The link between the new variant CJD and BSE

Variant Creutzfeldt-Jakob disease (vCJD) is a novel human prion disease caused by the bovine spongiform encephalopathy agent

• most cases have occurred in the UK, with smaller numbers in 11 other countries
• all definite vCJD cases have occurred in methionine homozygotes at codon 129 in the prion protein gene
• following oral infection, the vCJD agent appears to replicate in lymphoid tissues during the asymptomatic phase of the incubation period

Experiments in mammals have shown that it is possible to transmit prion diseases within and between species, and evidence such as kuru clearly demonstrates that humans may acquire prions by eating contaminated material. Results of experiments however does suggest the existence of a species barrier, whereby it is relatively difficult to transmit prions across species, for instance sheep have had scrapie for 200 years with no discernible ill affects on man.

Molecular analysis of prion proteins and particularly their strain variation has shown that prions found in patients suffering from the new variant CJD have strain properties distinct from other types of CJD, and resemble prions found in mice, cats and macaques that have been infected with Bovine Spongiform Encephalopathy (BSE) material.

Variant CJD resulting from the human transmission of BSE mainly through dietary exposure, has steadily declined in incidence in the UK since 2000, with a total 176 cases (1)

• the prevalence of subclinical infection indicated by anonymous surveys of appendiceal tissue, remains a significant concern at around 1:2000 in the UK (http://www.hpa.org.uk/hpr/archives/2012/news3212.htm#bnrmlprn)
  • subclinically infected individuals may never convert to clinical cases, however they pose risks for iatrogenic transmission by blood or blood product transfusion, by dentistry and surgery.

Reference:

• Ironside J.W. Variant Creutzfeldt-Jakob disease: an update. Folia Neuropathol. 2012;50:50-56