Science Interviews


Sun, 14th May 2006

What Is Bse And How Is it Spread?

Professor Tony Minson, University of Cambridge

Part of the show BSE, Cervical Cancer and Toxoplasmosis

Chris - Can you just tell us, what actually is BSE?

Tony - The disease is a disease that causes paralysis, coma and then death: it's a central nervous system disease. It's one of a group of diseases of this kind, but BSE is special because it appeared out of the blue in cows in the late 1980s. From almost nowhere it got to about 40 000 cases per year by around 1990. What was really horrible was that it proved to be transmissible to people but extremely inefficiently. So it turns out that there have been about 100 cases all told in the last ten years in people but there have been hundreds of thousands of cases in cattle.

Chris - If you zoom in with a very powerful microscope on the brains of cows and people that have been affected, what is the nature of the infectious agent?

Tony - It's really unusual and it's taken the last fifteen years to show that it's this totally new kind of disease not caused by a bacteria or a virus but by on eof our own proteins folding abnormally. It extremely rarely folds abnormally and then forms aggregates of that abnormally folded protein. It's strange because it seems that this abnormally folded protein that attracts other normal protein and recruits it. If you look at it with a really powerful microscope, what you see is rod - like aggregates of this material and they're the things that are called prions. You hear the term prion diseases, and prion diseases are this group of diseases caused by abnormal proteins.

Chris - It's not just BSE though: there are a whole clutch of these that occur naturally in people and animals and in different forms in people.

Tony - There are many different diseases of this kind. In sheep it's called scrapie; in man we've known for many years about a disease called ordinary-CJD which occurs spontaneously in every population in the world. About one person in a million every year gets CJD where the formation of the abnormal protein occurs spontaneously. Where it gets risky is when you start recycling into the same species. One of the famous example of that is Kuru. In the highlands of New Guinea in a particularly isolated area, they practise cannibalism as part of a funeral rite. When people died, they used to take the brain material and eat it as part of the funeral rites.

Chris - When they were doing that, how was the protein that was in that brain tissue getting into the person's brain?

Tony - When you eat a bit of the brain it goes into your stomach and it passes across the stomach wall into the lymph system. It's thought that in the lymphoid tissue and in the spleen it expands and begins to recruit more of the same protein. Then it appears to go along the nervous system into the brain, all the time recruiting more protein and converting more of the normal protein like a chain reaction. The dangerous thing jis obviously the cannibalism and recycling food back into the same species.

Chris - Is it just unlucky that it happened here in Britain?

Tony - I think that's probably right. I think we were just extremely unlucky because virtually every western country was certainly taking the remains of beef carcasses and then rendering that down into a high-protein supplement to feed back to more cows. So I think it could have happened anywhere.

Chris - So if anything, British beef is now safer than it's ever been, and perhaps we should be suspicious of beef from other countries.

Tony - Well I wouldn't like to say anything about other countries because we will end up getting sued, but I think you're right. We now take extra-ordinary precautions. First of all we don't recycle any bovine material back into the bovines and we don't make meat in bonemeal anymore. Secondly, we don't eat any animal that was born before 1996 when we stopped recycling food completely back into bovines. Thirdly, we remove all the dangerous tissue, such as the lymph and the brain tissue from the carcass before it's butchered and then finally animals are tested for the presence of prions when they go tot the abattoir. So it's an extra-ordinary range of tests that's done. Because we no longer recycle bovine meat into cows, the number of BSE cases in this country is now reducing. It's now a thousand-fold lower than it was ten years ago.


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