Study Examines Prevalence of Abnormal Prion Protein Linked to vCJD

Public Health England researchers have reported that the abnormal prion protein (PrP) linked to variant Creutzfeldt-Jakob Disease (vCJD) the human form of bovine spongiform encephalopathy (BSE)—is potentially more prevalent than previously thought, raising concerns about the cross-contamination risks associated with blood, blood products and surgical instruments. Noel Gill, et al., “Prevalent abnormal prion protein in human appendixes after bovine spongiform encephalopathy epizootic: large scale survey,” British Medical Journal, October 2013. After finding that 16 out of 32,411 appendix samples obtained between 2000 and 2012 tested positive for abnormal PrP, the study’s authors estimated an overall prevalence of 493 per million population, nearly double the 237 per million point estimate measured in an earlier survey of appendixes. “Unlike in clinical cases of variant CJD, no particular age group or geographic region was affected, and no susceptible genotype was identified,” according to a concurrent BMJ editorial.

The researchers noted, however, the growing discrepancy between “the prevalence of vCJD prions observed in the exposed population and the relatively small number of patients who have developed vCJD.” In particular, they suggested that “the human transmission barrier for [BSE] may be high for clinical disease but substantially lower for peripheral lymphoreticular infection,” adding that infection of the central nervous system with vCJD prions “may greatly favor the methionine homozygous genotype, peripheral lymphoreticular infection may be much less selective, or even favor the valine homozygous genotype.” To help answer these questions, the study recommends the development of a human blood screening test for abnormal PrP in addition to a survey of appendixes removed before the BSE outbreak started in the mid to late 1970s.

“It is important to note the presence of the abnormal protein in the appendix does not confirm an individual will develop vCJD,” explained Bath University Professor David Brown, a former government advisor on BSE, in an October 15, 2013, Independent article. “As the authors themselves point out, the incidence of vCJD is very small in relation to those who were exposed to BSE. Therefore this result does not indicate one in 2,000 people carry vCJD, and it could just be down to people who carry the abnormal protein in their appendix … At most the report suggests a broad range of people could be carriers of a prion disease, which was suspected anyway.”