Disturbing questions about what's on your plate surfaced Dec. 23, when the U.S. Department of Agriculture (USDA) announced that a dairy cow that was cut up for meat in Washington State on Dec. 9 had mad cow disease.
This BSE-infected cow shows some hallmark symptoms of the disease: abnormal posture, difficulty standing, and weight loss. Photo by Art Davis, USDA.
The TSEs cut holes in the brains of people and other mammals, making them look like sponges (hence the bloviated term "spongiform encephalopathy"). TSEs are incurable and always fatal.
To date, the mad-cow epidemic has killed about 140 Britons since 1995. Eventually, at least 200,000 British cows -- perhaps 1 million -- went mad.
Economically, BSE skinned and boned the British beef industry. Could it eviscerate the $27-billion U.S. industry?
As federal officials scrambled to recall meat that may have been eaten by people in six states, mad cow made irresistible headlines. A late December survey by the National Cattlemen's Beef Association found that 96 percent of consumers -- practically every American not in a vegetative state -- knew something about the disease, up from 61 percent in September.
The survey found that American consumers remained confident in the safety of beef. And certainly, mad cow is peanuts compared to other food-borne illnesses, which "cause approximately 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths in the United States each year," according to the Centers for Disease Control.
Mad about mad cow
Still, mad cow is scary. Overseas, more than 30 countries have banned imports of U.S. beef. In Japan, "Senior Japanese officials on Tuesday were sharply critical of U.S. efforts to guard against the disease," Reuters reported on Jan. 6. "'The U.S. safeguards are not up to the level of those (in Japan),'" said Agriculture Minister Yoshiyuki Kamei. In 2001, Japan reacted to a small BSE outbreak by testing every animal before it becomes meat.
As the bad news rolled on, prices fell. On the Chicago Mercantile Exchange, the price for February delivery of finished beef cattle fell from $0.91 per pound on Dec. 23 to $0.74 on Jan. 6.
Faced with headlines, doubts and import bans, the beef industry reversed itself and agreed to stronger regulation. An industry that had long opposed the importation of beef from a country with mad cow disease urged the U.S. government to push other countries to import beef from the United States, a nation that now has mad cow. On Jan. 1, Reuters noted that "In the past, nations could expect lengthy cut-offs in trade once mad cow disease was discovered," adding that the United States had halted beef imports from Canada after mad cow was discovered there in May, 2003.
Beef. Is it still for dinner?
For its part, the USDA had to admit that its rules had failed to prevent the entry of BSE and explain why it suddenly favored a ban on downer cows. According to the Washington Post, "The Agriculture Department's announcement yesterday of a ban on the sale of meat from ailing 'downer' cattle marked a policy turnabout for the Bush administration, coming only a few weeks after the department and allies in the powerful meat lobby blocked an identical measure in Congress.
On Dec. 31, the day that article was published, Secretary of Agriculture Ann Veneman gamely explained her position. "For more than a decade, the United States has had in place an aggressive surveillance, detection and response program for BSE. While we are confident that the United States has safeguards and firewalls needed to protect public health, these additional actions will further strengthen our protection systems."
The key regulatory tactic is to keep brain, spinal cord and a few other tissues out of the food supply, since that's where the BSE infection is concentrated. Beyond tightening restrictions on tissues known to carry mad cow, USDA will, for the first time, ban what it delicately called "non-ambulatory" -- downer -- cows from the human food chain.
The costs of inaction
With its members' livelihoods at stake, on Dec. 31 the NCBA announced support for the new USDA rules, which would also segregate meat from tested cows until after tests come back clean, and ease disease tracking with a new national registry for beef animals.
Too little, too late, says industry critic Michael Greger, a medical doctor who covers the issue for Farm Sanctuary, an "animal-protection" group, and Organic Consumers, which promotes organic agriculture.
Greger sees serious loopholes in the new regulations. For one thing, he says, Veneman said nothing about increasing the rate of testing. For another, the USDA will continue to permit the processing of slaughterhouse waste into animal food. Blood meal, for example, can still be fed to cows and calves. And chickens, pigs and fish can still eat many types of ruminant wastes.
