Mad cow: worse than you think


In December, a US Department of Agriculture (USDA) veterinarian discovered that a cow imported from Canada into Washington state tested positive for the invariably fatal Mad Cow disease. Two months later, the USDA quietly concluded that it had failed to find as many as 80 animals from the same herd that may also have been infected. The admission of failure, drowned out by a ridiculous Super-Bowl-related controversy, slipped nearly unnoticed past the public.

This was an unbelievable stroke of luck for the USDA. On a slower news day, the admission that dozens of potentially infected cattle had disappeared into the American food chain might have prompted a wave of panic, spurred by memories of the 1990s Mad Cow catastrophe in the United Kingdom. Reassurances from Secretary of Agriculture Ann Veneman, echoed by beef industry trade associations, bore a striking resemblance to the PR palliatives that issued forth from British officials before that country’s epidemic, during which more than 100 Britons died in agony from contaminated beef. Veneman’s characterization of increased testing and a ban on “downer cows” entering the food supply as a “very aggressive” policy neatly paralleled former UK agriculture minister Angela Browning’s December 1995 claim that her agency’s standards were “ultra precautionary.”

The ban on downer cows was long overdue. For a decade or more, US food safety activists had been urging a complete ban on downer cows being slaughtered for food. “Downer” cows are unable to walk, a warning sign of Mad Cow disease. The ban by the USDA was widely seen as a move to blunt criticism for agency foot-dragging on more thorough testing for infected cattle. In any event, workers at the slaughterhouse in Washington where the sick animal was found have disputed the USDA’s statement that the cow was a downer. If they are right, a downer ban would not have kept the cow from being ground up for your Happy Meal.

Veneman’s foot-dragging extends to more than the ban on downer cattle. The Secretary of Agriculture has also helped delay implementation of mandatory Country of Origin Labeling (COOL) for agricultural products. The labeling law was passed by Congress in 2002 as part of the farm bill, and would have taken effect in September of this year. Such labeling would have helped track down the rest of the suspect Canadian cattle herd. With Veneman’s vociferous backing, a two-year moratorium on COOL for beef, pork, lamb, peanuts, and fresh fruits and vegetables, hidden in an omnibus appropriation bill, passed the Senate in January.

More ominous is the USDA’s recalcitrance when it comes to testing for Mad Cow. To boost confidence in US beef after several trading partners stopped importing it, Veneman announced in February that the USDA would double the number of US cattle tested each year to 40,000. In March, she raised that number to around 60,000, and then to several hundred thousand. Thirty-five million cattle are slaughtered for consumption every year in the US: the USDA’s accelerated “very aggressive” testing would cover one or two percent of them.

A senior USDA scientist, speaking anonymously, told the New York Times that the USDA has fallen into lockstep with a broader Bush administration policy of suppressing science in order to boost industry profits. The USDA whistleblower pointed out that top Agriculture brass also pushed for importation of Mexican beef infected with bovine tuberculosis, a move that devastated the formerly TB-free Texas beef industry. The agency also pushed its scientists to approve the importation of fruit from China infected with a fungal disease. In August, Veneman minimized the threat from boneless beef, saying, “our experts have determined that the risk to public health is extremely low.” “That really frosted me,” the anonymous scientist told the Times, “that she said we’d done [the research] when I knew in fact that we hadn’t.”

In March, a pending House bill to institute a $175 million national livestock identification system to better track suspect cattle was criticized by Agriculture Undersecretary William Hawks, who said the program should be voluntary when implemented and become mandatory at an unspecified “later date.” “The marketplace should be the driving force” behind any such program, Hawks told a House subcommittee.

Even if the USDA were to test a majority of cattle, push for COOL, and start trusting its scientists, there’s still a strong chance that Mad Cow disease could kill Americans. Some analysts, in fact, wonder whether it might already have killed thousands, misdiagnosed as early-onset Alzheimer’s or multiple sclerosis. And if recent studies of the alleged Mad Cow causative agent turn out to be correct, even the “aggressive” Mad Cow measures proposed by some USDA critics may prove insufficient to protect the health of the American public.

The human form of Mad Cow disease, more formally known as new variant Creutzfeld-Jakob Disease (nv-CJD), is a chronic and incurable deterioration of the central nervous system, one of a larger class of diseases called transmissible spongiform encephalopathies (TSEs). It is widely accepted that nv-CJD is caused when people eat certain kinds of tissue from cattle infected with a TSE called bovine spongiform encephalopathy (BSE).

TSEs occur in a number of animal species. Scrapie infects sheep, and was first noted in Europe in the 18th century. Chronic wasting disease afflicts deer and elk in North America. Some TSEs appear to be inherited, while others seem to strike their victims randomly.

TSEs are generally rare, with a normal rate of around one case per million animals. But this changes when infected animals are fed to other animals. TSEs that would otherwise die with their victims are passed on when those victims are eaten. As reported in Earth Island Journal in 1996, the beef industry drastically amplifies the risk of Mad Cow by feeding “bypass protein”—a protein-rich cattle feed designed to encourage high milk production—to dairy cows. Though cattle are naturally vegetarians, bypass protein usually contains animal byproducts, mainly supplied by rendering plants, factories that turn dead animals into industrial feedstock. One sick cow rendered into protein meal could theoretically infect thousands of dairy cows with BSE. When they reach the end of their productive lives, most dairy cows are shipped to slaughterhouses to begin new careers as ground beef.

