The reappearance of a few cases of Sars in Guangdong province in the past few days reminds us of the great epidemic which was said, at one point earlier this year, to threaten an apocalypse. It led to the sealing of Chinese borders, the cancelling of flights abroad, and the virtual isolation of Toronto where a handful of victims were discovered. Yet, what was the net effect of this new destroyer? Approximately 8,000 people fell ill, and of these, 774 died. That is a world figure, yet it is less than a fifth of those who die annually from influenza in Britain alone. What was the fuss about?

Certainly, Sars was a new disease, its effects hard to quantify at the start. But the way in which it was diagnosed, treated and contained was a model of its kind. The coronavirus that caused it was identified early on, at which point scientists were able to advise on treatment, as well as the best ways of preventing its spread. One thing that became rapidly clear was that most people who contracted it recovered fully. As with flu, those who died were mainly the old and the frail. It was, in short, a well-controlled illness of medium seriousness.

A similar scare is now threatened by the discovery of BSE in America. Within hours of the announcement, there was something akin to meltdown in US cattle farming. Trading of beef futures on the Chicago Mercantile Exchange was halted as almost two dozen countries which together consume 90 per cent of American beef exports banned all trade in US beef and cattle products, putting at risk a $27 billion industry.

And yet the evidence of any threat to human beings from “mad cow” disease is so slight that in any rational scientific forum they would be dismissed as non-existent. It rests on the suggestion that variant Creuzfeld-Jakob disease (vCJD) can be transmitted to humans if they eat infected meat.

In the name of this link the entire British beef industry was brought to its knees in the 1990s, with exports barred and thousands of cattle destroyed at a cost to the Exchequer of £4.5 billion. Predictions of a vCJD epidemic were dire; so much infected meat had entered the food chain by the time BSE was identified that likely deaths among the British public were estimated in the hundreds or even thousands.

Yet what has happened? I checked the latest figures yesterday with the CJD surveillance unit in Edinburgh. Last year there were just 16 deaths attributed to vCJD in Britain, down yet again on the previous year. What is more, the evidence of any link with BSE has slumped from slight to negligible.

Scientists such as the Australian, Professor Alan Ebringer, and the British farmer turned expert, Mark Purdey, have challenged the theory, first advanced by the Nobel prize-winning American virologist, Stanley Prusiner, who claims that BSE is caused by molecules known as prions which could indeed infect human beings. They argue that the cause lies elsewhere, and say the link with vCJD is unproven.

In the latest issue of the Journal of Veterinary Immunology, Ebringer reports on further tests which point to the more likely cause of the disease — an infective microbe called Acinetobacter. His results seem persuasive, but the Government is no longer supporting his research.

Why then are the voices of sanity ignored, while the panic merchants hog the limelight? Most experts blame the media for pumping up medical stories in search of a better headline. That may be partly true. But there is no doubt that we have become a jumpy generation, prone to believing the worst.

Scientists must take some of the responsibility. They tend to play up the risks of an epidemic, lest they be accused of complacency or, worse, a cover-up; their research grants may depend on it. Politicians, for their part, have lost the trust of the public. If they say there is no danger, they are not believed. They are no longer confident enough of the facts to reassure the public, so they hope to look more responsible by emphasising the risks instead.

Lost in the middle of all this is the truth. It is, or should be, the ultimate goal of a rational society, and it is usually a great deal less threatening than we are led to believe.

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