‘High prevalence’ of vCJD proteins
Tuesday 15th October 2013, 4:11PM BST.
One in 2,000 people in the UK carries abnormal proteins linked to variant Creutzfeldt-Jakob disease (vCJD) – the human form of mad cow disease, new research has shown.
Experts said their study has “important implications” for how blood and blood donations are managed and for the handling of surgical instruments.
The findings suggest a “high prevalence of infection with abnormal prion protein, indicating vCJD carrier status in the population”.
But the researchers noted that, despite the higher number of carriers, just 177 vCJD cases have been reported to date in the UK.
vCJD is a fatal, degenerative brain disorder which is the human form of Bovine Spongiform Encephalopathy (BSE).
The disease is believed to have passed from cattle to humans through consumption of meat products contaminated with BSE.
Large numbers of the UK population were exposed to BSE prions in the late 1980s and early 1990s.
The new study, published online in the British Medical Journal (BMJ), involved analysis of more than 32,000 appendix samples from people of all ages who had their appendix removed between 2000 and 2012 at over 41 hospitals in England.
Of these samples, 16 tested positive for abnormal prion protein, indicating that one in 2,000 of all people are likely to be carriers.
The researchers, including a team from Public Health England, found that prion protein in those born between 1941 and 1960 did not differ significantly from those born between 1961 and 1985.
Presence of the protein was also similar in both men and women.
The researchers expressed concern that some of the 16 samples produced information which might suggest people may be susceptible to developing the condition over a longer time than previously thought, or may not show any signs of disease at all.
But they said the number of patients diagnosed with vCJD is still well below the number suggested by the prevalence of abnormal proteins.
Professor Noel Gill, lead investigator at Public Health England, said: “Prevalence studies such as this are important as they enable us to interpret the impact of the BSE epidemic on the population of Britain and strengthen the basis for ongoing risk assessments.
“There are already extensive measures in place to prevent the potential spread of infection.
“Prion diseases can have very long incubation periods, and an understanding of prevalence can help researchers devise measures to prevent further transmission of the disease.
“It is not known whether all infected individuals will develop disease. The peak of the vCJD epidemic in the UK was in 2000, where 27 probable or definite cases were diagnosed that year. Only one case of vCJD has been diagnosed in 2013 in the UK.”
He said further research on samples from the 1970s and earlier – before BSE appeared – were now underway to see whether prion proteins also occurred then, which could reduce the significance of the new findings.
Dr Graham Jackson, from the Medical Research Council Prion Unit at University College London’s Institute of Neurology, said: “Whilst the study is much needed and offers both confirmation and refinement of previous studies, further work is still required.
“Given the high levels of infection indicated by this research It is now crucial we establish how many people in the UK harbour that infection in their bloodstream in order to adequately assess the risks of transmission through contaminated blood donations.
“Studies to develop new blood tests for CJD must remain a priority to assist with screening and protecting the UK blood supply.”
Professor Azra Ghani, a reader in infectious disease modelling at Imperial College London, said: ” The results from this large-scale survey are important in confirming the presence of a higher prevalence of abnormal prion protein compared with the 177 confirmed cases of vCJD.
“Whilst the lack of new cases remains reassuring, these results highlight the need to maintain both case surveillance and precautionary measures to prevent onward transmission, over the coming decade.”
Professor Gill said the findings did not indicate that twice as many people are carrying vCJD as previously thought.
Earlier studies have suggested around one in 4,000 people carry vCJD proteins.
“The range of uncertainty overlaps with previous studies,” he said. “Ours is a more robust figure.
“This new survey is a larger survey so we have more confidence in the result.
“In the earlier survey, it was smaller and they only had three positive samples, we have 16.
“The phenomenon is more real in our study. It is a more robust estimate.
“Technically, the estimate is the same as the previous study.”