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It's also tissue from dead animals that's thought to be responsible for the BSE epidemic; to understand why, you have to know a little bit about the people who call themselves "the silent industry." U.S. farmers, ranchers, and vets have some 40 billion tons' worth of carcasses and slaughterhouse waste on their hands each year. Landfilling or burning it all would be a hassle and expensive. So instead, most of the dead meat goes to places like Greg Vanhoven's family business in South St. Paul.
Vanhoven Co. is a rendering--or, as Greg Vanhoven prefers to put it, food waste recycling--plant, one of perhaps a dozen in Minnesota and several hundred nationwide in a business that melds blood and gore with high tech. The trade press describes "spray- dry" machines that turn blood into a fine, brown powder (gardeners know it as blood meal); gigantic kettles that boil fat to make tallow; grinders that crush bones into minuscule fragments. Vanhoven Co., which processes mostly waste from the nearby slaughterhouses, sells by-products to paint and paint thinner manufacturers and cosmetics companies. But his, and most renderers', biggest customer is the feed industry: It buys "animal meal" that is added to the diets of everything from cows to turkeys and pets as a high-powered nutritional supplement.
Vanhoven, an amiable man who likes to explain what he considers a vastly misunderstood business, says it was clear to him almost from the start that BSE was "a bad situation." The British epidemic is now widely thought to have come from cattle eating the processed leftovers of scrapie-infected sheep. Vanhoven says his company has had a policy for several years now of not accepting sheep and other animals that have been found to have TSEs in the U.S.; he says it's just not a risk worth taking.
There is, it's worth noting, no proof that it was sheep parts that started the epidemic in cows--or, for that matter, that humans can get CJD from eating cows. But there is evidence that TSEs can be transmitted orally, and that they can jump from one species to another. In England, mad cow panic first hit in 1989, when domestic cats and zoo felines started dropping dead with their own form of spongiform encephalopathy; their food, too, contained material from rendered sheep and cows. More recently, French researchers have found that monkeys can get a CJD-like version of TSE when they are fed meat from BSE cows. And, perhaps most intriguingly, researchers recently announced that humans and cows have a striking similarity in their genetic sequences right at the spot that's thought to be implicated in prion production.
If BSE can be passed to humans, the scale of the outbreak is anyone's guess. The British scientific advisory commission reviewed 10 cases of the new, "variant" CJD, and 10 more have since been diagnosed in Britain. In the U.S. there are no known cases, though doctors suspect CJD in a 24-year-old upstate New York woman whose family says they ate some British cutlets sent as a gift when she was a teen.
In the long term, one researcher has estimated up to 500,000 people could die from CJD in Britain as a generation exposed to BSE grows up. Others put the figure closer to 5,000. Either way, the cases would only begin showing up now: CJD has about a 10-year incubation period, and it's been about that long since the beginning of the BSE epidemic.
Thus far, the key tenet of the BSE debate in the U.S. has been that the disease does not exist in this country--or, as they note when questioned, only exists at a very low level. USDA officials have acknowledged that American cows like any others would be expected to develop BSE "sporadically" (without being infected), at a rate of about one in a million; in a herd of 100 million, give or take a few, those cases are unlikely to be discovered, especially since there is not an approved test to check for the disease in live animals. USDA's 10-year-old BSE surveillance program consists largely of asking slaughterhouse inspectors to watch for cows with suspicious symptoms and send in their brains for autopsy. Several thousand brains have been thus examined, and none showed the typical spongy pattern.
There is, however, something mysterious killing U.S. cattle. Upton Sinclair first described it in The Jungle--animals that would simply lay down and never get up, no matter how much you pushed or prodded them. Some "downers" are looked at by vets, some aren't; some, but not all, are diagnosed with a known disease. Most go to rendering while a few become hamburger. And some are picked up by dead-animal haulers--a fascinating little subset of the rendering industry consisting, as one expert puts it, "basically of guys with pickup trucks who have their territories, and when they step on each other's toes they meet in back of a bar."
Among the haulers' customers are people who raise carnivores on a large scale, such as mink farms. Mink, as it happens, have their own form of TSE; a couple of times a decade there's an outbreak that wipes out a farm or two. How the mink get the disease is another mystery, one UW-Madison veterinary science professor Richard Marsh has been studying for several decades.