Transmissible spongiform encephalopathies: vaccine issues.

The recent emergence of bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob Disease (vCJD) suggests that transmissible spongiform encephalopathies (TSEs) pose an ongoing threat to human and animal health. To avoid iatrogenic transmission of TSEs in vaccines, strategies must be developed to obviate TSE agent infectivity in cellular substrates, cell culture media components and enzymes, and excipients, and to validate the safety of these components and field vaccines efficiently