Commentary: Mad Cow: The U.S. Is Not Immuneby
It's a biocontainment nightmare, an Eden gone toxic. Up in the wilds of Saskatchewan, land poisoned with infectious prions--malformed proteins like the ones that cause mad cow disease--have turned hundreds of acres into a death trap for deer and elk.
Although only 14 elk have been diagnosed with chronic wasting disease (CWD) in the past year, ranchers and wildlife biologists fear the worst: an epidemic of a contagious, invariably fatal disease for which there is no live animal test and no cure. No one even knows for sure how it spreads or if it can infect livestock outside the lab. But with a budding elk-ranching industry and thousands of wild animals at risk, the Canadian Food Inspection Agency (CFIA) snapped into action. Since November, 1,500 elk that may have had contact with the sick animals have been slaughtered and their brains saved for testing.
The fate of a few thousand Canadian elk won't keep many Americans awake at night. But it was an animal imported from the U.S. that sparked the outbreak. Worse, CWD is now entrenched in herds running wild in Colorado and Wyoming. Meanwhile, scrapie, a sheep form of the disease, has been found all over the U.S.
TIME BOMBS. A European-style mad cow nightmare seems remote--anywhere outside Europe. But the U.S. is neither isolated nor immune from the prion plague. And though there has never been a diagnosed case of bovine spongiform encephalopathy (BSE) in the U.S., efforts to keep the disease and a related human illness, new variant Creutzfeldt-Jakob disease (nvCJD), at bay may not be enough. Consider the following:
-- According to the World Health Organization, tainted protein feed made from carcasses of sick animals spread BSE in Europe. The feed was sold all over the world, even after Britain imposed a domestic ban on it in 1988. Also, potentially contaminated European meat products were imported to the U.S. well into the '90s.
-- The Food & Drug Administration hasn't effectively enforced its '97 ban against giving feed made from rendered cows to cattle.
-- Screening of blood donors at risk for nvCJD only covers people who lived in Britain during that country's peak mad cow years. But now the problem has spread to Europe. Also, there is no U.S. screening of organ donors, although infectious prions can lurk in various tissues.
-- "Downer" cattle--cows that fall down and can't get back up--are considered a high-risk group for BSE. But they can be slaughtered at FDA-supervised rendering facilities, avoiding inspection and testing by the U.S. Agriculture Dept.
Among all deadly pathogens, prions present a particularly hairy set of challenges to health authorities. Normal forms of prion proteins exist in almost every mammalian cell. But when healthy prions come in contact with their deformed cousins, they refold into poisonous proteins that eventually corrode the brain.
Prions are a hardy lot, able to withstand radiation, temperatures of 600F, and standard hospital disinfection. In Europe, policies that underestimated the threat have proven disastrous. "It reminds me of the early days of HIV, when the blood industry wouldn't do anything," says Michael Hansen, who analyzes U.S. prion disease policies for the Consumers Union. "If you want to forestall disaster, you have to take a precautionary approach," he says.
That's not always easy. The extent of environmental contamination from CWD in Colorado and Wyoming spans 15,000 square miles. Any effort to destroy the 80,000 deer and elk in the region--only a small percentage of which have the disease--would be pointless, says University of Wyoming veterinarian Elizabeth S. Williams. While bad feed is blamed for spreading BSE, scientists believe prions from CWD and the sheep disease scrapie can be shed through mucus and feces, thus infecting the land.
TOSSING THE DART. Williams--who hunts and eats venison--doesn't see CWD as a direct danger to people. But others do. Hansen notes that human prions in a test tube are just as susceptible to CWD as to BSE. This means CWD could be just as bad as mad cow, especially if CWD "jumps species" and gets into commercial livestock. While early tests indicate that's unlikely, it will be years before anyone is sure.
Dangerous agricultural practices in the U.K. produced a tragedy. First, carcasses of sick cows jam-packed with infectious prions were recycled as feed. Only 180,000 cows were ever diagnosed with BSE, but scientists believe nearly one million were actually infected. And although there have been fewer than 100 cases of nvCJD, the total could rise to more than 100,000, according to several European authorities on the disease.
In 1997, the FDA tried to put up a fire wall by making it illegal to give supplements of cooked ruminant remains--including elk--to cattle and sheep. But that action may have come too late. In the wake of a similar ban in 1988, British companies sold off stocks of poisoned feed. "We didn't find a region of the world that didn't get these materials," says WHO medical officer Dr. Maura N. Ricketts. Mislabeled feed contributed to the spread of BSE in Europe, she says.
In the U.S., inspections have been a problem. In the two-plus years since the FDA ban has been in place, only two-thirds of licensed feed mills have been inspected; in 20%, the feed was not labeled properly. Only half the estimated 8,000 unlicensed mills have been inspected--of which 40% were found in violation of labeling requirements. Now, with thousands of tons of tainted feed stockpiled in Europe, there's concern that smuggled product could get into the mix.
Livestock testing also seems to be inadequate. Months prior to showing symptoms, cows can have infectious BSE--and there's no sure way to find out. Last year, the USDA examined just 2,600 cows--all of them either "downers" or neurologically damaged animals that are considered to present the highest risk. Linda A. Detwiler, USDA's BSE surveillance coordinator, would like to expand testing. But with 100 million cows and no reported BSE cases in the U.S., "where do you throw the dart?" she asks.
Food isn't the only way to spread poisonous prions. Blood, long considered safe, has recently come under scrutiny. "The infectivity levels are low and not very efficient. But it's there, no question about it," says Robert Rohwer, director of neurovirology at the Veterans Administration Medical Center in Baltimore, and a consultant to the Red Cross, FDA, and European Union on blood issues. Tissues for surgical transplants--everything from corneas to knee tendons--represent another transmission risk. Yet in the U.S., there is no screening for nvCJD.
Billions of dollars have now been spent on eradication since mad cow was first diagnosed in 1985. But it is the growing number of nvCJD victims who are the reminders of the true price to be paid for today's shortsighted policies. A recent move by the USDA to tighten the import ban on meat and meat by-products from Europe is a step in the right direction. So is the FDA's review of blood and tissue donor policies. But as long as there are wild cards such as CWD--and tons of BSE-tainted feed sitting in storage--the danger cannot be minimized.