BSE questions

john brooks jbrooks at peeras.demon.co.uk
Wed Mar 27 06:40:08 EST 1996


It seems likely that pure hysteria will now take over from pure 
science in the determination of UK government policy.
Latest news suggests that 'older' cows are to be removed from the 
food chain at the end of their milking / reproductive lives.  The 
argument for this is that there are still some animals alive of 
such an age that they COULD have been exposed to BSE-contaminated 
feed and therefore MIGHT be harbouring the disease.  So we may 
conclude that a slaughter-and-incinerate policy will apply 
to roughly 15000 animals a week which would otherwise have become 
cheaper cuts of meat, sausages, etc., with a value of (say) 600 
pounds per head.  But for how long?  Assuming that animals are 
normally culled from milking herds before they reach 10 years old, 
we are looking at a three year campaign, costing (the taxpayer?) 
roughly 600*15000*52*3 = 1.5 billion pounds over three years.

My concern is: what will be gained by this expenditure?  Will BSE 
have been eradicated to the satisfaction of both the consumers and 
the veterinary bureaucrats in Brussels.  The latter have already 
demonstrated that scientific arguments do not necessarily carry 
weight.

The unanswered questions which this newsgroup may like to consider 
relate to re-infection horizontally and vertically.  A farmer with 
a history of BSE in his herd may be tempted by the promise of 
compensation to send cull animals for slaughter sooner than 
normal, before they develop any signs of the disease.  Once this 
happens, any way of tracing routes of infection via vertical 
transmission into offspring calves or horizontally into other 
unrelated members of the same herd will be lost.  Without very 
careful tracking of the offspring and contacts of ALL cases of 
BSE, and their eradication if infected, it seems to me that there 
will be an irreducible tail of 'spontaneous' recurrences of the 
disease into the indefinite future.  With no cheap, reliable in 
vivo test for BSE, a slaughter policy may make a bad situation 
worse because evidence for infection tracking will be lost.

I have read claims that BSE prions have been detected in manure, 
although it was not revealed how, or whether this originated from 
living animals with BSE or from residues from already-infected 
food. Other potential vectors for infection may exist.

Note that in the public's perception words such as threat, risk, 
have been redefined in the context of BSE: at the present panic 
level, I suspect that even 'whole life' infection rates of 1 in 
10000 or 100000 would not be acceptable. (ie. one animal out of 
those numbers in the national herd developing BSE at some time in 
its life.) On the evidence available, is BSE sufficiently 
infectious horizontally or vertically to cause these levels of 
occurrence once infectious material has been absent from cattle 
feed for the whole lives of all the cattle in the national herd?

If there is any chance of the answer being YES, then the proposed 
policy will not be sufficient.  Feeding public opinion with the 
fictitious idea that every risk or threat to life can be resolved 
(and / or blamed on a convenient scapegoat - in this case 'best 
scientific opinion') is very risky in itself - as UK government is 
discovering, like 'riding a tiger', it's OK until you have to stop 
to deliver a promise.  (This could develop into a debate on 'the 
social responsibility of scientists' but my main interest at 
present is the 'spontaneous' reinfection rate issue, which may be 
unanswerable from current knowledge.)

Finally, prions seem to present a sufficient general threat to 
provoke questions such as: what about transmission via blood 
products?  What level of latent CJD infection in a human donor 
population would make use of blood or blood products unacceptably 
risky? Now there's a nasty thought!  cf. HIV, hep-B,C, etc.
-- 

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| john brooks    EMail jbrooks at peeras.demon.co.uk
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