possibly paralysis. Nobody thought that crossing the species barrier
was possible until in 1986 in the United Kingdom a new TSE appeared:
BSE (bovine spongiform encephalopathy) or 'mad cow disease'. Epidemiological
surveys quickly showed that, via animal meal, sheep scrapie could
Ten years later the Scottish researcher Robert Will and his team
described a new variant of Creutzfeldt-Jakob disease (nvCJD) that
had been observed in the UK. They thought this form of the disease
could be due to exposure to the BSE agent. The announcement was
a bombshell. In the early 1980s an American neurologist, Stanley
Prusiner, put forward the hypothesis that TSEs are transmitted by
a single protein (earning him a Nobel prize in 1997). A new type
of infectious agent called a prion (proteinaceous infectious particle)
involves an ordinary protein of the organism known as PrP that has
undergone a change of conformation. The protein then becomes hydrophobic,
aggregates and resists the normal degradation mechanism. It thus
builds up in the brain and causes neuron destruction.
Two sets of questions
This atypical mechanism raises a number of questions that were
referred to the European Group on Research into BSE set up by the
European Commission under Charles Weissmann of Imperial College
in London, one of the leading specialists in the field of prions(1).
Two sets of questions were identified. The first concerns the practical
aspects of BSE. Has it really been transmitted to human beings?
How can we estimate the risk of transmission? Which tissues are
infected? How can diagnostic, inactivation and treatment methods
be developed? The second set of questions concerns basic research.
What is the nature of the infectious agent, how does it multiply,
what are its pathogenesis and transmission mechanisms, specificity,
susceptibility factors, etc.? The Commission launched an action
plan on these research topics with a budget of EUR 50 million.
'It is very probable that the protein is associated with the infectious
agent,' believes Dominique Dormont, a member of the Standing Committee
of the European Group on Research in BSE. 'It is probable that the
protein is itself the infectious agent, but we cannot be certain.
Nor is there any certainty about the normal function of the PrP
protein in the organism since genetically modified mice are not
affected when it is removed.
'Concrete results are now appearing in epidemiology, and Europe
has excellent diagnostic means and remarkable TSE surveillance.
A network bringing together all the European laboratories working
on prions has made it possible to establish interfaces between human
and veterinary medicine. Once the infectious agent has been finally
identified, molecular biology techniques will make it possible to
proceed very quickly. Nevertheless, not all the problems will be
resolved, and there will still be a need for further lengthy work.
A public health problem such as spongiform encephalopathies can
only be resolved by a breakthrough in basic research.'
(1) See Transmissible
Spongiform Encephalopathies: the European Initiative, Catalogue
of projects published by the 'Quality of Life and Management of
Living Resources' Programme, European Commission - EUR 19369 - ISBN