The risk of accidental transmission of transmissible spongiform encephalopathy: identification of emerging issues.

The transmissible spongiform encephalopathies (TSEs), thought to be caused by prions, are fatal neurodegenerative disorders of humans and animals. Despite their rarity, human prion diseases have received prominence because the consumption of prion-contaminated meat from cattle with bovine spongiform encephalopathy (BSE) is thought to be responsible for the emergence of variant Creutzfeldt-Jakob disease (vCJD) in humans. Clinical criteria for the diagnosis of vCJD is now available. Recent, more startling evidence suggests that the clinical presentation of vCJD may vary and that patients may present as classical (sporadic) CJD or may have subclinical infection and be apparently healthy. These patients may still pose a risk of iatrogenic transmission through surgical or medical (blood transfusion) procedures. The aim of future work is to develop preclinical screening tests for the identification of infected but still healthy individuals. The future course of vCJD is still uncertain. Modelling studies to predict the cases of vCJD depend on the date of origin of BSE and time of infection, which is, at best, only approximated. As the number of cases of BSE in the UK declines, the risk of BSE in other countries from imported cattle or meat and bone meal from the UK has been increasing. It is also recognized that other animal species (farmed, domestic and wild animals) other than cows are susceptible to TSEs. The possibility of interspecies transmission of TSEs and the global presence of the disease suggests a need for a co-ordinated worldwide risk management approach to eradicate TSEs.