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Eyeball-to-eyeball with mad cow disease

Why mad cow disease is spreading across Europe and what we can do to stop it coming here

The countries of Europe are at war with mad cow disease. Last week the German government ordered the destruction of 400,000 cattle in a draconian attempt to halt the outbreak there. Two weeks ago, a program to destroy 25,000 cattle per week began in Ireland. The Irish expect to destroy 300,000 by June. Infected cows have also been reported this winter in herds in France, Denmark, Poland, Spain, and Italy. Entire herds are slaughtered when one member is found to be infected with mad cow disease. Overall, the European Union plans to eliminate 2 million potentially infected cattle by summer, at an estimated cost this year of $1 billion.

Why does the spectre of mad cow disease still loom over Europe? It has been over 15 years since the outbreak of mad cow disease in Britain led to the slaughter of fully a third of all the cows in Britain, 3.7 million animals. While warnings of the danger posed by infected cows came too late for British consumers, the other countries of Europe had not felt themselves at risk, because all of these countries had banned the import of British beef. In the 1990s, as British citizens began to die of the disease, the rest of Europe watched horrified, glad to have dodged the bullet. Only they hadn't.

What happened? How did mad cow disease spread to Germany and the other countries of Europe? Can it find its way to our shores too? Are the 100 million cattle of our country at risk? Are we?

These are important questions, worthy of serious attention. Many reports are appearing in the American press, some alarming, others dismissing the danger here as remote. To sort through the confusion, it is necessary to clearly understand the nature of the disease, and how it is transmitted. To help, here is a primer on mad cow disease, and my assessment of what we should be doing in America to lessen the danger of an outbreak here.

What causes mad cow disease?

"Mad cow disease" is a fatal and communicable brain disease of cows that has a very long incubation period. Decades after infection, the brains of infected cattle develop numerous small cavities as nerve cells die. The holes produce a marked spongy appearance that gives the disease its scientific name, bovine spongiform encephalopathy (BSE). Central nervous system function is progressively degraded, until death eventually occurs. There is no cure.

Mad cow disease is remarkable in that it is not transmitted by a virus or other microbe. Instead, a protein molecule spreads it from one individual to another!

Proteins are made as long strings, like spaghetti, each then folding itself up into a compact shape. The shape it assumes determines how the protein functions in an organism.

BSE is thought to have started when a key brain protein called a prion made a mistake and folded itself up incorrectly. Tragically, this protein, when it encounters others of the same sort, is able to induce them to refold into this same mistaken shape. A wave of misfolding relentlessly expands through the brain like a chain reaction. And, like a spreading rumor, any brain receiving a copy of the misfolded protein experiences the process anew.

Outbreak of mad cow disease in Britain

Therein lies the problem. Prions from the brain of an infected cow can cause the disease in other cows. Because cows normally eat grass rather than each other, you would not expect prion infection to be a problem for cows. However, until recent years it was the practice in Britain to supplement cattle feed with extra protein, and guess where the added protein came from! Often, from the "rendered" bodies of cows that had died in the field. It would be difficult to invent a more perfect way to spread the BSE disease.

Something was bound to happen, and in the mid-1980s it did. There was a major outbreak of mad cow disease in Britain, with many thousands of cattle affected each year for more than a decade. Some 750,000 infected British cows entered the human food chain as hamburgers, sausages and other meat products before the infected herds were slaughtered and the outbreak among cattle brought to an end.

But the warnings came too late for British consumers. In late 1995 the first human cases of mad cow disease appeared. Two teenagers were diagnosed with a rare disorder, typically of the elderly, called Creutzfeldt-Jacob disease (CJD). CJD has an array of symptoms and brain lesions similar to BSE. The sick teens did not live long. Analysis of their brain tissue revealed dense deposits of prion proteins called "plaques," similar to those seen in BSE-infected cows but very different from what is usually seen in CJD. Researchers concluded that they had died of BSE -- the mad cow disease agent had passed from cows to humans! Doctors refer to this human version of mad cow disease as "variant CJD" (vCJD).

In the five years since then, cases of vCJD have continued to surface. Sadly, the British government's CJD surveillance unit reports that the incidence of vCJD is rising sharply. 14 Britons dies of vCJD in 1999, and 21 Britons last year.

This is very sad news, as it tells us the British are probably in the early stage of an epidemic. While only 90 fatal cases have been reported so far, many more vCJD cases are expected to appear as the prions from all that BSE-infected beef work their way through the British population. Researchers can only guess how many people have been infected. Mathematical models predict 136,000. Other researchers suggest that about 10,000 cases would be a more realistic estimate. Either number is a tragedy.

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