15 October 2013

Carriers of mad cow disease double previous estimate

by Will Parker

Analyzing thousands of tissue samples from surgical procedures carried out around the United Kingdom (UK), researchers have estimated that the number of people carrying variant Creutzfeldt-Jakob prions to be double previous estimates. Reported in the British Medical Journal, the survey is likely the most robust prevalence measure to date across a wide range of age groups.

Variant Creutzfeldt-Jakob disease (vCJD) is a degenerative brain disease - often called the human form of bovine spongiform encephalopathy (BSE or "mad cow disease"). It was first identified after widespread human exposure to BSE prions in the late 1980s through contaminated meat products. Previously, studies had estimated that around one in 4,000 people may be carrying the vCJD prions.

In the new study, a team of UK researchers examined more than 32,000 appendix samples from people of all ages who had their appendix removed between 2000 and 2012. Of these, 16 samples were positive for the abnormal prion protein, indicating an overall prevalence of 493 per million people. From this figure, the research team estimates that one in 2,000 people are likely to be carriers.

Interestingly, the presence of the prion protein in those born in 1941-60 did not differ significantly from those born between 1961 and 1985 and was similar in both sexes. Additionally, there were no apparent geographic factors contributing to prevalence.

Despite the large increase in the estimate of carriers of the prion, the researchers stress that the number of patients with clinical vCJD is still well below the number suggested by the prevalence of the abnormal prion protein. "Although the disease remains rare, infection may be relatively common," they note.

They admit, however, that much uncertainty remains about how many of these carriers will eventually develop the disease and it is unclear what risk carriers pose of transmitting the disease by blood transfusion or surgery. The researchers say they now want to examine tissue from the 1970s and earlier, before BSE appeared.

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Source: British Medical Journal