Feeding animal parts to animals caused the BSE epidemic in Great Britain. We'll examine whether the United States could repeat the British bungle.
What's the story with mad cow?
When mad cow disease broke on the British isles in the mid-1980s, the government responded to the specter of cows that showed (as the USDA now describes the symptoms) "changes in temperament (e.g., nervousness or aggression), abnormal posture, incoordination and difficulty in rising..." with reassurances. Not to worry, mad cow did not threaten people. After all, it was just another version of scrapie, an old sheep disease that people never caught.
But not even a cabinet minister's public devouring of British beef could prevent mad cow from infecting humans. Since 1995, about 140 Britons have been diagnosed with variant Creutzfeldt Jakob disease -- a human TSE that's blamed on eating meat from mad cows. Death comes in six months.
To put the matter in perspective, millions of Britons ate beef during that period. Nevertheless, in the United States, which we have been repeatedly assured has the world's safest food supply, that risk is difficult to swallow.
Abnormal history
Scrapie, the first TSE, began killing sheep in Europe and Great Britain in the 1700s. In the 1920s, doctors Creutzfeldt and Jakob began exploring a rare, fatal human brain disease that ripped holes in the brain. In the 1960s, another version of this disease showed up in a New Guinea tribe that ritually ate deceased relatives.
Until the 1980s, the TSEs remained an obscure problem, but a baffling one. Although they were infectious, the cause of the disease could slip through a filter that would trap bacteria. That pointed the finger at a virus -- but the agent survived treatments that kill all viruses.
Compounding the problem is the long incubation period. In cows, for example, BSE is unheard of in animals younger than 30 months, which explains the emphasis in this country on testing only older animals.
TSEs hit the headlines in the 1980s and 1990s, when British cows began going mad. In 1995 and 1996, a group of unusual cases of CJD tipped off doctors to the emergence of what's now called variant CJD. Immediately, suspicion focused on eating meat from mad cows as the cause, and that suspicion is now the accepted wisdom in terms of cause. By the end of 2003, 137 cases of variant CJD had appeared in the United Kingdom. The rate of new vCJD infections is declining, from a high of 28 in 2000 to 16 in 2003 (as of Dec. 1).
Why was British beef so infectious? Partly, it was the huge size of the problem, with the number of mad cows eventually eaten numbering at least in the thousands. But it's also what was eaten. Most scientists think British beef contained parts of brain or spinal cord, where diseased prions are concentrated.
And thus a key consumer-protection strategy has been to exclude these tissues from meat. Muscles contain no prion -- or so goes the accepted wisdom.
A muscular disease?
But Stanley Prusiner, the Nobel-winning neurologist and biochemist at San Francisco State University who identified prions as causing TSEs, casts some doubt on the "nervous-system only" theory. In a 2002 study, Prusiner and colleagues found prions in the muscles of mice they had infected with TSE prions. In a press release, Prusiner said, "Whether prions accumulate in the skeletal muscle of other animals remains to be established. But our findings indicate the need to carry out a comprehensive and systematic investigation of the distribution of prions in the skeletal muscle of animals who develop prion diseases."
Perhaps because it's been, until recently, extraordinarily difficult to test for small concentrations of prions, the medical literature includes few studies of the matter. A report published this month found no abnormal prions in the muscle of 20 cattle, sheep, elk, and raccoons that had been experimentally infected with TSEs.
However, another study reported this month found "abundant disease-associated prion protein" in the muscle of a patient with sporadic CJD. And a study published last fall (see "Extraneural Pathologic Prion..." in the bibliography) found abnormal prions in the muscle of 8 of 32 CJD patients.
That study, said Nature, "resurrects the idea that BSE-infected cows might harbour trace levels of prions in their muscle meat. He [researcher Adriano Aguzzi] plans to use his sensitive test on cow tissue to see if he can pick up prions." However, Nature concluded, "All other evidence so far suggests that cow muscle is not infectious. 'You can rest assured that this has been looked at,' says Neil Cashman," a prion researcher at the University of Toronto.
