Mad cow disease raises concern but safety nets are in place says USDA

By Dr. Ananya Mandal, MDApr 26 2012

A case of mad cow disease confirmed in California has raised concern regarding food safety. But experts say that is not the only worry.

“What we know is that 3,000 Americans die every year from preventable food-borne illnesses that are not linked” to mad cow disease, said Sarah Klein of the consumer advocacy group Center for Science in the Public Interest. “Things like E. coli, salmonella — that's where we should be focusing our attention, outrage and policy.”

Four sick cows ever discovered in the U.S., the one announced Tuesday being the first since 2006, and no human version of the illness linked to eating U.S. beef, is not enough to worry about. “From simply a public health issue, I put it very, very low,” Cornell University food safety expert Martin Wiedmann said of the level of concern about mad cow disease. Maintaining confidence in exports fuels the nation's monitoring of the beef supply as much as continuing safety concerns, he said.

Routine testing of a dead dairy cow from central California showed the animal had bovine spongiform encephalopathy, or BSE, a disease that gradually eats holes in the animal's brain. U.S. health officials were adamant that there was no risk to the food supply — the cow never was destined for the meat market, and the World Health Organization says humans can't be infected by drinking milk from animals with BSE. In any case, the animal tissues that can carry the BSE — including the brain and spinal cord — are removed from cattle before they're processed for food.

In addition, the U.S. surveillance program tests brain tissue taken from about 40,000 dead cows a year for BSE. That testing is designed to target the animals most at risk, said Dr. Richard Breitmeyer, who heads the University of California, Davis, laboratory that initially discovered the latest case.

The USDA hasn't released details about the California cow, but a spokesman for U.S. Rep. Devin Nunes of California said the sick 5-year-old came from Tulare County, the No. 1 dairy-producing county in the nation.

The last two cases found in the U.S. were atypical as well. Only 10 cases around the world have been found with atypical characteristics, according to Lyndsay Cole of USDA's Animal and Plant Health Inspection Service. “It's very, very rare,” said Wiedmann, adding that some research suggests that this sporadic type would be even less easily transmitted to people through meat than traditional BSE. There's a human form completely unconnected to contaminated meat called classic Creutzfeldt-Jakob disease.

BSE is caused by a build-up of abnormal proteins (called prions) in animals' brains. It takes two to eight years -- five on average -- for an animal to develop BSE symptoms. The rapid test can't detect BSE until an animal is on the verge of symptoms. Most U.S. food cattle however, are slaughtered before they are 2 years old.

BSE can cause infected animals to display nervousness or aggression, difficulty in coordination and standing up, decreased milk production or weight loss. It is usually transmitted between cows through the practice of recycling bovine carcasses for meat and bone meal protein, which is fed to other cattle.

The reason why mad cow disease became a problem is that ground-up cattle were being put in cattle feed. The FDA banned this practice in 1997. The USDA points to this ban as a major factor in the safety of U.S. beef. But chickens can be given feed containing pellets of ground-up beef. It takes years for a person infected with BSE to develop the fatal human disease called variant Creutzfeldt-Jakob disease or vCJD.

“The safety of our food is addressed through our interlocking safeguards and removal of any type of material that contains the BSE agent in the U.S.,” USDA Chief Veterinary Officer John Clifford said yesterday. “Our livestock population is one of the healthiest in the world. Consumers should be confident in our food supply.”

On Wednesday, a major South Korean retailer suspended sales of U.S. beef. But live cattle futures, which had dropped Tuesday, recovered as it became clearer that exports would not take a significant hit.