Mad Cows Are Back
Published in BBC Wildlife
magazine April 2001
It should have been dead and buried years ago. But somehow the spectre of BSE keeps rising from the grave. In Britain, where billions of pounds have been spent and millions of cattle slaughtered to stamp out the disease, new cases continue to emerge. The German government, having congratulated itself for escaping the crisis, had to sack two of its senior ministers after BSE roared into life there at the end of last year. Beef from France, which claimed to possess the highest safety standards in Europe, has now been banned by several European nations.
It shouldn't have been too difficult to eliminate BSE from the foodchain. If the disease is simply the result of feeding mashed-up livestock to cows, infecting them with mutated forms of brain proteins called prions, then banning the practice should have brought it to an end. Similarly, if the human form of the disease, new variant CJD, arises only from eating contaminated cows' brains and spinal cords, then their exclusion from the human diet should have eradicated it. But still these horrors haunt us.
Indeed, the official explanation for the origination and spread of BSE and nvCJD leaves a series of massive questions unanswered. Why, for example, has BSE only just begun to emerge in Germany, eight years after meat and bonemeal were banned from cattle feed there? Why have vegetarians succumbed to nvCJD? Why is this disease clustered in certain places when contaminated beef has been so widely consumed?
Only one hypothesis appears to explain these anomalies. It is the work not of one of the hundreds of scientists who have studied the disease, but of a small organic farmer based in Somerset, who has never taken a degree. He could be about to make a lot of important people look very silly indeed.
Mark Purdey began his research into BSE after he noticed what seemed to be a correlation between the use of a farm chemical and the spread of the disease. In 1982, the Ministry of Agriculture forced all cattle farmers to start treating their animals with an organophosphate pesticide called phosmet, at far higher doses than are used elsewhere in the world. The pesticide had to be poured along the spine to kill warble fly maggots, which burrow into the animal's hide. At first, Purdey believed it was simply the phosmet, entering the nervous system through the spinal cord, which caused BSE.
But his research soon suggested that this explanation was inadequate. While the use of organophosphates and the emergence of BSE did appear to overlap, the story began to look more complicated. He decided to start again. He decided to visit all the places in which BSE-like illnesses were clustered, to see if there might be a common factor. His results were astonishing. Everywhere he went he found a similar pattern: the humans or animals suffering from these diseases had been exposed to both a surfeit of manganese and a deficiency of copper.
In Iceland, he found that sheep reared in some volcanic valleys had a long history of scrapie, which is the sheep equivalent of BSE. Though low in copper, the vegetation in these places contained two and a half times the usual level of manganese. In adjoining valleys where scrapie had never been reported, manganese levels were normal. In Sardinia, he found that eleven flocks of sheep, grazing on copper-deficient soils, had been treated with manganese oxide. All of them had succumbed to scrapie, while no other sheep on the island had been affected.
In Colorado, he found that BSE-like diseases suffered by deer and elk were reported soon after their populations reached unsustainable levels. Overcrowding had forced them to feed on pine needles, which had bio-accumulated manganese from acid rain. In parts of the copper-deficient Orava Valley in Slovakia, Purdey found, one in a thousand people have contracted CJD. They live downwind of two huge ferro-manganese plants.
As Purdey read about prion proteins, he found that they have two interesting properties. The first is that they are unevenly distributed in the brain, being heavily clustered just under the skull and, in particular, behind the retina. Why should that be? Was it possible that they were defending the brain from some damaging agent which might enter at these points? It is these parts of the brain, Purdey realised, which are most exposed to ultraviolet light, whose levels, in some parts of the world, have increased substantially over the past few years.
The second interesting property of prions, Purdey discovered, is that they bind to copper. In the absence of copper, they would have to latch onto something else. Manganese, if it were widely available, was the most likely candidate. Purdey began to develop a new hypothesis. Prions, he suggested, help to protect the brain by mopping up oxidising chemicals activated by agents such as ultraviolet light. If they are exposed to too little copper and too much manganese, they lose this function, with the result that either the brain is damaged directly by the oxidising molecules, or the prions scramble, triggering further damaging changes in the structure of the brain cells.
And suddenly it all became horribly clear. One of the properties of phosmet, Purdey knew, is that it captures copper, rendering it unavailable to biological systems. If copper were removed from cows' brains, the prions would grab another mineral. Through most of the seventies and eighties, cattlefeed was supplemented, disgustingly, with chicken manure. Chickens are fed manganese to increase their production of eggs. Today, farmers add manganese to cattle feed deliberately, as it encourages cows to absorb extra amino acids. Purdey had, he believed, an explanation for BSE in Britain. But could his hypothesis account for the emergence of nvCJD?
Britain has three main clusters of nvCJD: in the Weald Valley in Kent, Armthorpe in Yorkshire and Queniborough in Leicestershire. At first Purdey thought he would have to abandon his hypothesis, for he soon found that in all three places the soil is deficient in manganese as well as copper. Then he discovered that in 1987 the official farming consultancy ADAS had started advising farmers in manganese-poor areas to spray their crops with the mineral in both autumn and spring, significantly increasing the dose. The Weald is also a major fruit and hop growing area where farmers use organophosphate pesticides, which capture copper, and manganese-based fungicides. Queniborough used to house a major dyeworks. A few years ago, it caught fire, spraying chemicals over the village. Dyeworks use loads of manganese.
You might have imagined that a government confronting a multi-billion pound public health disaster would be interested in findings like this. But Britain's Ministry of Agriculture has sought so far only to rubbish Mark Purdey. Other people have taken an interest however: since he began publicising his hypotheses, he has been shot at, his phone lines have been cut and his house has been burnt down. But the man who, until recently, was ostracised by the scientific community is suddenly enjoying a measure of credibility. Last year he published his first scientific paper, in the respected journal Medical Hypotheses. Now his ideas are beginning to be investigated, with fascinating results.
Last year biochemists at Cambridge, led by Dr David Brown, published a paper showing that when copper was substituted by manganese in prion proteins, the prions adopted precisely the distinguishing features which identify the infective agent in BSE. Now both he and a team of French researchers have separately tested the brains of CJD victims, and found that they contain around ten times as much manganese as the brains of unaffected people. New research by Professor Michel Bounias of the University of Avignon, which has yet to be peer reviewed, suggests that there is a direct link between the spread of BSE across France and the use of a pesticide to kill warble flies in cattle. In January, Purdey submitted a new funding application to the Ministry of Agriculture, and this time it seems prepared to give him serious consideration.
Mark Purdey accepts that the horrible practice of feeding dead animals to cows has a role in the development of the disease. But it cannot, he argues, explain its origination, or that of similar illnesses all over the world. His evidence is, of course, circumstantial: no causal link has yet been demonstrated. But at the very least it is worthy of thorough investigation. Could it be possible that a self-educated Somerset farmer has cracked one of the most important scientific puzzles of our age?