Since, in searching back to 1998, no other studies listed in PubMed (when searching for "prion muscle") appears to specifically address the presence of abnormal prions in muscle. As the authors of the above-mentioned negative study of 20 animals concluded, in a sentiment that may apply to the whole issue, "Further testing of muscle tissues is needed to confirm the findings of the present study."
Mad-cow Nobel
In the 1980s, it was Prusiner who finally developed the prion hypothesis to explain mad cow and other TSE diseases. Scientists had recognized for years that the cause of TSEs broke the rules Although the diseases are infectious, the causative agent, unlike that for any other known infectious disease, contains neither DNA nor RNA.
As Prusiner and many of his former skeptics see it, prions are normal proteins that somehow fold into a decay-resistant, infectious shape that somehow causes chain-reaction misfolding among other normal prions. Eventually, the growing mass of misshapen prions somehow kills nervous tissue, cutting holes in the brain and causing fibrous plaques that resemble those seen in Alzheimer's disease.
In cattle, humans, mink, deer, elk and sheep, the TSEs go thru a long period of incubation and then cause neurological decline and rapid death. Today, despite some quite tentative advances in treatment, the only way to deal with TSEs is to prevent them, which, in turn, calls for some cumbersome and expensive changes in the way beef is raised and slaughtered.
Did USDA go far enough?
Responding to the discovery of mad cow last month, the USDA quickly announced a further tightening of the BSE regulations. The tightening, USDA said, reflected an "abundance of caution."
But USDA's tighter regs are still laxer than Europe's, where one-fourth of all slaughtered cows are tested for mad cow, according to the Organic Consumers Association. Writing in the group's website, Michael Greger, a general practitioner in Scarsdale, N.Y., who follows the BSE issue, notes that "France, which has only a fraction of the U.S. cattle population, tests more cattle in a single week then the U.S. has tested in a decade."
Greger sees a number of loopholes in the new, improved regulations, both in terms of slaughtering practices, and the effort to prevent cows from eating cow byproducts.
1: In the blood?
The British mad-cow epidemic was a result of cows eating feed made from the by-products of mad cows. (Presumably, although the issue is debated, the disease first originated in byproducts of scrapie-infected sheep.) Large-scale animal feeding has long featured a massive recycling that solved two problems at once: Disposing of tons of inedible slaughterhouse by-products, and providing another protein and mineral source to farmers for blending in animal diets. Often called "meat and bone meal," these by-products were dried, sterilized and added to many animal feeds. When the rendering industry began work, nobody suspected that an infectious agent could survive the sterilizing procedures.
In 1997, the USDA banned the feeding of many ruminant parts to ruminants, thus interrupting the feed cycle that caused so much misery in the UK. From the USDA's pronouncements, you might assume that no American cow will eat the byproducts of dead cows. But you would be wrong. Ruminant-to-ruminant feeding continues, as does the feeding or ruminant by-products to fish, pigs and chickens. "The other big mad cow in the room is that they're not saying anything about stopping feeding slaughterhouse waste and blood to animals," says Greger. In particular, calves often eat a protein-rich milk replacer instead of milk, which is sold by dairy farmers. And one cheap source of protein is dried blood meal from, yes, ruminants.
Why, Greger asks, is this permissible when a related route of infection is banned in people? For fear of infecting the blood supply, the American Red Cross no longer accepts blood transfusions from people who lived in the United Kingdom during the mad-cow epidemic.
McCarty says the Red Cross is obeying "the precautionary principle, and typically the precautionary principle is not something I strongly support. ... Still, there is no research that says that human TSEs are transmissible by blood, there is a lot of research going on, but it has not been demonstrated yet in humans."
Perhaps, but a PubMed search of the medical literature for "BSE AND blood AND infect?" returned only two articles, neither assessing the potential for spreading TSE through dried blood meal. PubMed carried no articles related to "BSE AND 'milk replacer'".