The vast majority of scientists agree that the culprit behind TSEs is a “rogue protein” called a prion. The non-infectious form of the prion protein is found in association with nerve cells, and is thought to play a role in the transmission of impulses from one nerve cell to another.

Proteins are long chains of simpler organic molecules called amino acids. At each link between amino acids, the protein chain can bend in several different directions. Whether or not a protein molecule is useful depends in part on the molecule’s shape. Infectious prions are folded differently from the benign form and are likely useless for whatever function the benign form fulfills.

The jury is still out on the exact mechanism by which TSEs cause nervous system damage. Some researchers believe that the rogue prions cause benign prion proteins to fold the wrong way by their mere presence. Others postulate a catalyst, an as-yet-undiscovered “Protein X,” that helps rogue prions convert benign prions. A few scientists still resist the idea of prions as pathogens, and are looking for a “slow virus” causing TSEs, of which prions would be a mere side effect. This much is indisputable: TSEs involve severe and fatal nervous system degeneration, found in association with rogue prions, and TSEs’ main method of transmission is the consumption of infected tissues.

More than just nerves?

Conventional wisdom says that nervous system tissue is the only part of the cow that poses a Mad Cow risk to consumers. The USDA backs this assumption, and has banned human consumption of those parts of cows older than 30 months most likely to contain central nervous system tissue.

But research done over the last few years by Stanley Prusiner, the University of California scientist whose work on prions earned him the 1997 Nobel Prize in Medicine, suggests that the risk may well extend to the entire animal, including the skeletal muscle (a.k.a. “steak”) now deemed safe by the USDA. Prusiner inoculated mice with Mad Cow prions and found prions in the infected mice’s skeletal muscle. He published his findings in a National Academy of Sciences paper in 2002; a subsequent German study corroborated his work.

Prions may react differently in mice than they do in cows, the USDA warns. It may be that some unknown factor—perhaps the mysterious “Protein X”—facilitates prion replication in mouse muscle, but is lacking in cow muscle. Prion science is still in its infancy, and more is unknown than is known. The World Health Organization claims that skeletal muscle from cattle with full-blown BSE is completely safe to eat—providing that meat is processed in a way that prevents contamination with nerve tissue. But these statements are based on preliminary science and tests that may well prove to be inadequate after further study.

For example, in February, a team of Italian scientists claimed they’d found a form of prion-related Mad Cow, potentially transmissible to humans, that would have evaded the USDA’s current testing regimen. This new disease, rather than creating large, spongy holes in cow brains, caused the formation of “amyloid plaques”—accumulations of sticky proteinaceous matter in the brain. The researchers conjecture that some forms of sporadic Creutzfeldt-Jakob Disease, a human disease similar to but distinct from nvCJD, could be contracted by eating such cattle. A beef cow with a fatal case of this new TSE would pass the USDA’s tests with flying colors.

What’s more, the USDA’s policy of banning central nervous system tissue for human consumption from just those animals older than 30 months has come under criticism. The USDA claims younger animals have not had sufficient time to develop Mad Cow. But in February, Japanese scientists found two calves, aged 21 and 24 months, with Mad Cow Disease.

Finally, the USDA’s 1997 ban on animal products in feed for cattle, enacted in the wake of the British disaster, stops far short of what most scientists agree would prevent transmission of TSEs to human meat-eaters. Since 1997, it has been illegal for US cattle feed to contain any cattle byproducts. However, it’s still legal for dead cows to be fed to non-ruminant animals, such as pigs, which can then be rendered and added to dairy bypass protein, with the prions coming along for the ride. (Pork may not be a good beef alternative for worried consumers, as most pigs are slaughtered at 30 months, well before TSE symptoms would likely show up, and “downer” pigs are regularly slaughtered for human consumption.) Experts, such as researcher Carleton Gajdusek, who studied kuru—a prion disease found in New Guineans who ate human flesh—think that chickens may represent another vector by which cow prions can infect humans, if the chickens are fed contaminated meal.

Problems are inevitable when the USDA, the agency responsible for regulating the beef industry, is also charged with promoting the beef industry. Were it not for this inherent conflict of interest, a few common sense steps would likely sail through the agency—steps that food safety advocates ranging from small-scale ranchers to the National Farmers’ Union to Senator Tom Daschle now demand:

  • Ban all feeding of animal byproducts to animals intended for human consumption. Protein supplements derived from plant sources, for instance, might cost more and lessen milk production slightly, but dairy farmers are already heavily subsidized, with most of their production going to industrial use such as casein and processed cheese. Our society can easily bankroll the slight increase in cost to farmers that a ban on feeding animal products to meat animals would entail.
  • Test all cattle at the slaughterhouse. The US wouldn’t be the first nation to do so: Japan already tests every cow arriving at its slaughterhouses for TSEs. A California lawmaker has introduced a bill to mandate testing of all cattle slaughtered in the state.
  • Enact a temporary ban on human consumption of brain and nerve tissue. Until any animal that might have eaten animal byproducts is moved through the system, such a ban would protect us from “stealth” prions in younger, asymptomatic cattle.
  • Enact Country of Origin Labeling (COOL) for meat. Even after the above stringent measures are enacted, infected beef imported from other countries will still pose a threat to consumers. COOL provides a market-based solution to that problem, allowing consumers to make informed choices about the food they eat.
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