“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.