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From: TSS ()
Date: March 21, 2005 at 3:06 pm PST

-------- Original Message --------
Date: Mon, 21 Mar 2005 17:05:12 -0600
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy

##################### Bovine Spongiform Encephalopathy #####################

ARC 240/76

Research on Scrapie of Sheep

At the meeting of Council on 15 June 1976, scrapie of sheep was discussed
during consideration of the Report of the Visiting Group to the Animal Diseases
Research Association. Several important matters were raised, including the
ban recently imposed by the USDA on the use for human food not only of sheep
affected with scrapie but also of related or exposed sheep or goats. Council
decided further to discuss scrapie at its meeting on 12 October l976 with
particular reference to the question of whether the Council's Technical
Committee on Scrapie Research, which last met in 1969 and was wound up formally
when the JCO was established, should be reconstituted in order to advise on
future research policy.

The USDA concern is based on observations that the chronic progressive
degeneration of the central nervous system characteristic of scrapie has points
of similarity with certain neurological diseases of man. Although there is no
evidence that sheep meat causes these disorders in man, the fear of such a
possibility could have serious consequences for the sheep industry.

This development adds emphasis to a topic which already has a high priority in
scrapie research, viz,, the development of a test for the early diagnosis of
scrapie in the clinically healthy animal. It is at present impossible to
identify animals infected with scrapie which are in a pre-clinical state. A
number of promising approaches have been pursued, but so far without success.

Another important topic is the assessment of the hazard to man of the scrapie
agent. This depends to a large extent on gaining knowledge of the nature of the
agent, a problem which still awaits clarification in spite of a very substantial
amount of research. Although the agent is known to be transmissible, filterable,
and self-replicating, it has characteristics which are not typical of conventional
viruses. It is very resistant to heat and chemical disinfectants. Its replication
in cell culture is unusual. It provokes no immune response in the usual way,
although there are indications that new techniques are detecting a type of response.
Its nucleic acid statue is not typical of viruses and this is an aspect which has
been attracting considerable biochemical effort with the objective of isolating
scrapie—specific nucleic acid molecules.

The feasibility of breeding sheep resistant to scrapie is being investigated.
There are a number of different strains of agent, however, and there is the
problem that increased resistance to one strain might be accompanied by increased
susceptibility to another.

Another approach to control of the disease is the investigating of "blocking
agents" which might successfully compete with the acrapie agent for replication

The type of advice which should be given on control measures is being discussed
by the Ministry of Agriculture, Fisheries and Food's Scrapie Working Group on
which there are two ARS scrapie research workers.

There are a number of technical problems which although not unique to scrapie,
combine to make difficulties and increase expense. Examples are the need to
maintain experimental animals during the long incubation period in accommodation
sufficiently secure to prevent cross—infection, to take precautions in the
microbiological laboratories to prevent cross-contamination, and to provide


elaborate controls for the biochemical investigations.

Another aspect is that scrapie is a disease which is not only of agricultural
importance but is also of medical and biological significence. It is the most
convenient model for this type of infection by virtue of the susceptibility
of small laboratory animals, and certain cell lines. This raises the question
of whether scrapie research should be funded by more than one body, viz MRC
as well as ARC.

Council may feel that, in view of the complex and specialised nature of the
subject and the probability of requests for substantial financial support, it
would be advantageous to have an expert group to assess current and proposed
research and to make recommendations.


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