The brains of infected people gradually become sponge-like; they become demented and then they die. The first victim was an eighteen month old British boy named Stephen Churchill. He started hallucinating, and his movements became jerky. He lost weight and finally died in 1995.

According to Dr Martin Zeidler, from the CJD Surveillance Unit in Edinburgh, "Most patients with CJD -- are severely demented so that they're unable to communicate. They're usually mute, lying in bed, unable to move and they have jerking movements of their limbs known as miacronis. They can also not infrequently be blind and even though they can't see, their brain is producing hallucinations which can make them very frightened."

The disease produces similar symptoms in cattle. The animal starts to stagger and become easily frightened, presumably because of hallucinations. He or she then leaves the rest of the herd and gradually wastes away.

How did it start?

However, another theory suggests that organophosphate pesticides could be to blame. Mark Purdey, a farmer from the British county of Somerset, presented evidence to the government BSE inquiry suggesting that the disease started in the UK because of the use of phosmet. Phosmet is an organophosphate nerve toxin developed by the Nazis which was used to treat warble fly in cattle. Although the substance was used all over the world, it was compulsory in the UK, and was used at much higher concentrations than elsewhere. It was also used systemically rather than topically in the UK, thereby enabling it to enter the animals' nervous systems.

Purdey has shown that diseases similar to BSE typically occur in areas of high manganese. This is true for scrapie in sheep, which has a high incidence in Iceland, and Chronic Wasting Disease, which is found in elk and deer in Colorado and Wyoming. According to his theory, an excess of manganese and a lack of copper in foetal cattle lead to the creation of prions. Phosmet would facilitate this process by binding to copper and thereby upsetting the balance between copper and manganese. David Brown, a chemist at the University of Cambridge, recently confirmed this.

How is the disease spread?

According to a briefing to the House of Commons, in the late 1970s, rendering plants in the UK were under pressure from the Ministry of Agriculture, Fisheries and Farming (MAFF) to reduce their costs. They reduced the temperature at which they processed the material and stopped using solvents to remove excess fat. Government scientists believe that these changes allowed scrapie to pass from sheep to cattle. Purdey believes that the changes would also have facilitated the accumulation of phosmet in second and third generation cattle.

Will it spread outside Europe?

According to research by the British Broadcasting Corporation, BSE has occurred in at least eleven countries. New Variant Creutzfeldt Jakob Disease (nvCJD) has been found in the UK, Ireland, France and Germany. The UK has by far the greatest number of cases, at around 250,000. However, the disease has also been reported in Canada, Kuwait, Oman and the Falkland Islands. So far, cases outside Europe have only involved animals imported from Britain.

The US has banned British beef and animal feeds since 1991; more recently, China, Australia, Saudi Arabia, Argentina and Japan have banned beef from all countries in the European Union. However, these bans are probably far too late: nor do they include a number of cattle by-products which might also be infectious.

For example, the US did not ban rendered cattle products until December 2000. Even then the ban only covered those countries which were "designated to be infected" with BSE. However, the history of BSE is that countries do not admit that their herds are infected until years after the disease first appears. According to the Sperling Biomedical Foundation, France, Germany, Belgium, Spain, Portugal and Denmark were all years late in admitting that they had a problem. This means that material from infected cattle is almost certainly still finding its way to US consumers.

Nor is there any reason to suppose that an import block would prevent the disease from starting. Dr Francois Meslin, chief of the WHO Veterinary Public Health Unit, says that the conditions for the epidemic which took place in the UK are not unique.

"You need a country which has an important livestock industry, which has a rendering industry and which has animal feeding practices which include the use of meat and bone meal derived from rendering. And those conditions exist in most highly developed countries."

Are there passive carriers?

The Royal Society, the most prestigious scientific body in the UK, has produced a study suggesting that the total death toll could reach 13 million, or about 22% of the UK population. Professor Richard Lacey, a leading authority on the subject, has suggested a figure which is much lower, but still frightening: 500,000, or about 1% of the population.

These figures may be alarmist. However, recent research from Australia has demonstrated that animals can be passive carriers of the disease.

Andrew Hill, a researcher at the Medical Research Council Prion Unit in London, injected 20 normal mice with brain material from hamsters who had died from a form of scrapie. The mice remained healthy. However, Hill then killed these mice, and fed their brains to another set of mice and hamsters. Within four months, the animals had developed signs of a disease similar to BSE: their brains were found to be spongy and full of holes. Moreover, the prions in these animals were different from the prions in the original victims. These experiments showed first, that scrapie could be passed on to other species; and second, that animals who show no sign of the disease could pass it on to others.

A more sensitive test developed in Switzerland suggests that the extent of BSE could be a hundred times greater than previously thought. The Swiss Veterinary Office has been using a test developed by Prionics, a company based in Zurich. This uses an enzyme to break down all the other proteins in the sample apart from the one which becomes distorted in BSE.

The fragments are then separated using electrophoresis. In an investigation in 1997 reported in New Scientist, the true rate of infection in Switzerland was 4.5 per thousand animals, a hundred times higher than the proportion of animals actually showing symptoms. According to Bruno Oesch, head of Prionics, "1800 subclinical cases may have ended up on the table in Switzerland" in that year alone.

Government Cover-ups and Stifled Research

For example, Professor Anderson at Oxford co-authored a study which looked at the infection rate in samples of extracted tonsils. He was fired, supposedly because he speculated about how a friend of the new zoology professor was given a prestigious appointment.

According to the Sperling Biomedical Foundation, there are many other examples of work into BSE/nvCJD being stifled. For example, London Zoo apparently fired its research chef on the orders of MAFF and the Medical Research Council (MRC) after he discovered "too many" species at the zoo had BSE. David Brown, the researcher mentioned above who confirmed the link between phosmet and copper binding, also had his funding removed.

Further evidence that governments know more about the disease than they admit publicly came in a curious statement by the French Agriculture Minister, Jean Glavany. Glavany said in an interview published in Le Monde that there might be a "mysterious third way" by which BSE could be transmitted.

It may seem premature to extrapolate from 90 deaths in the UK to millions of deaths worldwide. However, the people making these claims are serious scientists. The evidence to date is that governments have been slow to admit to problems that do exist, and quick to stifle research into problems that could exist in the future.