University of Louisville neurologist Robert P. Friedland, M.D., questions the safety of eating farmed fish in Journal of Alzheimer’s Disease, adding a new worry to concerns about the nation’s food supply.

Friedland and his co-authors suggest farmed fish could transmit Creutzfeldt Jakob disease--commonly known as mad cow disease--if they are fed byproducts rendered from cows. The scientists urge government regulators to ban feeding cow meat or bone meal to fish until the safety of this common practice can be confirmed.

“We have not proven that it’s possible for fish to transmit the disease to humans. Still, we believe that out of reasonable caution for public health, the practice of feeding rendered cows to fish should be prohibited,” Friedland said. “Fish do very well in the seas without eating cows,” he added.

Creutzfeldt Jakob disease is an untreatable, universally-fatal disease that can be contracted by eating parts of an animal infected with bovine spongiform encephalopathy (BSE or mad cow disease). An outbreak in England attributed to infected beef prompted most countries to outlaw feeding rendered cow material to other cattle because the disease is so easily spread within the same species.

The risk of transmission of BSE to humans who eat farmed fish would appear to be low because of perceived barriers between species. But, according to the authors, it is possible for a disease to be spread by eating a carrier that is not infected itself. It’s also possible that eating diseased cow parts could cause fish to experience a pathological change that allows the infection to be passed between the two species.

“The fact that no cases of Creutzfeldt Jakob disease have been linked to eating farmed fish does not assure that feeding rendered cow parts to fish is safe. The incubation period of these diseases may last for decades, which makes the association between feeding practices and infection difficult. Enhanced safeguards need to be put in place to protect the public,” Friedland said.

There have been 163 deaths from Creutzfeldt Jakob disease in the United Kingdom attributed to eating infected beef. Bovine spongiform encephalopathy has been identified in nine Canadian and three U.S. cattle.