Mad cow disease (search) was diagnosed in a Canadian cow this week, setting off a new round of predictable, but groundless panic.
The U.S. government promptly banned imports of Canadian beef and cattle. Investors dumped the stock of beef-related companies, notably McDonald’s (search), which lost $1.5 billion in market value.
And of course, what health scare would be complete without media hype?
Front-page coverage in the New York Times, for example, reported that eating meat from diseased cattle has allegedly caused more than 100 human deaths in Europe since 1994 and “raised questions about the health benefits of eating beef for many consumers around the world.”
There’s no question that bovine spongiform encephalopathy (BSE), commonly called “mad cow,” is a highly infectious, neurological disease in cattle. But the notion that people can contract a human form of “mad cow” disease by eating beef from infected cows is more bun than burger.
The first epidemic of mad cow broke out among cattle in the U.K. in 1986. Beginning in 1994, human cases of a supposedly novel brain disease, called new variant Creutzfeldt-Jakob disease (nvCJD) began appearing in the U.K.
Though laboratory testing seemed to indicate that BSE and nvCJD were similar, no one could determine with certainty whether and how BSE was related to nvCJD.
There were no geographic areas in the U.K. with significantly higher incidence of people with nvCJD and there were no cases of nvCJD among “high risk” groups such as farmers, slaughterhouse workers or butchers.
When researchers considered the possibility that nvCJD was caused by consumption of beef from BSE-infected cattle, no correlations could be established between nvCJD and any specific meat or dairy product because consumption was so widespread.
Moreover, no one could establish whether any of the nvCJD cases ever consumed beef from diseased cattle.
Researchers nevertheless became fixated on the idea that consumption of infected beef was the culprit behind nvCJD after it was discovered that 1980s slaughterhouse practices and meat preparation inadvertently might have allowed diseased tissue to be mixed up into a variety of packaged meat products such as hot dogs, sausages, beef patties, luncheon meats.
Mad cow mania was on.
But the infected beef theory doesn’t explain why nvCJD tended to occur in young people ─ most cases have occurred among 15- to 25-year-olds. It doesn’t offer the slightest clue as to why only about 130 nvCJD cases have occurred in a British population of 60 million exposed to potentially contaminated beef products.
Some have suggested that a kind of “epidemiological Russian roulette” is at work, where consumption of infected beef results in rare and randomly distributed cases of nvCJD.
The Russian roulette explanation is not a scientific one, however, and not one on which public alarm or public policy should be based.
Despite its gaping holes, the infected beef theory has mutated into orthodoxy among many in the medical and public health community that few have been brave enough to challenge.
One U.K. public health expert, George A. Venters, did manage to have an article published in the British Medical Journal in October 2001 titled, “New variant Creutzfeld-Jakob disease: the epidemic that never was.”
Venters maintains that infected beef theory is wrong and that nvCJD might not even be a new disease.
Venters challenged the biological plausibility of BSE causing nvCJD since there is no direct evidence that the vehicle of BSE infection ─ a special protein called a prion (search) ─ is infectious to humans. Nor is there direct evidence that BSE prions survive cooking, digestion and the human immune system.
Venters points out that the clinical features and pathology of nvCJD are similar to kuru, a prion disease found in Papua New Guinea and spread by cannibalism. The differences in pathology between kuru and nvCJD, says Venters, may be more of degree than kind since nvCJD patients tend to live longer because they get better medical care.
If nvCJD is not a novel disease, then it can’t be tied back to BSE-infected meat from the 1986 mad cow epidemic.
After discussing the numerous deficiencies in the BSE-nvCJD hypothesis, Venters observed, “The evidence that has been amassed is directed towards confirming the [BSE-nvCJD] hypothesis rather than testing it. Salient contrary information has either been played down or ignored.”
BSE-infected cattle should be isolated and destroyed to ensure there is no further spread of mad cow disease among the animals. There is no dispute about that.
But nvCJD is a rare and apparently random disease of uncertain origin. That much knowledge doesn’t justify even the slightest concern about the safety of Canadian beef.
Steven Milloy is the publisher of JunkScience.com, an adjunct scholar at the Cato Institute and the author of Junk Science Judo: Self-defense Against Health Scares and Scams (Cato Institute, 2001).