Bovine encephalopathy

Mr Neville Steven Percy spbcnsp at ucl.ac.uk
Mon Apr 18 08:08:04 EST 1994


leach at mbcrr.harvard.edu (Martin Leach) writes:
>In article <766323432snz at chatham.demon.co.uk>, ohgs at chatham.demon.co.uk
>(Oliver Sparrow) wrote:

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>> It has become an orthodoxy that BST is the consequence of an 
>> infectious agent which is somehow passed through the food chain, notably 
>> when ruminants eat food made from the bodies of animals which were themselves
>> infected with BSE.

>If i believe correctly - scrapie is prevalent in old sheep (approx 40%).
>Scapie which is in fact prion is the causitive agent. I have heard various
>stories regarding how BSE suddenly exploded in england. It all starts off
>with the chernobyl explosion. After the explosion radioactive dust etc..
>drifted across europe and some landed over england, especially over the
>sheep-farming areas. When tested these sheep contained unacceptable levels
>of radioactivity to allow them for human consumption - as the british
>public consume relatively large amounts of lamb meat. Instead of
>slaughtering most of the sheep they were allowed to grow old and a very
>large population of old sheep now inhabited UK. As 40% of old sheep usally
>get scrapie anyhow, this now meant that there was a larger number of
>scrapie infected sheep. Also around this time the extraction procedure for
>making bonemeal (cow-feed supplement) was changed (according to Stan
>Pruisner). The result being that scrapie infected material was rife in the
>bonemeal feed, and given to cattle. The scrapie manifested as BSE in the
>cows.

I am currently on the 3rd year of a PhD in the prion field, but I've never
heard anything connecting it with Chernobyl !!!!  I suppose Martin Leach does
make it fit logically into the picture, though...
The controversy over the outbreak of BSE now seems to have all been settled,
and it is indeed down to the change in the process for bonemeal handling.
In a large part, this was a consequence of an international slump in the tallow 
market: the tallow obtained by using solvents to extract the fats from the
sheeps carcasses was suddenly not worth as much; the solvent-extraction was 
suddenly costing more, and it was replaced with simple steam-treatment.

No one expected anything like the transmission of Scrapie to cows, Prion 
diseases had never previously crossed the species barrier...   but it has to be
said: no other country felt such an immediate need to cut costs as Thatcher's 
Britain... :{  

The incidence of BSE is now (finally) tailing off due to much more rigorous 
feed policies, but there is a lingering 'possibility' (I'm not sure what to 
say here... they MADE me sign it!) that vertical transmission from cow to 
calf might occur, so the disease might be very hard to totally eradicate.



>> I am aware of no systematic technique by which BSE can be deliberately 
>> transmitted from an infected animal to another. 

>To test transmissibility of BSE infected material experiments performed
>include:
>intraocular injections of brain homogenate into eg. marmosets. This has
>been performed by Ridley and Baker (i used to work in the same dept.
>Psychiatry at th CRC in harrow for the MRC).
>I have even seen a fax of a paper showing that BSE was transmitted to mice
>by feeding them brain homogenate.

To date, the only assay for infectivity is a bio-assay using brain homogenates
inoculated intracerebrally.  The recipient mice die of experimental Scrapie
at ~200 days.


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>> Might we, therefore, be seeing a disorder which has a genetic aetiology
>> rather than something caused by a mysterious infectious agent...

>I am not sure if a mutation in the prion gene has been found in cattle or
>sheep.

Everyone has been looking, especially given the parallels with Creutzfeldt-
Jakob Disease (CJD), and the rarer diseases Gerstmann Straussler Scheinker
Syndrome and Fatal Familial Insomnia, which give incontrovertible evidence
of a genetic disease with basically BSE/Scrapie pathology.  No mutation has 
ever been found in the prion-protein gene which bears the mutations in CJD,
GSS and FFI.


Heh, I could write this stuff all day...  but we're probably boring most people
already!  I only get this computer access for work; it's great to be actually 
using it for something work-related!  (:>

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                                                   Nev Percy ; spbcnsp at ucl.ac.uk                



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