called HTLV-II might be a cause of ME/CFS by comparing blood samples from 21 people with CFS to 21 healthy controls. They found no trace of the HTLV-II virus in any of the participants, and found no differences between the two groups in exposure to activities that spread viruses. This study argues against the idea that HTLV-II is linked to ME/CFS.
In the early 1990s, many hypotheses about ME/CFS etiology were proposed, including retroviral infection. This study helped rule out HTLV-II as a primary factor, narrowing the field of investigation and preventing resources from being spent on less promising leads. Clarifying what does not cause ME/CFS is important for redirecting research toward more plausible mechanisms.
This study does not prove that no retrovirus plays any role in ME/CFS—it specifically rules out HTLV-II and common retroviral transmission routes in this small population. It does not exclude other viruses (such as EBV, HHV-6, or enteroviruses) that were investigated in later research. The small sample size limits generalizability and the study's statistical power to detect rare associations.
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
Khan, A S, Heneine, W M, Chapman, L E, Gary, H E, Woods, T C, Folks, T M, et al. (1993). Assessment of a retrovirus sequence and other possible risk factors for the chronic fatigue syndrome in adults.. Annals of internal medicine. https://doi.org/10.7326/0003-4819-118-4-199302150-00001
BibTeX
@article{mecfsatlas-khan-1993-assessment-retrovirus,
author = {Khan, A S and Heneine, W M and Chapman, L E and Gary, H E and Woods, T C and Folks, T M and Schonberger, L B},
title = {Assessment of a retrovirus sequence and other possible risk factors for the chronic fatigue syndrome in adults.},
journal = {Annals of internal medicine},
year = {1993},
doi = {10.7326/0003-4819-118-4-199302150-00001},
note = {PubMed: 8420441},
url = {https://www.mecfsatlas.com/evidence/khan-1993-assessment-retrovirus},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-27. https://www.mecfsatlas.com/evidence/khan-1993-assessment-retrovirus
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