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Mad Cow Disease On U.S. Soil

Edited by: Mary Schroeder, M.S., R.D. & Pat Kendall, Ph.D., R.D., Colorado State - Winter 2004

Many say it was only a matter of time until cattle infected with the dreaded disease Bovine Spongiform Encephalopathy (BSE), more commonly known as Mad Cow Disease, made its way onto U.S. soil. Thanks to tightened USDA regulations that have been put into place to safeguard our food supply, only one infected cow has been identified to date. No illnesses have been reported of prion-related diseases associated with the infected animal. Recall efforts have been successful, with the majority of the meat from the identified animal being contained within a few days.

Concern remains high due to the many unknowns about this disease and fear that what happened in the United Kingdom could happen here. On a positive note, an independent analysis by Harvard University in 2001 and again in 2003 has shown that the risk of BSE spreading in the United States is low and any possible spread would have been reversed by controls already put in place by the USDA.

BSE belongs to a class of rare brain diseases, called Transmissible Spongiform Encephalopathy's (TSEs). All are associated with the accumulation of abnormal prion proteins (PrP) in the brain. Examples of other TSEs that affect animals include Chronic Wasting Disease in deer and elk and Scrapie in sheep and goats. A number of different TSEs also affect humans, including Creutzfeld-Jakob Disease (CJD), Fatal Familial Insomnia, Gerstmann-Straussler-Scheinker Disease, Kuru, and New Variant CJD (nvCJD or vCJD). Of these, only nvCJD has been associated with BSE or mad cow disease.

New variant CJD differs from classical CJD in several ways. Classic CJD, first identified in the 1920s, is a very rare disease that strikes 1 in a million people worldwide, most of whom are over age 55. Early stages tend to be neurological, such as trouble standing or walking properly, involuntary jerking and speech abnormalities. While the cause of CJD is unknown 85% of the time, it has not been linked to mad cow disease. In contrast, the new variant form (nvCJD) was first documented in Great Britain in 1996 and has occurred almost exclusively in people under the age of 55, a number of whom were teenagers. Transmission is believed to be from consumption of products contaminated with nervous system tissue from BSE-infected cattle. Early nvCJD symptoms are mostly psychiatric (depression, anxiety) in nature. Patients often complain of pain, numbness or a pins-and-needles sensation. Eventually patients become unable to move or speak. Both diseases are fatal. At this point there is no known treatment for either disease.

Since it was first described in 1996, 153 cases of nvCJD have been identified among persons in the United Kingdom and surrounding countries, most thought due to the consumption of products contaminated with central nervous tissue of BSE-infected cattle. Questions remain as to how infected tissue made its way into the food supply in those countries and what the incubation period was before signs of the disease surfaced. However, many changes have been implemented in recent years to prevent the illness from spreading further. For example, the United States has been testing for BSE since 1990 and since 1997, has prohibited the use of any ruminant-derived protein in animal feed.

In response to the U.S. incident of Mad Cow Disease, the USDA has further strengthened protections against BSE. Actions being taken include:

• Disallowing "downed" or sick cattle from entering the food chain;
• Prohibiting air injection stunning of cattle;
• Implementation of a "test and hold" procedure for all animals tested for BSE;
• Prohibiting the use of high risk cow parts (skull, brain, eyes, and spinal tissues of cows over 30 months; small intestines of all aged cows) in the human food supply;
• Prohibiting use of mechanically separated meat in human food.
• Tightened controls on automated carcass stripping systems to better insure that spinal cord tissue isn't nicked;
• Expediting the implementation of a national animal identification program to speed the response rate to disease outbreaks when they do occur.

Sources:

1. USDA News Release Dec. 30, 2003.
2. Beef Cattleman's Association Fact Sheet: New Variant CJD.
3. Crutzfeldt-Jakob Disease Foundation
4. Extension Disaster Educational Network (EDEN)



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