Does the exception for dried-blood products make sense? Judd Aiken, a University of Wisconsin-Madison professor of animal health and biomedical sciences who studies prions, admits that he knows of no studies showing that cattle blood is infectious, "But I'm not comfortable with the argument that therefore it cannot be infectious."
2: Fed bad feed?
Blood meal is hardly the only cow protein being served to animals. It's still legal in the United States to feed bovine meat and bone meal to poultry, pigs and fish, which have never been seen to catch TSEs. This practice may have made sense a year ago, before BSE appeared in the United States, Aiken says, but it's questionable today. "After the finding of two cases of BSE in North America, arguably there are more cases and there have probably been other [affected] animals already rendered. So we have to change what we have been doing, and have to change it relatively quickly."
Aiken warns that such feed could be deliberately or accidentally fed to cows, or it could be contained in sweepings from chicken-house floors, which cattle can legally eat. Either way, he says, " If any of that material gets into the cattle feed, then we are back to feeding cattle products and bone meal back to cattle." This may sound like paranoia, but the UK epidemic continued even after the government banned feeding ruminant by-products to cows. "In Great Britain," says Aiken, "they very clearly had cattle come down with BSE after the ban, and many of them were in areas where a lot of poultry being raised."
3: Stunning gun?
Effective immediately, the USDA has prohibited the "air-injection stunning" of cattle. Excuse us for getting grisly, but how are cattle killed at slaughterhouses? Following a 1901 federal law that requires "humane" slaughter of cattle, slaughterhouses shoot a metal bolt into the cow's brain, causing an immediate loss of consciousness. That's good. But the bolt can also distribute bits of central-nervous system tissue.
That's bad.
These bolts differ. In air-injection stunning, the bolt is followed by a blast of air that further disturbs the brain, ensuring that the cow does not regain consciousness while it is being "bled out." These air-injection systems may push bits of brain into the circulatory system while the heart is still pumping, interfering with the separation of "specified risk materials," tissue of the central nervous system, and small intestine, where abnormal prions appear early in TSEs.
Air-injection bolts have already been banned in Europe. But how much safer are the captive bolt systems that the USDA favors? It's a good question, as long as you remember that the whole issue is relevant only if meat animals indeed carry diseased prions.
A study published in 2002 found problems with the supposedly safer captive bolt process. The researchers placed a marker bacterium on the bolt, fired the gun, tracked the marker, and summarized their results: "The marker organism, introduced by injection through the bolt entry aperture or directly using a cartridge-fired captive bolt, was detected in the slaughter environment immediately after stunning and in the abattoir [slaughterhouse] environment at each subsequent stage of the slaughter-dressing process. The marker organism was also detected on the hands of operatives; on slaughter equipment; and in samples of blood, organs, and musculature of inoculated animals". Of course, whether the abnormal prion behaves like a bacterium is not known.
Although the Jan. 8, 2004 USDA press release announcing the ban on air-injection did not mention the above study, the Department's notice in the Federal Register did acknowledge that "More studies are needed to determine whether, and if so, the degree to which, CNS [central nervous system] tissue may be present in blood clots observed in the hearts of stunned cattle."
Going down slow?
Finally, here's an irony for you. The USDA has now banned "downer cows" from human food. It's logical to think that eating cows with enough brain damage to interfere with walking would not be healthy. But look closely.
But Daniel Schaefer, a professor of animal science at the University of Wisconsin-Madison, observes that had she not been paralyzed, she would have stayed in her herd. If she later developed symptoms of BSE, she may have been culled from the herd, when she might have well have been fingered for BSE-testing.
Schaefer makes another point about downers: Most have muscular or skeletal problems, not brain disease, and thus should make good meat. "From a PR perspective, the ban on the inclusion of meat from downer cattle in the human food chain is very easy for the consuming public to comprehend," he says. "I think the USDA responded effectively -- with an abundance of caution, but it sometimes erred on the side of public relations rather than on the side of science."
