Experts Disagree Over Mad Cow Risk

A Harvard School of Public Health (SPH) expert still asserts that mad cow disease presents little risk for the American public, despite claims by a panel of international veterinary experts that the country is highly susceptible to an outbreak.

Following the first American case of the disease two months ago, an International Review Subcommittee (IRS) appointed by the U.S. secretary of agriculture issued a report expressing concerns that current regulations in place do not fully protect U.S. beef consumers. Swiss researcher Dr. Ulrich Kihm, who co-chaired IRS, has said that there could be up to one case of mad cow disease per month in the U.S.

The report’s conclusions, however, sharply contrast with a different report led by SPH lecturer on risk analysis George Gray. The report was commissioned by the U.S. Department of Agriculture (USDA) in 1998 when the first outbreaks in Europe sparked concern in the U.S.

Gray says he disagrees with Ulrich’s finding that the nation could expect up to one case of the disease, more formally known as bovine spongiform encephalopathy, per month.

“Well, we’re already late then, aren’t we? I have no idea where that [number] came from,” Gray said.

IRS co-chair Will Hueston, a professor at University of Minnesota, said Ulrich’s number was just “a phrase taken out of context.”

“We can’t predict how many cases right at this time. And I don’t anticipate a great number of additional cases,” Hueston said.

Hueston said he also believes it is a moot point to predict the number of future cases, as long as the government enacts the IRS recommendation to remove specified risk materials from the animal feed.

The current feed ban in place since 1997 prohibits feeding meat and bone meal with potentially contaminated protein to cows, sheep, goat or deer.

A recent USDA regulation also bans brain and spinal cord materials from cows over 30 months old from entering the human food chain. It is still allowed in animal feed, however.

Gray said this ban provides further reason for Americans to remain calm.

“Mad cow disease cannot become established in the United States, and it does not happen because of the feed ban enacted in 1997,” Gray said.

Gray’s report was based on a computer simulation of current cattle and agricultural practices in the United States. The simulation tested the effects of an introduction of up to 500 infected cattle and concluded that the disease would be eradicated within 20 years, despite the large number of infected cattle used in the study.

Gray said he remained confident that his results were valid because his model accounted for possible lack of compliance with current regulations.

Having spoken last week to members of IRS, Gray said his views are not entirely different, but characterized the IRS report as “pessimistic.”

“We came out all in agreement and nothing was inconsistent. Only some recommendations of what could be done as opposed to what should be done,” Gray said.

Hueston, basing his argument on the difficult European experience in stopping the recycling of animal feed, said he still supports IRS recommendations to ban risky materials, such as brain and spinal cord tissue, from animal feed and pet food.

“[The U.S.] should go ahead and bite the bullet and take these strategic actions now and prevent further spread of the disease,” Hueston said.

He also refuted Gray’s claims that the IRS report was unjustifiably pessimistic.

Hueston said the IRS report is based on “experimental results from around the world, scientific knowledge that has not yet been published, and social science evidence added with personal experience.”

Food and Drug Administration (FDA) spokesperson Linda Grassie wrote in an e-mail that the FDA is currently reviewing the IRS report. Grassie said that the differing conclusions between the Harvard Risk Assessment and the IRS report are “striking.”

“As regulators, we need to understand how the two groups could reach such fundamentally different conclusions,” Grassie wrote.

“We hope that the report writers will make available the scientific evidence supporting some of their recommendations so that we can better understand the reduction in risk to the health of the public that their proposals will achieve,” she wrote.

—Staff writer Carol P. Choy can be reached at choy@fas.harvard.edu.