Twice as many Britons as previously thought could be carrying the human form of "mad cow" disease, variant CJD.
Researchers believe one in 2,000 people in the UK is a carrier of the disease linked to eating contaminated beef.
Their estimate in the BMJ comes from studying more than 32,000 samples of human tissue removed during appendix operations carried out between 2000 and 2012 at 41 hospitals.
It remains unclear if any of these carriers will ever develop symptoms.
Early predictions of a vCJD epidemic didn't come to fruition.
To date, here have been 177 UK deaths from vCJD. Most of these occurred in the late 90s and early 2000s. There has been only one death in the last two years.
The rare, fatal disease progressively attacks the brain.