Consider, he says, the effects of the downer ban. The Washington State "downer" would not have been tested if slaughterhouses were not buying downers, which could skewer the effort to detect BSE. "If those animals are considered to be the population that is most likely to demonstrate the symptoms of BSE, it sure would be better to have them within the surveillance system rather than outside it," Schaefer says.
Testing, testing?
So how dangerous is beef? None of the experts we spoke to expected a big, UK-style mad-cow epidemic in the United States, but their takes on the facts did vary considerably. Take one "simple" question: Did testing find the only U.S. mad cow, or just the tip of the iceberg? In other words, is surveillance working?
McCarty, of the cattlemen's association, says the surveillance program was statistically designed to detect an infection level of one animal in one million, and it apparently succeeded at that.
But Greger says we will not know the true extent of the disease "until we do better testing. I'm afraid that's what the industry has been counting on. They have been resistant to increased testing for a decade, and from their perspective, it makes sense. We've been doing such lousy testing, and still incredibly are using the cannibalistic feeding processes that it's certainly no surprise to find this case -- the surprise is that we actually picked one up."
Prion researcher Aiken agrees that more testing would improve our knowledge. "Testing needs to be ramped up to include the 200,000 downers immediately or as soon as we can. The diagnostic capacity is there, we can do this." More than a dozen diagnostic tests for prion diseases are on the market.
On Jan. 1, the World Health Organization called for pre-slaughter testing of all cows aged 30 months or more.
Expert: exports important
Certainly, nobody has more to lose than cattle raisers, who were starting to enjoy high prices when Washington State loosed it's beefy bummer. If American consumers sustain their confidence in beef, the issue will largely rest on exports, and that picture is grim. "The quickest, hardest, and obvious loss is exports," says McCarty. "We export 9 to 10 percent of our product every year." More than 30 countries, including Japan, the largest market, have banned imports of U.S. beef, wrote CBS news.
On Jan. 11, the USDA cut its estimate of 2004 beef exports by 90 percent.
To McCarty, even the discovery of BSE does not represent a total failure of USDA's efforts. "Yes, keeping it out was the first goal," he says. But the government and industry both agreed on further measures. "We can't assume that it won't get in, so we need surveillance. If it gets in, we need another firewall, the feed ban, because we know that's how it spreads. Then, taking the next step, we need to do everything we can do to ensure that there is no human exposure."
One thing seems clear. Despite the hysteria about beef, despite the British experience, and despite the shifty nature of the infectious prion, it's unlikely that thousands of mad cows are lurking in American herds. The United States, in other words, is not likely to replay the disastrous British experience, says Schaefer. "I'm guardedly optimistic," he says. "I would not say there will not be another case found; that's a precarious position to take, since we do have 100 million cattle in this country. That's the guarded part of my attitude. On the other hand, the risk to our cattle industry is very low, and the risk to people is negligible" because infectious portions are excluded from human consumption.
Variant CJD, the disease humans caught by eating BSE-infected beef, appeared in Britain in 1995. Both forms of CJD are extremely rare, but how many Britons are infected without showing symptoms? Graph: U.S. Food and Drug Administration
Already, says Schaefer, the value of the 1997 feed ban appears in the fact that the two North American cases were born before the ban. "If we found a BSE case that emerged in an animal born after the feed ban was implemented, that would bring into question the adequacy of our preventive measures."
What's a prion?
When scientists talk prions, they’re referring to different varieties of one protein -- PrP -- which appears widely in all mammals. In its normal form (PrPc, the c standing for cellular), the protein sits on the outside of cell membranes and is entirely benign. Presumably, it has a function, but oddly, despite a lot of work on the subject, scientists have yet to pin it down.
What's a prion disease?
PrP can misfold into a shape called PrPSc (named for the disease scrapie), usually through contact with the infectious agent,that bundles into clumps. The clumps cause plaques in the brain that are the trademark of the transmissible spongiform encephalopathies, or TSEs. As the name suggests, an infected brain becomes riddled with holes, until it resembles a sponge, at least under a microscope.
