The Continuing Threat of Mad Cow Disease
In 1999 the countries of Europe went to war with mad cow disease. The German government ordered the destruction of 400,000 cattle in a draconian attempt to halt the outbreak there. A program to destroy 25,000 cattle per week was instituted in Ireland, destroying over 300,000 individuals. Infected cows were also reported 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 eliminated 2 million potentially infected cattle, at an estimated cost of $1 billion.
How did the spectre of mad cow disease come to loom over Europe? It had 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. With the discovery of a cow with mad cow disease in Canada in May, 2003, 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 an 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 some 100 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. Researchers suggest that about 10,000 cases would be a realistic estimate. Whatever the final number, it is a tragedy.
How mad cow disease spread to Europe
And it seems the tragedy is not over. Mad cow disease went on to spread to Germany and the other countries of Europe. How? Europeans fixated on the infected British cows, and ignored the disease agent. The disease initially spread in Britain because cows were fed protein-supplemented feed -meat and bone meal (MBM) prepared from animals infected with mad cow disease. But although there is a thriving international trade in MBM, nothing was done by Europe to restrict their exposure to meal prepared from cattle that had died of mad cow disease. The European Union waited unhtil 1999 to imposed a six-month ban on MBM, extending its more limited ban on protein supplements.
What should we do to lessen the danger?
Mad cow disease and AIDS haunt the beginning of the 21st Century. The twin terrors of these epidemics are lethality (both are 100% fatal) and invisibility (both reveal no signs of disease until many years after infection). On balance, we have done well in fighting AIDS. Three of the lessons we have learned combating AIDS will serve us well as we now turn to face mad cow disease.
1. Devise a test for the disease agent. Early in the AIDS epidemic, investigators — led by Gallo of the NIH — developed tests for the presence of the AIDS-causing HIV virus. More than any other thing, the mad cow epidemic cries out for that sort of test. Without it, the only sure way to detect the presence of the disease is to sample brain tissue from dead animals. Animals that appear healthy cannot be tested to see if they harbor the disease-causing prion.
A few researchers are reportedly at work trying to devise such a test. Our country cannot afford to sit around waiting. The federal government should immediately make the development of such a test a national research priority. Focusing many excellent minds on this key goal will increase the probability of a quick solution.
2. Focus on prevention. If we are to prevent mad cow disease from reaching our shores, it is important that we not make the same mistake that doomed Europe to today’s epidemic. Regulations should focus not only on cows, but also on the agent that gave them the disease. The prion proteins that cause mad cow disease are present primarily in nervous tissue. Because the skull and spine that make up a large portion of bone meal are easily contaminated with brain and spinal tissue during “rendering,” bone meal prepared from cattle is a real source of danger. Hence the danger of MBM.
As in Europe, regulations in the United States focused first on live cows. In 1989, as the mad cow epidemic surged in Britain, the United States banned imports of live cattle from Britain or other “mad cow” countries. Then, like Europe, we sat back and watched what happened in Britain. It was not until 1997 that the United States banned the supplementing of livestock feed with MBM prepared from cows — nine years after the same ban had been enacted in Britain.
3. Don’t wait to lock the barn door until after the horse is gone. The 1997 USDA regulations still allowed the importing of bone meal prepared from pigs and other animals raised on feed supplemented with cow MBM. This was tempting fate, as it is quite possible (even likely) that the prions that cause mad cow disease can pass from cow to pig and back. Only in December, 1999 did our government enact comprehensive legislation banning imports from Europe or other mad cow countries of all rendered animal protein products like MBM, whether from cattle, pigs, chickens, sheep, or any other animal.
Thus our comprehensive ban of the agents that transmit mad cow disease has been in place for less than three years. We are lucky indeed to have escaped, so far, the devastating outbreak of mad cow disease that imported MBM has brought to European countries.
The Importance of Compliance
The lesson we need to learn is that no magic barrier keeps the disease out of The United States. What will keep it out is a stout barrier of regulation — rules and inspections to protect our cattle industry from importing animals or feed bearing the disease. Our current regulatory barrier is well-thought-out, if tardy. There is little doubt it can be effective.
However, a rule is only as effective as its enforcement. Disturbingly, recent checks have shown the barrier of regulations meant to protect us are often ignored. The Food and Drug Administration reported in 2000 that a quarter of the 180 large American companies involved in manufacturing animal feed are not complying with regulations meant to prevent the spread of mad cow disease in this country.
This lack of compliance is scary. Marianne Elvander of the Swedish National Veterinary Institute is quoted by Reuters as saying “Negligent compliance with the meat and bone meal ban is the main reason for the spread of BSE in Europe.” FDA veterinary chief Dr. Stephen Sundlof issued a statement agreeing: Europe’s mad cow crisis “is not a result of them not having adequate regulations in place — it was a problem of enforcement.”
These FDA regulations are our only firewall against American mad cow disease. The FDA has warned that continued violations will prompt company shutdowns and prosecutions. Exactly right. Americans could sleep better if the FDA immediately announced a plan to dramatically increase its surveillance of compliance with those regulations. They need more inspectors, if a quarter of the feed companies are not following the rules.
Should we stop eating meat, like many are doing in Europe? No. There is no evidence of a problem here now, only a nagging worry. If our government does its regulatory job, then Americans will be able to eat the steaks they love with no worry, and hamburgers too.
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