We should spare his neighbours' cattle until we know how prions destroy the nervous systemby John Maddox / May 20, 1996 / Leave a comment
My neighbours in Wales have spent 20 years creating a well-bred herd of beef cattle which regularly wins the prizes at local and even national shows. Most of the animals would go in a cull of all cattle older than 30 months, yet there has not been a single case of BSE in the herd. Waiting to hear what the government decides to do, the family gets what cheer it can from reports that a trickle of cattle is changing hands at the local auction rings.
Disbelief in the danger to human beings from BSE (bovine spongiform encephalopathy) is understandable. It is like radioactivity: how might something that cannot be seen, be fatal to human beings? Pasteur’s germ theory of disease encountered the same scepticism at the outset. So the farmers ask why, if scrapie in sheep is not a hazard to people, beef should be under a cloud because of BSE?
The Pattison committee advising the government on BSE is right to insist that the ten cases of the human analogue of the disease, Creutzfeldt-Jakob disease (CJD), which triggered the present crisis are only circumstantial evidence that BSE has caused CJD. That will remain the position however many (or few) new cases appear in the months ahead.
In recent years, fears that BSE might cause CJD have been met routinely with the declaration that there is “no scientific evidence” that the infectious agent can jump from one species to another. Now people understand that the claim means simply that there is no evidence-one way or the other.
Different parts of animals infected with BSE have been used in feeding trials, which is the basis for banning brain, spinal cord and spleen from the human food chain. The muscular parts of animals that butchers turn into steak fall below the detection level. But they are full of the nerves required to activate muscles, and may still be dangerous.
But how dangerous? The crisis in the beef industry would be less serious if the government had been in the habit of saying that there may be a risk from eating beef, but that at the worst it can be only small. The worst case would be that one’s chance of getting CJD from eating beef is proportional to the number of infectious molecules ingested in the process and that infectious molecules are uniformly distributed in nervous tissue.
My guess is…