The first cases of Mad Cow disease in humans (properly called variant Creutzfeld Jakob Disease, vCJD) occurred in the late 1990s as the consequence of eating contaminated beef products. Since then, several cases of secondary infections caused by transfusions with blood from donors who subsequently developed vCJD have been reported, raising ongoing concerns about the safety of blood and blood products. A paper just published describes a new test that uses protein misfolding cyclic amplification (PMCA – like PCR for proteins) which can detect prions in blood samples from humans with vCJD and in animals at early stages of the (asymptomatic) incubation phase.
This test could be used to identify vCJD infected but asymptomatic individuals and/or for screening donated blood for the presence of the vCJD agent. In the UK, 1 out 2000 people could carry the vCJD agent. In the absence of a vCJD screen, the UK like most of the developed countries apply systematic measures aiming at mitigating the blood borne transmission risk of the disease. These measures have a substantial cost and increase the difficulty met by the blood banking system to provide certain blood products.
Preclinical Detection of Variant CJD and BSE Prions in Blood. (2014) PLoS Pathog 10(6):e1004202. doi: 10.1371/journal.ppat.1004202
The emergence of variant Creutzfeldt Jakob Disease (vCJD) is considered a likely consequence of human dietary exposure to Bovine Spongiform Encephalopathy (BSE) agent. More recently, secondary vCJD cases were identified in patients transfused with blood products prepared from apparently healthy donors who later went on to develop the disease. As there is no validated assay for detection of vCJD/BSE infected individuals the prevalence of the disease in the population remains uncertain. In that context, the risk of vCJD blood borne transmission is considered as a serious concern by health authorities. In this study, appropriate conditions and substrates for highly efficient and specific in vitro amplification of vCJD/BSE agent using Protein Misfolding Cyclic Amplification (PMCA) were first identified. This showed that whatever the origin (species) of the vCJD/BSE agent, the ovine Q171 PrP substrates provided the best amplification performances. These results indicate that the homology of PrP amino-acid sequence between the seed and the substrate is not the crucial determinant of the vCJD agent propagation in vitro. The ability of this method to detect endogenous vCJD/BSE agent in the blood was then defined. In both sheep and primate models of the disease, the assay enabled the identification of infected individuals in the early preclinical stage of the incubation period. Finally, sample panels that included buffy coat from vCJD affected patients and healthy controls were tested blind. The assay identified three out of the four tested vCJD affected patients and no false positive was observed in 141 healthy controls. The negative results observed in one of the tested vCJD cases concurs with results reported by others using a different vCJD agent blood detection assay and raises the question of the potential absence of prionemia in certain patients.