Mad Cow Disease Hits Home

Image Gallery Cattle continue to be at risk or contracting mad cow disease from feed because high-protein bovine blood is used in the ""milk replacer"" routinely fed to dairy calves, and sometimes to beef-breed calves, too. Ken Hammond/USDA

Fifteen years after Great Britain began destroying 3.7 million cattle because of an epidemic of mad cow disease, the first U.S. case of mad cow was confirmed in December in Washington state. The infected cow already had been slaughtered, and its meat dispersed into the human food supply.

Initially, the USDA reported the cow was a "downer"—an animal too sick to walk, which is a possible sign of mad cow infection—but subsequent eyewitness reports have disputed that claim. Determining the animal's status is important because downers are targeted in the USDA's mad cow surveillance plan.

Mad cow (also called BSE or bovine spongiform encephalopathy) is a fatal cattle disease that causes spongelike holes in the brain, making the infected animal stagger—thus the descriptive term "mad" cow. Scientists think animals develop the disease by eating feed containing brains, spinal cords or central nervous system tissues of other infected animals. (Yes, our industrial food system has been feeding cattle parts back to cattle! For more on this topic, see "Cattle Futures," Page 24.)

The human form of this disease is called variant Creutzfeldt Jakob Disease (vCJD), and relatively few people are thought to have been infected by eating nervous-system tissue from diseased cattle. Mad cow and vCJD are caused by prions, infectious protein particles that cannot be destroyed by cooking. According to the USDA, the risk of humans contracting the disease by eating U.S. beef is extremely low, but consumer groups say the agency is not doing enough to protect the public. The Centers for Disease Control and Prevention so far confirm 153 cases of vCJD worldwide, with 143 of those in the United Kingdom.

Since the outbreak of mad cow disease in the 1980s in Europe, consumer groups have urged the USDA to adopt stringent testing and tracking rules for beef. But, the beef industry resisted. A week after the U.S. mad cow case was confirmed, the USDA finally announced it would implement a national identification system to track meat, and ban downer cattle and mechanically separated meat from the human food supply. Beef producers also must follow new, more-stringent guidelines when using Advanced Meat Recovery (AMR) systems. AMR systems strip meat dose to the spinal cord and increase the odds that BSE-infected central-nervous tissue could enter the human food supply.

Three-quarters of processing plants that use AMR systems produce meat containing spinal-cord tissue, a 2002 USDA study estimates. Ground-beef products such as hot dogs and hamburger (including pizza toppings and taco fillings) are most likely to contain stripped meat. Marrow in the bones of muscle cuts could contain spinal cord tissue, too. Milk and milk products are not thought to be at risk of contamination.