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What are
TSEs?
The transmissable
Spongiform Encephalopathies are a unique set of
naturally or experimentally transmissable
neurodegenerative conditions. They are
characterised by vacuolar changes in the grey
matter of the brain and spinal cord. In addition,
there is a response from astrocytes (support cells
found in the brain), accompanied by an accumulation
of a pathological, protease-resistant form of the
naturally occurring PrP-protein. The nature of the
agent that causes the disease is still unknown, but
many believe that the faulty PrP-protein (also
called prion) is a strong candidate. But whatever
the nature of the infective agent, it is extremely
resistant to many physical and chemical agents that
are normally used to inactivate viruses.
Animal and
human TSEs
The best known
animal TSEs are mad cow disease (bovine spongiform
encephalopathy or BSE, occurring in cattle) and
scrapie (occurring in sheep and known since the
18th century). But TSE-like diseases have also been
reported in goats, mink (transmissable mink
encephalopathy, found in 1965), cats (feline
spongiform encephalopathy, FES), antilopes, deer
(chronic wasting disease) and exotic animals kept
in zoos. In humans, various
TSEs are known. They are the following: Creutzfeldt-Jakob
disease (can be caused by an infection, by a
genetic PrP mutation (approximately 10% of all
known CJD cases) or by an unknown mechanism) Gerstmann-Straussler-Scheinker
syndrome (caused by a genetic PrP mutation) Fatal Familial
Insomnia (caused by a genetic PrP mutation) Kuru (the disease
is now extinct but was caused by an infection) Variant CJD (the
'new' type of Creutzfeldt-Jakob disease, believed
to be caused by consuming products from
BSE-infected cattle) Under natural
conditions, the only TSEs that are transmissable
appear to be scrapie of sheep, chronic wasting
disease of deer and, to a limited extent, maternal
transmission of BSE. The suspicion is that new
variant CJD is associated with ingestion of food
contaminated with the agent causing bovine
spongiform encephalopathy (BSE).
In domestic cattle,
BSE is a new disease, first recorded in 1986 in the
UK. The origin of the disease is not known and it
is now thought that the occurrence of BSE
represents the amplification through the feed cycle
of a spontaneous case of spongiform encephalopathy
in cattle. The shortest incubation period reported
in experimentally infected cattle has been 3 to 3.5
years. The United Kingdom is the only country that
has reported a high incidence of the disease (1% of
all cattle at the peak of the epidemic). Other
countries with reports of BSE are Ireland,
Switzerland and, to lesser extents, Portugal,
Canada, Denmark, Italy, the Falkland Islands and
the Sultanate of Oman. In the latter countries, BSE
cases seem to be related to import of animals from
the UK. The United States is completely free from
BSE. In those countries in which cases of BSE have
been reported, strict safety measures have been
taken to prevent the further spread of the disease.
For an update of the measures taken to prevent the
spread of the disease, see ACTIP
Bulletin nr 2,
1999 and
the regulatory
and scientific update on
TSE, both
available on the ACTIP website.
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