1. Mad cow comes to town!

2. Mad-cow history

3. "Abundant caution" or half-measures?

4. Making sense of the threat

5. The weirdest agent

GLOSSARY:
Bovine spongiform encephalopathy (BSE): Mad cow disease.

Chronic wasting disease: A TSE in deer and elk.

Creutzfeldt-Jakob disease (CJD): Fatal, human TSE, strikes one person in a million.

Prion: A protein that, when misshapen, can cause other prions to fold wrongly. Causes all TSEs.

Scrapie: A TSE in sheep. Known since the 1700s; does not infect people.

Transmissible spongiform encephalopathy: TSE. Infectious brain diseases caused by prions.

Variant CJD (vCJD): The "human" version of mad cow. Similar to CJD; strikes younger people.

Although they are all caused by an accumulation of misfolded protein, the various human TSEs affect different areas of the brain. GSS = Gerstmann Straussler Scheinker syndrome; FFI = fatal familial insomnia; two extremely rare inherited brain diseases. Image: © McCusker and Novakofski, University of Illinois

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."

Will the new USDA regulations keep meat safe?

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.

USDA

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.

The issue in cows depends on how infectious dried blood meal actually is, says Rick McCarty, a spokesman for the National Cattlemen's Beef Association. " Dried blood meal is an allowable nutrient supplement, even in cattle feed, according to the FDA [Food and Drug Administration], simply because there's been a lot of research looking for infectivity in bovine blood, and it's simply not been found."

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."

What are these cows eating? Britain now prohibits farmers from feeding cattle by-products to other animals. But critics say U.S. regulations have loopholes. Photo: USDA

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" (see "Use of a Marker..." in the bibliography). 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.

Downed cow in stockyard.
© Farm Sanctuary

Although the Washington-State mad cow was a downer, she did not show the gait problems found in the typical mad cow. Instead, her problem was postpartum paralysis; if her brain was damaged, rather than just infected, by BSE, it apparently did not cause symptoms. "It seems almost a fluke," says Greger. "Presumably if she'd not had that birthing injury, she would not have been tested and we'd still be able to call ourselves a BSE-free country."

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.

At any rate, USDA plans to double testing to 40,000 cows per year.

So is the sky falling?

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