5. Variant CJD

Abstract

The primary epidemic of variant Creutzfeldt- Jakob disease (vCJD) may be nearly over. There have been no deaths from vCJD in the UK since 2013 and none worldwide since 2014. The mismatch between the observed number of cases and the estimated levels of oral exposure of human populations to BSE prions, particularly in the UK, is unexplained, but most likely relates to a significant species barrier between bovines and humans. There have been 4 cases of vCJD born after 1989 in continental Europe but none born after this date in the UK, suggesting that the measures introduced in the UK in 1989 to reduce human exposure to the BSE agent may have been effective, despite not being fully enforced. There have been 4 instances of secondary transmission of vCJD through blood transfusion identified to date in the ongoing UK TMER study, but none reported since 2007. Detailed analysis of transfusion history in vCJD cases indicates that only a small number of such cases, if any, could have been missed by epidemiological surveillance. Transfusion transmission is a relatively efficient route of infection: there has been transmission of infection in 4/33 recipients who survived 5 y or more following transfusion from a donor who later developed vCJD, and laboratory transmission studies do not indicate an adaption of the agent after secondary transmission. These observations are difficult to reconcile with prevalence studies in the UK which have led to estimates that 1/2000 of the general population may be infected with vCJD. It is possible that measures introduced to minimise the risk of transfusion transmission, including leucodepletion of blood components, may have contributed to the limited number of transfusion transmitted cases observed. There is, to date, no evidence of secondary transmission of vCJD via contaminated surgical instruments, via organ or tissue transplant or vertically from mother to child, but the period of observation is too short to exclude the possibility that cases linked to these potential routes of transmission may be observed in the future. There are also concerns about further outbreaks of vCJD occurring in individuals with different genetic backgrounds, but this has not been observed to date, and it is now 22 y since the clinical onset in the first case of vCJD identified in the UK.