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Home › Topics › Infectious Diseases › Infections A-Z › Creutzfeldt-Jakob Disease (CJD) › Abnormal prion protein prevalence studies ›Background
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Background

Variant Creutzfeldt-Jakob disease (vCJD) is a Transmissible Spongiform Encephalopathy (TSE) first identified in the United Kingdom (UK) in 1996. Scientific data indicate that vCJD is the manifestation in humans of infection with the agent that causes Bovine Spongiform Encephalopathy (BSE) in cattle. It is probable that the majority of the UK population have been exposed to the BSE agent through their diet. Unfortunately, predicting the likely number of vCJD cases with sufficient confidence is difficult because the mean incubation period is likely to be more than ten years and there is considerable uncertainty about the pathogenicity of the BSE agent in humans. Whilst the number of cases so far identified has been small (174 cases in the UK at the end of 2010), it is conceivable that a relatively large number of people are infected. One particular public health concern is that infected individuals might pass the infection to others through surgical instruments, blood donation, or tissue and organ donations. This may lead to a self-sustaining secondary epidemic of vCJD in the population. Rational planning of interventions to limit the impact of the vCJD epidemic and of care provision for those who will develop the disease would be greatly improved if robust estimates of the prevalence of vCJD infection in the population could be derived.

One source of evidence for the current estimate of the prevalence of subclinical infection is the earlier study of appendix and tonsil tissue carried out in 20041. This survey found three positive samples out of 12,674 tested for PrPCJD using immunohistochemistry. The prevalence estimate calculated from this study was 235 per million (95% Confidence Interval (CI): 49-692 per million) – or 380 per million (95% CI=80-1120 per million) in the 1961 to 1985 birth cohort, since all the positives where in this cohort.

In April 2008, the Spongiform Encephalopathy Advisory Committee (SEAC) considered available data from the National Anonymous Tonsil Archive (NATA)2. At that time no PrPCJD positive samples had been found from analysis of nearly 55,000 samples, including about 11,000 samples from the 1961 to 1985 birth cohort3. Statistical analysis of the data from the earlier study and NATA showed that, because of the wide confidence intervals around both prevalence estimates, the data sets were statistically consistent with each other. However, should the lack of PrPCJD positive samples from NATA continue as more samples are collected and analysed, the two data sets will at some stage become discrepant.

In the face of continued uncertainty over possible discrepant results between both prevalence surveys, together with the urgency to resolve this uncertainty, SEAC advised that, provided appendix samples were collected from the appropriate birth cohort, (1941 to 1960 and 1961 to 1985) and these samples were tested using the same immunohistochemistry technique as used in the previous appendix and tonsil tissue study, the data from a new appendix study could be combined with the previous study. This would allow further refinement of the current estimates for the prevalence of subclinical infections.

1.       Hilton DA, Ghani AC, Conyers L, Edwards P, McCardle L, Ritchie D, et al. Prevalence of lymphoreticular prion protein accumulation in UK tissue samples. J Pathol 2004; 203: 733-9.
2.       Spongiform Encephalopathy Advisory Committee (SEAC). Prevalence of subclinical variant Creutzfeldt-Jakob Disease infections. August 2008. SEAC position statement.
3.       Clewley J, Kelly CM, Andrews N, Vogliqi K, Mallinson G, Kaisar M, et al. Prevalence of disease related prion protein in anonymous tonsil specimens in Britain: cross sectional opportunistic survey. BMJ 2009: 338: b1442.