Avoiding Mad Cow Disease

by Food and Drug Administration (FDA)

Millions of British television viewers watched the harrowing final days of 14-year-old Zoe Jeffries in October 2000. The ordeal of the young girl from Manchester, England, began more than two years earlier. First she cried for two weeks, then came the hallucinations and continuous screaming. As the disease progressed, the pain in her legs worsened until she couldn't walk. Bedridden, her brain wasting away, she was reduced to communicating through moans and grunts.

Zoe's mother, Helen Jeffries, let the television cameras into her home to demonstrate the plight of people like her daughter — victims of new variant Creutzfeldt-Jakob disease, or nvCJD. The neurological illness is thought to be the human form of bovine spongiform encephalopathy, or BSE-commonly called "Mad Cow Disease." The disease is thus far untreatable, incurable, and ultimately fatal.

"It's a bad disease," says Lawrence Schonberger, MD, MPH, an epidemiologist at the Centers for Disease Control and Prevention (CDC). "We believe that it is transmitted by food that has been contaminated with the agent that causes BSE. Every case of nvCJD is a major tragedy." Although the incubation period after initial exposure can be quite long, once clinical signs and symptoms begin, death usually occurs within about a year.

The recent increase in reported cases of BSE in European cows and the increasing number of human nvCJD cases in the United Kingdom have raised fears throughout the European Union (EU) of the risk of eating beef possibly contaminated with the BSE agent. Although these concerns may have spread to the United States, the diseases have not. No cases of nvCJD in humans or BSE in cows have ever been identified in this country.

BSE and nvCJD have thus far been kept out of the United States largely through the combined efforts of the Food and Drug Administration, the U.S. Department of Agriculture (USDA), the CDC, other federal organizations, and state regulatory and health agencies. These organizations have taken aggressive actions to reduce the risk that BSE could be introduced and spread in this country.

BSE has infected more than 180,000 cattle in the UK and about 1,800 cattle elsewhere in the EU, according to the European Commission's Health and Consumer Protection Directorate, an agency of the EU. Because of UK actions to eradicate BSE since it was first identified in 1986, the number of BSE cases is falling sharply in that country, but it is rising in a number of other European countries.

The sudden rise in reported BSE cases may, in part, reflect increased testing to detect infected cattle by some EU member countries, particularly France, according to Burt Pritchett, a veterinarian in FDA's Center for Veterinary Medicine. "And because of the long incubation period of BSE (two to eight years), cows being identified with BSE now would have become infected several years ago," says Pritchett. "In December 2000, the EU imposed BSE testing EU-wide, which will likely further increase the number of cases being reported."

How BSE Spreads Within Cattle Herds

Evidence suggests that certain contaminated cattle feed ingredients are the source of BSE infection in cattle. The process that leads to the contaminated feed starts when livestock already harboring the BSE agent are slaughtered. After cows and sheep are killed, the edible parts are removed. The inedible remnants are taken to a special plant, where they undergo a process called "rendering." This process creates two major products: fat, which is used in an amazing array of products (such as soap, lipstick, linoleum, and glue), and meat-and-bone meal (MBM), a powdery, high-protein supplement that is often processed into animal feed.

Although the animal remnants are "cooked" at high temperatures during the rendering process, the BSE agent, if present, is able to survive.

When this contaminated MBM is fed to cattle as a protein supplement, the BSE agent can be passed on to many new cattle. It is believed that this is how BSE was spread through the UK cattle herds.

In 1997, scientists at the Institute for Animal Health in Edinburgh, Scotland, and the Imperial College School of Medicine in London presented studies that strongly pointed to the agent that causes BSE as the most likely cause of human nvCJD. The UK government concluded that victims of nvCJD most likely acquired the disease by consuming food that had been made from cattle infected with BSE.

Although BSE and nvCJD occur in different species, they both belong to a family of fatal neurological diseases known as transmissible spongiform encephalopathies (TSEs), so named because of the sponge-like holes they leave in the brain. Currently, no test can reliably detect BSE in live cattle or nvCJD in live humans. A diagnosis is confirmed by examining brain tissue after death. The agent that causes TSEs is not well understood. The prevailing theory of the scientific community is that the agent is a "prion," an abnormal, slowly replicating protein.

"So little is known about prion diseases," says James Voss, DVM, of the College of Veterinary Medicine and Biomedical Sciences at Colorado State University. "It's a very difficult area to study because of the long incubation period of these diseases," says Voss, who is also the co-chairman of the TSE Task Force of the Council for Agricultural Science and Technology, a nonprofit research consortium. "We believe the risk is very, very low that BSE could gain entry to this country, but no one can say with 100 percent certainty that it won't happen."

"We know that our cattle are not immune to this disease just because they live on this side of the Atlantic Ocean," says Murray Lumpkin, senior medical advisor in FDA's Office of the Commissioner. "Renderers, cattle ranchers, feed manufacturers, feed lot operators, and state and federal government agencies will all have to continue to work together vigilantly to assure safe cattle-feeding practices are scrupulously followed. This is our first line of defense against the disease getting into American cattle herds."

Other TSEs are known to occur in sheep, mink, deer, elk, and cats. The recent European outbreak of BSE may have originally resulted from feeding cattle with MBM-supplemented feed made from sheep carcasses infected with scrapie — a TSE found in sheep and goats.

Unlike BSE, other animal TSEs do not appear to be naturally transmitted to humans, according to an October 2000 report of the TSE Task Force. However, five TSEs do occur in humans — all of them rare. In 1957, scientists first recorded a human TSE, called kuru, in the Fore natives of the New Guinea highlands. The Fores were cannibals — they ate parts of their fellow humans, especially brain tissue. It is believed this practice contributed to further spread of kuru in the population.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.