Special Reports On Key Topics In Science And TechnologyBSE and vCJD: Instant Expert

Mad cow disease first appeared in the UK in 1986, when cattle started to exhibit strange symptoms of nervous collapse. Vets pinned down the cause in record time: cows were eating other cows via their feed, and a disease was spreading among them.

The disease, dubbed bovine spongiform encephalopathy (BSE), was similar to one that spread among human cannibals in New Guinea. But all was well: the offending feed was regulated, and that, the public was told, was that.

Brain disease bombshell

Except that was not that, as a UK government inquiry heard in 2000. BSE kept spreading because the rules were not being applied. British beef consumers were assured they were safe, and government ministers were famously filmed handing their children beef burgers.

But the bombshell struck in 1996: eating BSE-contaminated beef was the probable cause of a horrifying new version of the Creutzfeld-Jacob brain disease that, unusually, attacked young people. It was named new variant CJD, and epidemiologists vied to predict the eventual death toll.

So where are we now? It turned out that Britain was unlucky in happening to acquire the wrong mutant prion protein at the wrong time, but also extremely lucky in another way. Unlike the sheep disease scrapie, the rogue BSE prion lurks mainly in cattle's central nervous system, and apparently not in most of the meat people eat. Therefore an early, inspired rule - requiring such high-risk tissue to be kept out of cattle feed, and human food - protected the population from the worst.

There have been 150 cases of vCJD in Britain, with only a few more worldwide, and it appears that only people with one genetic variant of the prion develop the disease. However, far more people may be harbouring the rogue protein. And there may yet be unpleasant surprises in store, including unsuspected links between infection and the previously well-known type of CJD, and unsuspected epidemics in countries that so far simply have not looked hard enough.

Going global
While the UK's epidemic was bad enough, BSE turned out to be far from just being a British problem. Angry protests from government officials followed New Scientist's 1997 prediction that BSE had probably spread all over Europe. Three years later most European nations admitted it, starting with France. After Germany, the rest quickly followed. The EU rapidly imposed draconian measures to halt the spread of the disease and to assess the damage.

The lesson was that if you are not looking for it hard enough, BSE can circulate quietly and virtually invisibly. A lack of controls on potentially dangerous meat products eventually put as many people at risk in other countries as were exposed in Britain.

New Scientist then predicted that Canada and the US were testing too few cattle to find BSE if it was there. Again there were denials. But Canada found an infected cow in 2003, and the US, almost by accident, followed just before the end of that year. Yet as European scientists were quick to point out, both countries showed the same resistance to admitting the obvious, and doing enough testing to assess the problem, as Europe had.

The infection is now a global one. Cattle and feed from infected countries has spread to Japan and across the world.

Cures and treatments
Various approaches are now being pursued in the battle against BSE and vCJD. Preventive measures include vaccines or drugs and treatments for vCJD included a controversial drug, antibodies, a cobra venom therapy and even enzymes from volcanic pools. There are also better methods of confining the infection to cattle and a prion-free cow is under development.

European scientists are worried that BSE has infected sheep, where it would be impossible to distinguish from scrapie and more deadly to people. Every hint that it may be lurking in sheep is being pursued - despite the astonishing bungling of early experiments.

The disease can also spread in blood transfusions, hormones, surgery and tissue transplants. The one possible plus from the outbreak is that scientists now know much more about prion diseases and the strange proteins themselves.

To contain further spread, other countries will have to face up to reality quickly. Fears over lost exports have often delayed this, and so the World Animal Health Organization wants nations with BSE to be able to export beef as long as they have taken the right safety precautions, hoping this will lead to an outbreak of honesty. Whether this happy ending comes true or not remains to be seen.

Debora MacKenzie, 13 December 04