A study led by Sebastian Brandner at the Department of Neurodegenerative disease, UCL Institute of Neurology, in collaboration with the AHVLA in Weybridge and Public Health England shows all ages and genotypes to be affected.

The survey, published in this week's BMJ, provides the most robust prevalence measure to date - and identifies abnormal prion protein across a wider age group than found previously and in all genotypes, indicating “infection” may be relatively common and doctors need to understand the public health measures that are in place to protect patients.

Variant Creutzfeldt-Jakob disease (vCJD) is a degenerative brain disease which emerged after widespread exposure to BSE prions in the late 1980s and early 1990s through contaminated meat products in the food chain. 177 clinical cases of vCJD have been diagnosed to date in the UK.

In the present study, over 32,000 anonymous appendix samples were examined from people of all ages who had their appendix removed between 2000 and 2012 at over 41 hospitals across England. Of these, 16 samples were positive for abnormal prion protein, indicating an overall prevalence of 493 per million population, or one in 2,000 people are likely to be carriers. No difference was seen in different birth cohorts (1941-60 and 1961-85), in both sexes, and there were no apparent difference in abnormal prion prevalence in three broad geographical areas.

Genetic testing of the 16 positive samples revealed a higher proportion of valine homozygous (VV) genotype on the codon 129 of the gene encoding the prion protein (PRNP) compared with the general UK population. This also differs from the 177 patients with vCJD, all of whom to date have been methionine homozygous (MM) genotype.

Sebastian Brandner commented "It is a concern is that individuals with this VV genotype may be susceptible to developing the condition over longer incubation periods, or they may not show any clinical signs of disease.

An important finding is that the number of patients with clinical vCJD is still well below the number suggested by the prevalence of abnormal prion protein, even for those who carry the MM genotype. Nevertheless, it is essential to continue research into tests to detect abnormal prion protein in blood – and to examine tissue from the 1970s and earlier, before BSE appeared".

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Gill, O.N. et al. Prevalent abnormal prion protein in human appendixes after bovine spongiform encephalopathy epizootic: large scale survey BMJ 2013; 347 doi: 10.1136/bmj.f5675 (Available online 15 October 2013)

Salmon, R. How widespread is variant Creutzfeldt-Jakob disease? (Editorial)  BMJ 2013; 347 doi: 10.1136/bmj.f5994 (Available online 15 October 2013)