Tiny holes in the brain's grey matter gives the brain of BSE-affected cows a spongelike appearance when tissue sections are examined in the lab. Photo by Dr. Al Jenny USDA.
In people, the most common prion disease is Creutzfeldt-Jakob disease, or CJD, which affects about one person in 1 million. Much rarer are Gerstmann-Straussler-Scheinker syndrome, fatal familial insomnia, kuru and Alpers Syndrome. All human varieties are similar, and with the exception of kuru (which is only known to have occurred among isolated tribes in Papua New Guinea, who once practiced cannibalism) are distinguishable mostly by age of onset.
Cows get bovine spongiform encephalopathy (BSE), AKA mad cow disease. Sheep can contract scrapie, the oldest TSE, and deer and elk can carry chronic wasting disease. Sometimes, as probably happened with mad cow disease in Europe, the disease may jump to another species unlucky enough to eat a diseased animal.
How do people contract prion diseases?
Acquired infection occurs through diet (eating infectious parts of mad cow) or medical procedures (including brain surgery with contaminated equipment), growth hormone injections (which were once extracted from human pituitary glands, which is located near the brain) or corneal transplants. As doctors have identified these routes, medical procedures have changed to eliminate them.
Hereditary transmission, caused a rare mutation in the gene that codes for the normal form of the protein, explains about 15 percent of human prion disease cases.
Spontaneous disease. The prion changes shape for no known reason.
According to the Centers for Disease Control, 213 Americans died of Creutzfeldt-Jakob disease in 2000, including inherited and spontaneous disease. None of the cases was blamed on eating meat.
Whatever their original source, prion diseases seem to undergo a chain reaction in the brain: The distorted form of the prion (PrPSc) causes native PrP to contort into the diseased form. Since prions appear largely in central nervous system tissue -- brain and spinal cord -- prion diseases can spread through eating infected tissue. Most scientists think bovine spongiform encephalopathy (BSE, or mad cow disease) causes the human disease variant Creutzfeldt-Jakob disease (vCJD).
Is there any treatment?
No treatment can cure or control any prion diseases. Although some drugs can relieve pain and muscle spasms, about 90 percent of patients die within a year.
What's the risk?
According to the Centers for Disease Control, the risk of contracting vCJD from BSE-infected beef remains very low in the United States.
Experts say boneless cuts of beef are the safest, since they are least likely to contain nerve tissue. Processed beef products, including hamburger, hot dogs, and sausage, may pose a higher threat since spinal tissue is more likely to enter the product. Mechanically recovered meat, which is extracted from bones at high pressure, is even more risky. Added to ground meat and other meat products as a kind of meat pulp, mechanically recovered meat is facing tighter regulation.
Organic beef, reports Consumers Union, carries the least risk, because organic beef producers do not use animal by-products.
We know they aren't alive, but can you "kill" them?
As lone proteins with no genetic material, prions aren't considered organisms, so they can't be killed. But proteins can be destroyed or, in scientific jargon, "denatured," using enzymes, heat or other means. Prions, however, are notoriously hardy, and resist normal disinfection techniques like boiling or irradiation.
How to stamp out prions? The list is short, the methods vicious:
1. Incineration at 1000 degrees C
2. Autoclaving (steam heating) at 134 degrees C for 15 minutes or longer
3. Exposure to highly concentrated sodium hydroxide (lye) for 15 minutes in a boiling solution.
4. Exposure to concentrated bleach for one hour.
By Judd Aiken (Professor of Animal Health and Biomedical Sciences University of Wisconsin-Madison), Michael Greger (Chief BSE Investigator, Farm Sanctuary, Mad Cow Coordinator, Organic Consumers Association), Rick McCarty (Spokesman National Cattlemen's Beef Association & Daniel Schaefer (Professor of Animal Science University of Wisconsin-Madison). Available in http://whyfiles.org/193prion/. Adapted to be postedd by Leopoldo Costa.
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