Latest research into prevalence of vCJD consistent with findings of existing studies
22 May 2009
Latest estimates of the number of people asymptomatic for variant Creutzfeldt-Jakob disease (vCJD) in the population remain very low, according to results from a large scale study of tonsil tissue by the Health Protection Agency, published in today's BMJ (Friday 22nd May 2009).
No evidence of the abnormal prion protein associated with vCJD was found in any of the 63,000 samples analysed.
In 2004, the Health Protection Agency launched the National Anonymous Tissue Archive (NATA) to determine prevalence of asymptomatic vCJD in the population, by looking for the prion protein associated with vCJD in extracted tonsils. The tonsils are one of the sites in the body where, once infected, vCJD prions can accumulate (other sites include the spleen, appendix, lymph nodes, spinal cord and brain).
Awareness of the prevalence of vCJD in the population is important to determine the level of risk to the population and to limit the impact of infection or plan healthcare interventions for people who may develop the disease.
The survey has already involved collection and analysis of 63,000 discarded tonsils, and will continue on until a total of 100,000 samples of leftover tonsil tissue have been examined.
When the archive was established it was estimated that up to 50 of the 100,000 samples could contain the abnormal prion protein, however so far none of the samples are positive.
The findings suggest there may be fewer undetected asymptomatic cases of vCJD in the population than were previously expected. However, only by testing a larger number of tonsils and continuing and expanding on the current survey, will scientists be confident that the prevalence is lower than earlier estimates.
Dr Jonathan Clewley, an expert on vCJD at the Health Protection Agency, said: "It may be that we have seen the worst of vCJD already, although we need to keep vigilant and implement appropriate public health measures to prevent any possible secondary spread of disease.
"Estimating the prevalence of people who are carrying vCJD unknowingly is important in guiding our public health response to this disease and ensuring all necessary precautions are taken to reduce this risk of further transmission of the agent through surgical operations and other healthcare settings.
"Further studies are planned to strengthen prevalence estimates, these will involve large scale anonymous tissue surveys, and continuation with the testing of tonsil specimens especially in the older age groups."
Ends
Notes to editors
1. The National Anonymous Tissue Archive (NATA) is managed by the CJD Team at the Health Protection Agency and the Transmissible Spongiform Encephalopathies Unit for the Department of Health.
2. The findings are published in the BMJ paper; Prevalence of disease related prion protein in anonymous tonsil specimens in Britain: a cross-sectional opportunistic survey, J Clewley et al. BMJ 2009; 338: b1442.
3. 63,007 samples were taken, of which 12,763 were from the birth cohort where most cases had arisen (1961-1985), 19,908 were in the 1985-1995 cohort who would have also been exposed to BSE from infected meat or meat products. None of the samples that were investigated by immunohistochemistry or immunoblotting were positive for the presence of PrPCJD.
4. The archive is completely anonymous; after tonsils are removed, they are separated from any identifiable patient information before going into the archive. Therefore if abnormal prion proteins are found in a tonsil sample, the results cannot be passed back to the patient.
This anonymous procedure is used because the significance for an otherwise well person of finding abnormal prion protein in their tonsil tissue is unknown at present. The Research Ethics Committee that reviewed the study supported the view that the tonsils should be tested anonymously.
5. Since 1995 there have been 168 definite or probable cases of vCJD in Britain, resulting in 115 deaths from vCJD and 49 deaths thought likely to be due to vCJD. Back calculation based on these cases would suggest between 10 and 190 further clinical cases over the next ten years.
6. The NATA study is able to detect presence of the prion protein regardless of the genotype of the prion protein gene.
7. For further information on this press release please contact the Health Protection Agency's Centre for Infections press office on:
Kate Swan 020 8327 7097
Georgina Fletcher 020 8327 6690
Louise Brown 020 8327 7080
Alex Baker 020 8327 7098
David Daley 020 8327 664
Last reviewed: 21 May 2009
